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Fall migratory flight initiation of the potato leafhopper, Empoasca fabae (Homoptera: Cicadellidae): observations in the lower atmosphere using remote piloted vehicles
Agricultural and Forest Meteorology 97 (1999) 317–330
Fall migratory flight initiation of the potato leafhopper, Empoasca fabae (Homoptera: Cicadellidae): observations in thelower atmosphere using remote piloted vehicles Elson J. Shields ∗ , A.M. Testa Department of Entomology, 4144 Comstock Hall, Cornell University, Ithaca, NY 14853, USA Accepted 21 July 1999
Abstract The development and use of a remote piloted vehicle (RPV) to sample the lower atmosphere for potato leafhopper has shown a correlation between declining barometric pressure associated with the approach of a weather front and the presence of diapausing leafhoppers 30 m above an alfalfa field initiating their fall migration to the southern states. Population decline of leafhoppers in the source field was also correlated with the passage of weather fronts. The RPV utilized in this research had a 2.4 m wingspan and was outfitted with a fine mesh 41 cm2 insect net. This RPV sampled 167 m3 /min with flight durations of 30 min ©1999 Elsevier Science B.V. All rights reserved. Keywords: Potato leafhopper; Empoasca fabae; Remote piloted vehicle; Aircraft; Aerial sampling; Migration
1. Introduction The potato leafhopper, Empoasca fabae (Harris) (Homoptera: Cicadellidae), has been recognized as a serious pest of many crops in the United states since the mid-1800s (Delong, 1938). This insect is highly polyphagous, capable of successful reproduction on over 200 plant species in 25 different families (Poos and Wheeler, 1943, 1949; Lamp et al., 1989). Potato leafhopper is clearly a migratory insect which overwinters in the southern US (Taylor et al., 1992; Taylor and Shields, 1995a), migrates northward each spring utilizing the spring weather systems (Medler, 1957; Huff, 1963; Pienkowski and Medler, 1964; Carlson et al., 1992; Taylor and Shields, 1995b), ∗ Corresponding author.: Tel.: +1-607-255-8428; fax: +1-607-255-0939 E-mail address: [email protected] (E.J. Shields)
and returns in the fall to the overwintering area in reproductive diapause, assisted by the movement of the fall weather systems (Taylor and Reling, 1986; Taylor et al., 1995a). The lack of genetic variation between widely separated populations, both spatially and temporally, supports the hypothesis that potato leafhopper has an annual circular migration (Taylor et al., 1995b). Once initiated, long-distance leafhopper migration appears to be passive in nature (Medler, 1962; Taylor, 1985). This is typical for migratory movement occurring above the first few meters of the atmosphere, and is a consequence of insect airspeed generally being much less than the speed of the wind (Drake and Farrow, 1988). Migrating leafhoppers have been collected at heights as great as 1220 m (Glick, 1939, 1960) and leafhoppers maintaining this altitude may be transported approximately 30% faster than leafhoppers at 300 m above ground level (AGL) (Pienkowski and Medler, 1964), and in a direction which would
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differ according to prevailing environmental conditions (Scott and Achtemeier, 1987). Limits on the altitudes at which leafhoppers will be transported are imposed by the vertical temperature structure of the atmosphere. Wellington (1945a) found leafhoppers in flight folded their wings when the surrounding air temperature dropped below a flight termination temperature threshold. This wing folding causes the insect to drop until air temperatures above the flight initiation threshold are encountered, or flight is terminated at the ground (Taylor and Reling, 1986; Wellington, 1945b). Taylor and Reling (1986) reported that the highest numbers of potato leafhoppers were trapped when the air temperature exceeded 15◦ C and all potato leafhopper trapping ended when the temperature dropped below 12◦ C. A critical factor to understanding potato leafhopper migration is the suite of environmental cues which initiate the flight activity ultimately resulting in migration. Taylor (1985) reports that potato leafhoppers show strongly crepuscular flight behavior, and that substantially more activity occurs during the evening flight period. McDonald and Farrow (1988) observed that the migration initiation of Nysius vinitor Bergroth (Hemiptera: Lygaeidae) corresponded with the disturbed weather associated with prefrontal airflows. This behavior suggests that falling barometric pressure influences migration initiation for this insect. Research focused on identifying the key environmental and physiological factors triggering the initiation of migration requires that individual leafhoppers be collected in the lower atmosphere shortly after the initiation of migration to allow a comparison of emigrating individuals to the population of leafhoppers in the source area or field. Sampling the lower atmosphere for insects and other biota has always been a challenging task for aerobiologists. Scientists frequently use sampling devices located on the ground with tall chimneys, on the roofs of buildings or attached to towers, balloons, and blimps in an attempt to sample in the lower ca. 100 m of the atmosphere for biota. The deployment of stationary traps is often limited by the distribution of suitable objects on which to mount them (i.e., roofs of tall buildings, communication towers) where permission to locate traps may be difficult to obtain, and the sampling efficiency of these traps may be adversely affected by the disruptive air turbulence caused by the
presence of the building or tower. In most cases, the sampling capacity of the device is directly dependent on the surrounding wind speed and the efficiency of the device may be quite variable over the wide range of wind speeds encountered. In addition, many of these devices have limited usefulness when wind speeds exceed 7 m/s, and have low sampling rates. Mobile sampling devices are usually mounted on manned aircraft (light aircraft, helicopters) for the atmosphere above 152 m AGL (FAA lower limit for flight) and provides sampling for the planetary boundary layer (Glick, 1939, 1960; Reling and Taylor, 1984; Isard et al., 1990). These aircraft-mounted devices provide the flexibility of sampling large quantities of air at any altitude above 152 m. Operation of aircraft requires a certified pilot and usually have operating costs in excess of $100/h. Modification to the airframe for attaching of nets or other sampling devices requires FAA approval with the aircraft subsequently designated as an experimental aircraft. An experimental aircraft designation is usually coupled with increased insurance rates and other use limitations. For safety reasons, sampling the lower atmosphere with manned aircraft is limited to time periods with low levels of turbulence and vertical wind shear. Because the transition zone between the surface boundary layer and the planetary boundary layer is generally considered to be 2–2.5 times the crop canopy height in agricultural settings (Huschke, 1989), sampling the atmosphere for biota between 0–152 m is critical to the understanding of long-range transport initiation for organisms. This depth (0–152 m altitude) is the transition zone between insects and other biota in the local dispersal mode and insects and other biota escaping the surface boundary layer into the faster moving air of the planetary boundary layer to disperse long distances. Remote piloted vehicles (RPVs) outfitted with nets or other sampling devices can safely operate within this transition zone (30–150 m) in turbulent conditions with wind speeds between 0–15 m/s (Gottwald and Tedders, 1985, 1986; Tedders and Gottwald, 1986). With air speeds of ca. 20 m/s and greater, RPVs offer air sampling independent of surrounding wind speed and sampling capacities significantly greater than most fixed location sampling devices. Operational costs are also significantly less than manned aircraft. RPVs of moderate size (2.5–4 m wingspans) could be used to
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collect biota within the transition zone if the aerial density of the target organism overlaps the air sampling capacity of the RPVs. The aerial density of the target organism dictates the volume of air that must be sampled per sampling period and the maximum air sampling capacity of the sampling platform (RPV) strongly influences the duration of the sampling period and the time series resolution of the aerial samples. Larger, more powerful and more expensive RPVs can sample larger quantities of air per unit time and result in more of the target organism or a finer time series resolution to characterize fluctuations in the aerial densities of the target organism. While the aerial density of organisms widely fluctuates and is often unknown, our research results using RPVs indicate the aerial density of Fusarium graminearum ascospores range from 0 to 1000 spores per 1000 m3 of air sampled with 30 ascospores per 1000 m3 typical. This range of aerial densities was measured during May–June within an agricultural region in central New York and include data collected over source areas (agricultural fields) and forested areas at least 1 km from the nearest agricultural field. Aerial density of potato late blight, Phytophthora infestans sporangia, ranges from 0 to 1000 sporangia per 1000 m3 of air sampled with 200–400 sporangia per 1000 m3 typical. Aerial collections were made ca. 60 m above a late blight infested potato field. The aerial density of insects over alfalfa fields during late summer in the late afternoon – early evening at 30–50 m altitude range from 0 to 60 individuals per 1000 m3 of air sampled with 5 insects per 1000 m3 typical. In these collections, the aerial density of potato leafhopper, Empoasca fabae, the target organism never exceeded 2 per 1000 m3 with 0.4 leafhoppers per 1000 m3 typical. These densities were similar to densities reported by Taylor and Reling (1986) towing nets from a small plane at ca. 152 m in altitude. Similar RPV collections during the summer months over mixed hardwood forest yielded an average aerial density of 3.7 insects per 1000 m3 . Researchers from the University of Illinois, using collection pods mounted on a full sized manned helicopter, report aerial density of insects within clear air radar echo seldom exceeding 30 insects per 1000 m3 of air sampled with fewer than 5 insects per 1000 m3 typical. Aphids, the target insect, seldom exceeded
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20 individuals per 1000 m3 with 3 individuals per 1000 m3 a more typical occurrence (Isard et al., 1990). These data indicate that the aerial density of fungal spores and insects frequently differ by one order of magnitude. Therefore, aerial density presents a different set of problems for each organism and requires a RPV designed specifically for the task. 1.1. Designing a RPV for aerobiological sampling: An RPV capable of sampling 160 m3 /min (5000 m3 / 30 min) is relatively easy to assemble using ‘off the shelf; components with a total cost of approximately $2500/vehicle (Appendix A). A 50% increase in air sampling capacity (240 m3 /min) more than doubles the cost of the basic RPV, due to a more costly engine and extensive modifications to airframes to tolerate the additional weight and stresses from the additional air sampling capacity. The RPVs with an engine capable of sampling ca. 500 m3 /min require custom built airframes with wing spans increasing to nearly 4 m (from 2.4 m) and take-off weights increase to 25 kg (up from 10 kg) with a cost that can easily exceed $10 000/RPV. These costs are for the basic RPV without instrumentation. Generally speaking, larger RPVs have more flexible payload capacities for items not required for the direct operation of the RPV. For example, a RPV with a 1.75 m (70 in) wingspan has a useful payload capacity of 1–1.5 kg. A RPV with a 2.4 m (96 in) wingspan has a useful payload capacity of 2.5–2.7 kg while a RPV with a 4 m (144 in) wingspan would have a useful payload of 4–5 kg. Wing loading of RPVs in this size range need to remain below 11 kg/m2 of wing area. The amount of fuel required for a given sampling period has a direct impact on the payload capacity that could be used for sampling devices and instrumentation. 2. Research example: use of RPV to collect potato leafhopper initiating fall migration 2.1. Methods and materials In both 1997 and 1998, an alfalfa field was located with a large potato leafhopper (PLH) population. Sweep net collections of potato leafhoppers were made
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Fig. 1. (A) Aerial spore trap constructed from soda bottles. (B) RPV aloft with sample bottles open. (C) RPV with insect net closed for takeoff and landing (D) RPV with insect net open aloft. (E) RPV with a disabling structural problem. (F) Aerial sampling for potato leafhopper as a weather front approaches.
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Fig. 2. Field populations of potato leafhopper in 1997 and 1998. Weekly collections were separated by nymphal lifestage, adults sexed and females were dissected for the presence of eggs.
three times per week starting in mid-August and continuing until late-September. Each sample was sorted by nymphal instar and the adults were separated by sex. All females were dissected for the presence of eggs. In 1998, daily flights with a net-equipped remote piloted vehicle (2.4 m wingspan) (Fig. 1C, D) were used to collect adult leafhoppers flying 20–40 m above the alfalfa field. Sampling flights were 30 min in duration with an average of 5000 m3 sampled during each flight. Flights were initiated on 28 August and terminated on 6 September. The initial flight was taken each day at 5 p.m. and the final flight was taken after dark usually ending around 8 : 30 p.m. All leafhoppers captured aloft were sexed and the females were dissected for the presence of eggs. Prior to each flight, air temperature, relative humidity, cloud cover and wind observations were recorded.
Each year, barometric pressure was continually recorded for the duration of the study, and daily weather maps illustrating the presence of weather fronts were printed and stored for historical comparisons with sweep net and aerial capture data. In both years, individual male leafhoppers were collected from the field population to verify that the field population was E. fabae.
2.2. Results and discussion Field populations of PLH were very high in both 1997 and 1998, with all life stages present in the field at the start of the study (Fig. 2A, C). Newly emerged adults were always present in the field as each nymphal stage matured. In both years, adult field populations
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Table 1 Potato leafhopper aerial sampling log Date (1998)
Collection Relative time humidity
Temperature Barometric Sunset pressure (mm/Hg)
28 August
5 : 45 p.m. 7 : 00 p.m. 8 : 00 p.m. 6 : 00 p.m. 7 : 00 p.m. 8 : 00 p.m. 9 : 00 p.m. 6 : 00 p.m. 7 : 30 p.m. 8 : 30 p.m. 9 : 00 p.m. 5 : 45 p.m. 6 : 44 p.m. 7 : 25 p.m. 7 : 45 p.m. 8 : 31 p.m. 5 : 45 p.m.
55% 70% 75% 85% 85% 100% 100% 60% 80% 85% 85% 50% 50% 60% 60% 70% 80%
29◦ C 27◦ C 23◦ C 25◦ C 23◦ C 19◦ C 18◦ C 24◦ C 21◦ C 17◦ C 17◦ C 24◦ C 23◦ C 18◦ C 18◦ C 16◦ C 21◦ C
760.73 760.73 760.48 758.95 758.95 759.21 759.46 761.75 761.75 762.25 762.76 761.49 761.49 761.49 761.49 761.49 754.38
0 7 : 52 p.m. 0 0 0 7 : 50 p.m. 1 2 1 0 7 : 45 p.m. 1 0 0 0 4 7 : 42 p.m. 3 2 0 0
0 0 0 0 1 3 1 0 1 0 0 0 2 2 2 0 0
7 : 05 p.m. 7 : 22 p.m. 7 : 50 p.m. 5 September 6 : 00 p.m. 7 : 00 p.m. 7 : 30 p.m. 6 September 6 : 00 p.m. 7 : 15 p.m. 11 September 6 : 47 p.m.
85% 90% 90% 55% 55% 70% 60% 60% 70%
18◦ C 17◦ C 15◦ C 24◦ C 23◦ C 20◦ C 29◦ C 28◦ C 24◦ C
754.63 754.63 754.63 763.78 763.78 763.78 757.17 757.17 758.70
0 7 : 39 p.m. 2 0 1 3 7 : 31 p.m. 2 0 7 : 29 p.m. 8 7 : 23 p.m. 5
1 5 0 0 5 1 0 10 5
29 August
31 August
1 September
2 September
showed major declines with the passage of weather fronts (Fig. 2B, D), but the adult population levels rebounded with the maturation of late instar nymphs. In 1997, the majority of leafhoppers had departed from the field by 19 September. In 1998, the field was cut on 11 September and the study was terminated. In both years, data suggest that oviposition had diminished to a very low level prior to the initiation of field sampling. These results are consistent with the presence of late summer reproductive diapause reported by Taylor et al. (1995a). The data also support the idea that newly emerged adults leave the field shortly after eclosion, and the decline of the adult population after the passage of a weather front suggests that the two events are related. In 1998, a total of 76 leafhoppers were captured aloft with the use of RPVs. Forty of the individuals were females and upon dissection, no eggs were
Male versus female PLH caught
Observations
clear skies, winds calm clear, winds calm lightly overcast clear, winds calm clear, winds calm clear, winds calm clear, winds calm clear, winds from the west 10–15 mph clear, winds from the west 10–15 mph clear, winds from the west 10–15 mph clear and calm scattered clouds, winds calm upper layer clouds, calm hazy skies, calm hazy and calm clear skies and calm thunderstorm passed through 1 h earlier now fairly clear, NW winds 5–10 mph upper level clouds, calm mostly clear and calm clear and calm clear and calm mostly clear and calm clear, west wind 5–10 mph clear, west wind 5–10 mph clear, gusts 5–10 mph
present in any individual, suggesting that all the females captured aloft were in reproductive diapause (Table 1, Fig. 3). Most individual leafhoppers were alive after the completion of a 30 min collection flight, but the laboratory verification of reproductive diapause was not attempted due to the relatively low number of collected individuals. All collected males were identified as E. fabae. Whenever possible, the initial evening flight was taken between 2 and 1.5 h before sunset. Leafhoppers were never collected during flights in this time period. On one occasion late in the season (5 September), the initial flight was taken 1.5–1 h before sunset and a single leafhopper was caught (Table 1). The largest numbers of PLH were collected aloft during the time period of sunset ±30 min. The aerial samples indicated that the PLH activity period leading to flight into the planetary boundary layer where long range transport
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Fig. 3. Potato leafhoppers collected aloft with a remote piloted vehicle (RPV) during 30 min collection flights sampling ca. 5000 m3 of air during the sampling period.
occurs, starts approximately 1 h before sunset and ends approximately 30 min after sunset. In our study, 95% of the leafhoppers caught aloft ca. 30 m above the alfalfa field were flying during this time period (Table 1). These aerial collection data support observations reported by Taylor and Reling (1986) that aerial densities of PLH at 152 m are the highest at 20 min after sunset. When barometric pressure changes are compared to the number of PLH captured aloft, data suggests that PLH migratory flight is correlated with declining barometric pressure prior to the normal PLH evening activity period around sunset. On 28 August, the barometric pressure was dropping just prior to the aerial sampling period and no PLH were collected aloft (Fig. 4A, Table 1). The pressure had dropped 4.8 mm Hg in the previous 18 h. However, on 29 August with the pressure dropping an additional 2 mm Hg and then starting to rise, 9 PLH were collected aloft (Fig. 4A, Table 1). During the next 42 h, the pressure increased to 763 mm Hg. before starting to drop 6 h before the evening PLH activity period. Only
two PLH were captured aloft on 31 August (Fig. 4B, Table 1). The pressure rose slightly, then declined 3 mm Hg to 759.5 mm Hg over the next 18 h and the pressure continued to drop during the evening activity period. A total of 15 PLH were collected aloft during the sampling on 1 September (Fig. 4B, Table 1). The barometric pressure continued to drop 5 mm Hg over the next 24 h, rise slightly during the evening activity period and 8 PLH were collected aloft during the evening sampling on 2 September (Fig. 4C. Table 1). Over the next 40 h, the barometric pressure rose 11 mm Hg from 755 mm Hg to 766 mm Hg before declining 2.5 mm Hg in the 6 h before a PLH evening activity period. Under the influence of rising pressure (3–4 September) no sampling flights were taken due to RPV mechanical difficulties, so PLH activity aloft during those evenings is unknown but on the evening of 5 September under falling pressure, 12 PLH were collected aloft (Fig. 4D, Table 1). Barometric pressure continued to drop 6.6 mm of Hg to 757 m Hg over the next 24 h. A total of 18 PLH were collected aloft on the evening of 6 Sept. RPV mechanical difficulties
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Fig. 4. Comparison of barometric pressure with aerial RPV collections during the duration of the aerial sampling.
prevented additional aerial sampling until 11 September when the field was cut and a single sampling flight was taken. Prior to the 11 September evening sampling, the barometric pressure had declined 3.6 mm Hg from 762.5 mm Hg to 758.9 mm Hg during the 12 h prior to the sampling flight. A total of 10 PLH were collected during flights on that day.
3. Conclusions A total of eight sampling dates is a very small data set to draw any definitive conclusions on the general environmental cues used by PLH to initiate their fall migration. The evening activity period between 1 h before to 30 min after sunset was consistent regardless of barometric pressure characteristics. PLH adults would
appear around the RPV landing/service area at the same time each night regardless of weather conditions and independent of the aerial capture data, suggesting that falling barometric pressure can be correlated with increased flight activity of diapausing female PLH at ca. 30 m above an alfalfa field. In addition, these data suggest that leafhoppers conditioned to initiate long-range fall migration respond to a drop of barometric pressure lasting >12 h prior to the evening activity period by launching upward into the planetary boundary layer where long-ranged transport occurs. Taylor and Reling (1986) proposed that PLH initiate their return fall migration prior to the arrival of the low pressure front in either calm winds or in winds with a southerly flow. As the leafhoppers are pulled into the front at an upper altitude, they fold their wings in response to air temperatures dropping to <12◦ C and then
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drop out of the front into the warmer air temperatures at lower altitudes behind the front and resume flying. The winds behind the front have a northerly air flow and would transport the leafhoppers southward as long as the leafhoppers remain airborne. Only one of the aerial sampling time periods (31 August) had weather conditions similar to the above described pattern and we collected only two leafhoppers aloft. In contrast, three of the aerial sampling periods occurred just after the passage of a low pressure front and a large number of leafhoppers were collected aloft (29 August – 9 PLH, 2 September – 8 PLH, 6 September – 18 PLH). Two of the sampling periods (1 and 5 September) occurred just after the passage of the highest pressure during the past 24 h and ca. 24 h before the passage of the low pressure front. Under these conditions, large numbers of leafhoppers were flying aloft as reflected in the aerial collection data (1 September – 15 PLH, 5 September – 12 PLH). We believe that PLH in reproductive diapause within a physiological window shortly after eclosion become conditioned to initiate their fall return migratory flight during their normal dusk activity period after barometric pressure has been declining for more than 12 h or when declining barometric pressure immediately follows a high pressure ridge passing through the area. Initiating long-ranged movement under either of these conditions would facilitate the efforts of PLH to migrate south to the overwintering area. However, a much larger sampling data base is required to adequately substantiate our conclusions. While the current fleet of 2.4 m RPVs is providing exciting data, the aerial density of potato leafhopper over populated alfalfa fields ranges between 0–4 individuals per 1000 m3 with one individual per 1000 m3 of air typical. The current RPV design requires 30 min sampling time to sieve 5000 m3 and collect between 0–20 leafhoppers with less than 10 collected leafhoppers typical (50% are females). These low numbers of collected leafhoppers exclude any biological study with the captured leafhoppers and only allow conclusions about reproductive status based on dissection. Laboratory verification of reproductive status requires a larger number of females to be collected during each flight and conclusions on flight behavior into the planetary boundary layer could be strengthened with larger collections of individuals in smaller time slices. To solve this problem, we are
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in the final stages of constructing and testing two larger RPVs capable of sampling larger quantities of air per time slice. The 3 m wingspan RPV (5 hp) is estimated to increase the sampling capacity by 50–60% (7500–8000 m3 /30 min) over the currently used design of 2.4 m, while the 4 m wingspan RPV (14 hp) is estimated to increase the sampling capacity by 140–200% (12 000–15 000 m3 /30 min). However, the cost of each RPV rises from about $2500 for the 2.4 m RPV to $6000 for the 3 m RPV and $12 000 for the 4 m RPV.
Appendix A A.1. Assembling a RPV from ‘off the shelf’ components The airframe chosen for the RPV needs to be aerodynamically capable of carrying a reasonable payload aloft and be relatively stable when flying. An airframe in the 2.4 m wing span size meets these criteria and is readily available in both kit form ($130) and 85% pre-built ($240). The Senior Telemaster available from Hobby Lobby International 1 has a 2.38 m wingspan, is of stable design, is easily modified into a durable RPV, and has a payload capacity of 2.7 kg. The standard Sr. Telemaster airframe is strong, but requires modification and strengthening in a few areas. The engine firewall should to be replaced with a piece of 12–13 mm thick plywood (0.5 in) retaining the downthrust angle of the original firewall. The wing main spars should be strengthened by gluing 0.007 carbon fiber tape to the top and bottom of the main wing spars. In addition, the removable dihedral braces need to be replaced with straight pieces of either oak, ash or birch. To assist in takeoff and landing, install 40–50% span slotted flaps on the wings and warp the wings to give 3-degrees washout (upward twist) at the wing tips. The tail wheel bracket should be replaced with a bracket rated to 14 kg plane weight and the wire landing gear replaced with taller composite or aluminum gear to accommodate the 45 cm diameter propeller. Wheel size should be at least 12–13 cm diameter (5 in). 1 Hobby Lobby International, 5614 Franklin Pike Circle, Brentwood, TN 37027; tel.: +1-615-373-1444.
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A.2. Engine and propeller selection: The choice of engine and propeller for the job is a critical decision to insure the success of the RPV as a sampling platform. Initially, it appears that the choices of engine power and fuel sources are numerous but in reality, only one engine manufacturer provides a durable engine with favorable power to thrust ratios, while consuming a reasonable amount of fuel. Most engines available to power miniature aircraft use alcohol based fuels. These engines are light in weight and powerful but are not suited for strenuous RPV flying. High fuel consumption rates, fuel based ignition timing and light-duty construction contribute to less than acceptable engine reliability. Similar engines utilizing kerosene-ether fuels (diesels) have better fuel economy but also have less than acceptable reliability. Most of the available gasoline fueled engines have high fuel consumption rates and poor power to weight ratios which consumes an unacceptable portion of the available payload. The German engine manufacturer, 3 W-Modellmotoren 2 produces a line of gasoline fueled engines which have excellent power to weight thrust ratios and excellent fuel consumption rates. These engines are distributed in the US by Aircraft International Inc. 3 and Cactus Aviation 4 . Their 24 cc engine (the smallest of their engine line) is an excellent choice for a 2.4 m wingspan RPV and only consumes 25 cc of gasoline/min. Propellers need to be matched to the engine power available, the amount of drag present in the airframe, and required air speed. RPVs fitted with ‘high drag’ collectors need to be matched with propellers providing the highest thrust possible while maintaining airspeed. A 45 cm diameter propeller with a 20 cm pitch (18 in × 8 in) or a 50 cm × 20 cm (20 in × 8 in) propeller are excellent matches for the 3 W-24 cc engine mounted on a 2.4 m wingspan RPV. A.3. On-board control systems: The ‘remote control link’ using a radio frequency transmitter and radio signal receiver on board to 2
Hasswiesenstr. 22, 63322 Roedermark, Germany. 8 Country Meadow Dr., Colts Neck, NJ 07722; tel.: +1-732-761-0997. 4 10380 E. Heritage, Tucson, AZ 85730; tel.: +1-520-721-0087. 3
control the RPV is the least reliable link in the entire system. When this link is broken through radio interference, electronic component failure, or battery failure, the out-of-control RPV crashes into surrounding objects or the ground. Out of control crashes usually result in partial or complete destruction of the RPV and the potential for property damage or injury are high. Fortunately, advances in electronics in RC radio systems have made these types of failures less common. Careful and judicious installation of radio equipment with the appropriate level of component redundancy greatly reduces the failure rate of the RPVs. Expensive miniature aircraft like RPVs frequently use dual radio receivers on the same frequency. One receiver will control each side of the aircraft (e.g., right elevator, right aileron controlled by the right receiver, left elevator, left aileron controlled with the left receiver). Other controls such as rudder, flaps and throttle are split between the two receivers. Each receiver has a dedicated battery pack and is optically isolated from the servos it controls, which eliminates unwanted radio frequency (RF) interference entering the receiver through the long wires connecting the receiver to the servos located throughout the airplane. Servos are the precision electric motors which move the airplane’s control surfaces on command from the receiver. Each of the two optical isolator units has its own battery source for the servos it controls. In this arrangement, any component failure on either side of the airplane allows the plane to be landed under reduced control.
A.4. Locating a pilot: Building and flying miniature aircraft is a popular hobby around the world. In the US, organized clubs can be found around most towns and cities of at least moderate size. Learning to fly miniature aircraft requires patience and a time commitment over a couple of years but virtually anybody who puts in the required time to learn can become a successful pilot. Many organized clubs have ‘student pilot programs’ to assist individuals new to the hobby to become proficient pilots and builders. There is, however, another major step between being a proficient pilot of the ‘typical hobby miniature aircraft’ and proficiency in flying high drag, heavily loaded RPVs. The time commitment for a
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non-pilot to gain the skills to reliably pilot a 2.4 m wingspan RPV is significant and would require an intensive time commitment for a minimum of 2 years with high quality instruction. Frequently, the time period is longer. For the researcher wanting to use RPVs as sampling platforms but is deterred by the time commitment to become a competent pilot, a phone call and visit to the local radio control airplane club usually results in the services of one or more proficient pilots who will fly the research RPV for minimum compensation. The closest RC clubs can be located through either Academy of Model Aeronautics 5 (AMA) or Sport Flyers of America 6 . A.5. Liability insurance An out-of-control RPV, weighing in excess of 10 kg, outfitted with a propeller spinning in excess of 8000 rpm, powered with an engine producing a minimum of 3 hp and flying at 65 kph is capable of causing considerable property damage, injury, or death to spectators. Liability insurance coverage for the RPV pilot and other individuals associated with the research effort is highly recommended. At the very minimum, the pilot should be a current member of the Academy of Model Aeronautics (AMA). Payment of annual dues (currently US$45) provides the pilot with $2.5 million liability coverage. A second option is membership in the Sport Flyers of America. Membership dues are $40 and liability coverage is $4 million. There are certain safety restrictions to follow for the pilot to be covered with either of these plans. Most university and government agencies have an umbrella liability policy that may also cover the individuals involved in the research effort. Investigate your liability coverage before initiating research using RPVs.
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internal efficacy as a sampling device and the external design to minimize the drag on the RPV. Drag on the RPV needs to be at the minimum during takeoff and landing. Design of a collector may be an ideal project for an engineering student as a special project. In our research, we have constructed spore collectors from plastic soda bottles, which are light in weight, reasonably durable, inexpensive and sample ca. 8 m3 /min (Fig. 1A, B). These collectors use a vertically mounted standard petri-dish in the air stream as a collection surface and are outfitted with a door that can be remotely opened when the collection period needs to be initiated. These collectors have been used successfully for Fusarium graminearum using selective media in the plate, Phytophthora infestans using water agar as the trapping medium in the plate and simulated tobacco blue mold spore, Peronospora tabacina, release using fluorescent dust and rotorod grease coating the plate surface. Currently, the collectors are being redesigned to reduce the excess drag on the RPV during take-off and landing. In our potato leafhopper research where air sampling quantities need to be an order of magnitude greater, we have utilized a 41 cm2 net which folds over the wing for takeoff and landing (Fig. 1C). The mesh of the net, which is the major contributor to drag, is just small enough to sieve out leafhoppers. This net, samples ca. 167 m3 of air/min (Fig. 1D). If the target insect were larger, the net mesh could be made larger and the RPV could sample a greater volume of air due to the lower level of drag. Smaller insects would require a smaller mesh netting and the increased drag would result in a decreased air volume being sampled. As larger RPVs are developed to sample greater air quantities for leafhoppers, dual net deployment will be used to balance the net-related drag and associated stresses on the airframe.
A.6. Sampling devices: The design of a sampling device or collector which matches the needs of the individual research objectives and target organism will be different for each project. When designing your project-specific collector, design considerations need to be made for both the 5 5151 E. Memorial Dr., Muncie, IN 47302; tel.: +1-800-435-9262. 6 PO Box 7993, Haledon, NJ 07508; tel.: +1-800-745-3597.
A.7. Flying during twilight and after dark Many organisms using moving air currents for long-ranged dispersal initiate movement during the late afternoon and early evening hours. Operating an RPV during these periods of low visibility and darkness is a real challenge regardless of altitude. The RPV must be visible from all angles for the pilot to maintain orientation and keep the RPV flying in the
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proper direction and at the correct altitude. Orientation can be maintained with the combination of unique patterns and different light colors. Fortunately, the recent advances in high intensity LED’s (ultra bright) provide a durable, light weight and energy efficient solution to the RPV lighting problem. Currently, the two brightest LED colors are red and yellow. Ultra bright LED’s range in cost from $.50 to several dollars per LED depending on color, size, and brightness. Typically, ca. 2 V with current draws of 20–40 mA are required per LED. A RPV illuminated with 100 LED’s would only require a battery source capable of providing 2 A of electrical current to operate for 1 h. A two-cell rechargeable nickel-cadmium pack rated at 2000 mA would provide sufficient battery power and would weigh less than 250 g. There are two RPV orientations which require instant identification. These orientations are top versus bottom and front versus back. This problem has been solved by using a combination of two different methods. All LED’s facing forward and upward are yellow while all LED’s facing downward and rearward are red. In addition, the array of LED’s on the top of the aircraft are arranged in a different pattern than those mounted on the bottom. The forward facing LED’s are mounted on the engine firewall, leading edge of the wing at the wing tips, and leading edge of the horizontal and vertical stabilizer. These mounting points give the RPV visibility when approaching the pilot and provides the pilot with the critical glide angle when landing. The LED’s facing rearward are mounted on the ends of the wing and horizontal stabilizer. These mounting points provide the ground-based pilot with RPV visibility when the aircraft is flying away from the pilot and provide visual information about the climbing angle. The upward mounted LED’s are arranged in linear patterns oriented 90◦ to the direction of travel. The downward mounted LED’s are grouped together on the wing tips and are arranged in a linear pattern parallel to the direction of travel. At close distances, the pilot can easily distinguish between the colors illuminating the top and the bottom of the RPV. As the distance increases between the aircraft and the pilot, the colors become harder to differentiate and the pilot becomes more reliant on the illumination pattern. A secondary lighting system needs to be installed on the RPV in the event of primary lighting system failure. A RPV flying without lights after sundown
is impossible to see and control. A few strategically located LED’s powered by an auxiliary battery system and turned on by a remotely controlled switch activated by the pilot allows enough visibility to land the RPV. The critical locations to mount the backup LED’s are the wing’s leading edge and the upper and lower surfaces of the wing. These locations give the pilot the minimum required visual information to land the plane safely. A.8. Scientific instrumentation Complete instrumentation requirements are very project-specific. However, two universally required parameters are airspeed and altitude. Additional parameters could be air temperature and relative humidity. Data can either be recorded on board during the flight and then downloaded upon landing or be transmitted during the flight to the ground in real-time. For example, if accurate altitude is required for the sampling protocol, a real-time telemetry system is required. However, if the sampling protocol requires a record of the altitudes sampled, onboard systems will fill the need less expensively. A real-time telemetry system is available from Aerotelemetry 7 for ca. $2500. This system provides airspeed, altitude, temperature, engine RPM, and onboard battery voltage. The airborne system weighs ca. 500 g. The system’s ground based receiver has a computer interface that allows real-time data collection on a computer hard drive. Additional sensors can be added to the system by the manufacturer. An onboard data recording system can be assembled using the miniaturized TattletaleTM computer (Onset Computer) 8 as the ‘brain’ and various sensors for temperature, airspeed and altitude. This system has the flexibility of multiple sensors to record airspeed within sample collectors rather than estimate airspeed within collectors from a single reading. This option requires a technician with electronic experience and a customized Basic language computer program. However, this system is much lighter and less expensive (ca. $700) than the 7 PO Box 2047, 7471 Talbert Ave., Huntington Beach, CA 92648; tel.: +1-714-596-1342. 8 PO Box 3450, Pocasset, MA 02559-3450; tel.: +1-508-759-9500.
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real-time telemetry system. With the advent of microelectronics, many additional options are available.
A.9. How many RPVs do you need? The number of RPVs needed is dependent on the frequency of sampling required and the total duration of the sampling period. Attrition of aircraft from hard landings, electronic malfunctions, mechanical malfunctions, and airframe stress is a reality. Although many of the malfunctions may be minor, field repair during a sampling event is usually not the best choice. With an experienced pilot, two aircraft are the minimum number required for a sampling protocol comprised of multiple sample collections within a short time period (i.e., several hours). By having 2–3 aircraft available in the field, sampling can continue in the event that minor malfunctions or major damage grounds 1–2 of the aircraft. When the sampling season extends over several weeks, a minimum of three aircrafts should be available because of the very high probability that 1–2 of the aircraft will suffer failure/damage requiring more than several hours of effort to return it to airworthiness (Fig. 1E). In our own research, a minimum of three aircrafts are available before initiating a 2 week sampling protocol requiring six daily flights. Experience has shown that 1–2 aircraft will be disabled, requiring major repair by the end of the 2 week sampling period. If the sampling protocol requires flying under unusual conditions such as turbulence, wind, approaching storm fronts (Fig. 1F), rain, or after sundown, the probability of aircraft attrition increases dramatically. In addition, flying off of marginal runways such as dirt roads or agricultural fields increases the probability of aircraft damage on landing, particularly if the aircraft is heavily loaded with scientific equipment.
References Carlson, J.D., Whalon, M.E., Landis, D.A., 1992. Springtime weather patterns coincident with long-distance migration of potato leafhopper into Michigan. Agric. For. Meteorol. 59, 183– 206. Delong, D.M., 1938. Biological studies on the leafhopper Empoasca fabae as a bean pest. USDA Tech. Bull. 618, 1–3.
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Drake, V.A., Farrow, R.A., 1988. The influence of atmospheric structure and motions on insect migration. Ann. Rev. Entomol. 33, 183–210. Glick, P.A., 1939. The distribution of insects, spiders and mites in the air, USDA Tech. Bull. 673, 150 p. Glick, P.A., 1960. Collecting insects by airplane with special reference to dispersal of the potato leafhopper, USDA Tech. Bull. 1222, 16 p. Gottwald, T.R., Tedders, W.L., 1985. A spore and pollen trap for use on aerial remotely piloted vehicles. Phytopathology 75, 801–807. Gottwald, T.R., Tedders, W.L., 1986. MADDSAP-1, a versatile remotely piloted vehicle for agricultural research. J. Econ. Entomol. 79, 857–863. Huff, F.A., 1963. Relation between leafhopper influxes and synoptic weather conditions. J. Appl. Meteorol. 2, 39–43. Huschke, R.E., 1989. Glossary of Meteorology. American Meteorological Society, 5th edn., 638 p. Isard, S.A., Irwin, M.E., Hollinger, S.E., 1990. Vertical distribution of aphids (Homoptera: Aphididae) in the planetary boundary layer. Environ. Entomol. 19, 1473–1484. Lamp, W.O., Morris, M.J., Armbrust, E.J., 1989. Empoasca (Homoptera: Cicadellidae) abundance and species composition in habitats proximate to alfalfa. Environ. Entomol. 18, 423–428. McDonald, G., Farrow, R.A., 1988. Migration and dispersal of the Rutherglen bug, Nysius vinitor Bergroth (Hemiptera: Lygaeidae) in eastern Australia. Bull. Entomol. Res. 78, 493–510. Medler, J.T., 1957. Migration of the potato leafhopper – a report on a cooperative study. J. Econ. Entomol. 50, 493–497. Medler, J.T., 1962. Long-range displacement of Homoptera in the Central United States. 11th International congress of Entomology, Vienna (1960) 3, 30–36. Pienkowski, R.L., Medler, J.T., 1964. Synoptic weather conditions associated with long-ranged movement of the potato leafhopper, Empoasca fabae, into Wisconsin. Annals. Ent. Soc. Am. 57, 588–591. Poos, F.W., Wheeler, N.H., 1943. Studies on host plants of the leafhoppers of the genus Empoasca. USDA Tech. Bull. 850, 43–44. Poos, F.W., Wheeler, N.H., 1949. Some additional host plants of three species of leafhoppers of the genus Empoasca (Homoptera: Cicadellidae). Proc. Entomol. Soc. Wash. 57, 35– 38. Reling, D., Taylor, R.A.J., 1984. A collopsible tow net used for sampling arthropods by airplane. J. Econ. Entomol. 77, 1615– 1617. Scott, R.W., Achtemeier, G.L., 1987. Estimating pathways of migrating insects carried in atmospheric winds. Environ. Entomol. 16, 1244–1254. Taylor, P.S., Shields, E.J., 1995a. Development of migrant source populations of the potato leafhopper (Harris) (Homoptera: Cicadellidae). Environ. Entomol. 24, 1115–1121. Taylor, P.S., Shields, E.J., 1995b. Phenology of Empoasca fabae (Harris) (Homoptera: Cicadellidae). Environ. Entomol. 24, 1096–1108. Taylor, P.S., Hayes, J.L., Shields, E.J., 1992. Demonstration of pine feeding by Empoasca fabae (Harris) (Homoptera: Cicadellidae) using an elemental marker. J. Kans. Ent. Soc. 66, 250–252.
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Taylor, P.S., Shields, E.J., Tauber, M.J., Tauber, C.A., 1995a. Induction of reproductive diapause in Empoasca fabae (Homoptera: Cicadellidae) and its implications regarding southward migration. Environ. Entomol. 24, 1086–1095. Taylor, P.S., Shields, E.J., Davis, J.I., 1995b. Empoasca fabae (Harris) (Homoptera: Cicadellidae) identification and population studies using allozyme electrophoresis. Environ. Entomol. 24, 1109–1114. Taylor, R.A.J., 1985. Migratory behavior in the Auchenorrhyncha. In: Nault, L.R., Rodriguez, J.G. (Eds.), The Leafhoppers and Planthoppers. Wiley, pp. 259–288
Taylor, R.A.J., Reling, D., 1986. Preferred wind direction of long-distance leafhopper (Empoasca fabae) migrants and its relevance to the return migration of small insects. J. An. Ecol. 55, 1103–1114. Tedders, W.L., Gottwald, T.R., 1986. Evaluation of an insect collecting system and an ultra-low-volume spray system on a remotely piloted vehicle. J. Econ. Entomol. 79, 709–713. Wellington, W.G., 1945a. Conditions governing the distribution of insects in the free atmosphere. Can. Entomol. 78, 7–15. Wellington, W.G., 1945b. Conditions governing the distribution of insects in the free atmosphere. Can. Entomol. 78, 21–28.
Fall migratory flight initiation of the potato leafhopper, Empoasca fabae (Homoptera: Cicadellidae): observations in thelower atmosphere using remote piloted vehicles Elson J. Shields ∗ , A.M. Testa Department of Entomology, 4144 Comstock Hall, Cornell University, Ithaca, NY 14853, USA Accepted 21 July 1999
Abstract The development and use of a remote piloted vehicle (RPV) to sample the lower atmosphere for potato leafhopper has shown a correlation between declining barometric pressure associated with the approach of a weather front and the presence of diapausing leafhoppers 30 m above an alfalfa field initiating their fall migration to the southern states. Population decline of leafhoppers in the source field was also correlated with the passage of weather fronts. The RPV utilized in this research had a 2.4 m wingspan and was outfitted with a fine mesh 41 cm2 insect net. This RPV sampled 167 m3 /min with flight durations of 30 min ©1999 Elsevier Science B.V. All rights reserved. Keywords: Potato leafhopper; Empoasca fabae; Remote piloted vehicle; Aircraft; Aerial sampling; Migration
1. Introduction The potato leafhopper, Empoasca fabae (Harris) (Homoptera: Cicadellidae), has been recognized as a serious pest of many crops in the United states since the mid-1800s (Delong, 1938). This insect is highly polyphagous, capable of successful reproduction on over 200 plant species in 25 different families (Poos and Wheeler, 1943, 1949; Lamp et al., 1989). Potato leafhopper is clearly a migratory insect which overwinters in the southern US (Taylor et al., 1992; Taylor and Shields, 1995a), migrates northward each spring utilizing the spring weather systems (Medler, 1957; Huff, 1963; Pienkowski and Medler, 1964; Carlson et al., 1992; Taylor and Shields, 1995b), ∗ Corresponding author.: Tel.: +1-607-255-8428; fax: +1-607-255-0939 E-mail address: [email protected] (E.J. Shields)
and returns in the fall to the overwintering area in reproductive diapause, assisted by the movement of the fall weather systems (Taylor and Reling, 1986; Taylor et al., 1995a). The lack of genetic variation between widely separated populations, both spatially and temporally, supports the hypothesis that potato leafhopper has an annual circular migration (Taylor et al., 1995b). Once initiated, long-distance leafhopper migration appears to be passive in nature (Medler, 1962; Taylor, 1985). This is typical for migratory movement occurring above the first few meters of the atmosphere, and is a consequence of insect airspeed generally being much less than the speed of the wind (Drake and Farrow, 1988). Migrating leafhoppers have been collected at heights as great as 1220 m (Glick, 1939, 1960) and leafhoppers maintaining this altitude may be transported approximately 30% faster than leafhoppers at 300 m above ground level (AGL) (Pienkowski and Medler, 1964), and in a direction which would
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differ according to prevailing environmental conditions (Scott and Achtemeier, 1987). Limits on the altitudes at which leafhoppers will be transported are imposed by the vertical temperature structure of the atmosphere. Wellington (1945a) found leafhoppers in flight folded their wings when the surrounding air temperature dropped below a flight termination temperature threshold. This wing folding causes the insect to drop until air temperatures above the flight initiation threshold are encountered, or flight is terminated at the ground (Taylor and Reling, 1986; Wellington, 1945b). Taylor and Reling (1986) reported that the highest numbers of potato leafhoppers were trapped when the air temperature exceeded 15◦ C and all potato leafhopper trapping ended when the temperature dropped below 12◦ C. A critical factor to understanding potato leafhopper migration is the suite of environmental cues which initiate the flight activity ultimately resulting in migration. Taylor (1985) reports that potato leafhoppers show strongly crepuscular flight behavior, and that substantially more activity occurs during the evening flight period. McDonald and Farrow (1988) observed that the migration initiation of Nysius vinitor Bergroth (Hemiptera: Lygaeidae) corresponded with the disturbed weather associated with prefrontal airflows. This behavior suggests that falling barometric pressure influences migration initiation for this insect. Research focused on identifying the key environmental and physiological factors triggering the initiation of migration requires that individual leafhoppers be collected in the lower atmosphere shortly after the initiation of migration to allow a comparison of emigrating individuals to the population of leafhoppers in the source area or field. Sampling the lower atmosphere for insects and other biota has always been a challenging task for aerobiologists. Scientists frequently use sampling devices located on the ground with tall chimneys, on the roofs of buildings or attached to towers, balloons, and blimps in an attempt to sample in the lower ca. 100 m of the atmosphere for biota. The deployment of stationary traps is often limited by the distribution of suitable objects on which to mount them (i.e., roofs of tall buildings, communication towers) where permission to locate traps may be difficult to obtain, and the sampling efficiency of these traps may be adversely affected by the disruptive air turbulence caused by the
presence of the building or tower. In most cases, the sampling capacity of the device is directly dependent on the surrounding wind speed and the efficiency of the device may be quite variable over the wide range of wind speeds encountered. In addition, many of these devices have limited usefulness when wind speeds exceed 7 m/s, and have low sampling rates. Mobile sampling devices are usually mounted on manned aircraft (light aircraft, helicopters) for the atmosphere above 152 m AGL (FAA lower limit for flight) and provides sampling for the planetary boundary layer (Glick, 1939, 1960; Reling and Taylor, 1984; Isard et al., 1990). These aircraft-mounted devices provide the flexibility of sampling large quantities of air at any altitude above 152 m. Operation of aircraft requires a certified pilot and usually have operating costs in excess of $100/h. Modification to the airframe for attaching of nets or other sampling devices requires FAA approval with the aircraft subsequently designated as an experimental aircraft. An experimental aircraft designation is usually coupled with increased insurance rates and other use limitations. For safety reasons, sampling the lower atmosphere with manned aircraft is limited to time periods with low levels of turbulence and vertical wind shear. Because the transition zone between the surface boundary layer and the planetary boundary layer is generally considered to be 2–2.5 times the crop canopy height in agricultural settings (Huschke, 1989), sampling the atmosphere for biota between 0–152 m is critical to the understanding of long-range transport initiation for organisms. This depth (0–152 m altitude) is the transition zone between insects and other biota in the local dispersal mode and insects and other biota escaping the surface boundary layer into the faster moving air of the planetary boundary layer to disperse long distances. Remote piloted vehicles (RPVs) outfitted with nets or other sampling devices can safely operate within this transition zone (30–150 m) in turbulent conditions with wind speeds between 0–15 m/s (Gottwald and Tedders, 1985, 1986; Tedders and Gottwald, 1986). With air speeds of ca. 20 m/s and greater, RPVs offer air sampling independent of surrounding wind speed and sampling capacities significantly greater than most fixed location sampling devices. Operational costs are also significantly less than manned aircraft. RPVs of moderate size (2.5–4 m wingspans) could be used to
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collect biota within the transition zone if the aerial density of the target organism overlaps the air sampling capacity of the RPVs. The aerial density of the target organism dictates the volume of air that must be sampled per sampling period and the maximum air sampling capacity of the sampling platform (RPV) strongly influences the duration of the sampling period and the time series resolution of the aerial samples. Larger, more powerful and more expensive RPVs can sample larger quantities of air per unit time and result in more of the target organism or a finer time series resolution to characterize fluctuations in the aerial densities of the target organism. While the aerial density of organisms widely fluctuates and is often unknown, our research results using RPVs indicate the aerial density of Fusarium graminearum ascospores range from 0 to 1000 spores per 1000 m3 of air sampled with 30 ascospores per 1000 m3 typical. This range of aerial densities was measured during May–June within an agricultural region in central New York and include data collected over source areas (agricultural fields) and forested areas at least 1 km from the nearest agricultural field. Aerial density of potato late blight, Phytophthora infestans sporangia, ranges from 0 to 1000 sporangia per 1000 m3 of air sampled with 200–400 sporangia per 1000 m3 typical. Aerial collections were made ca. 60 m above a late blight infested potato field. The aerial density of insects over alfalfa fields during late summer in the late afternoon – early evening at 30–50 m altitude range from 0 to 60 individuals per 1000 m3 of air sampled with 5 insects per 1000 m3 typical. In these collections, the aerial density of potato leafhopper, Empoasca fabae, the target organism never exceeded 2 per 1000 m3 with 0.4 leafhoppers per 1000 m3 typical. These densities were similar to densities reported by Taylor and Reling (1986) towing nets from a small plane at ca. 152 m in altitude. Similar RPV collections during the summer months over mixed hardwood forest yielded an average aerial density of 3.7 insects per 1000 m3 . Researchers from the University of Illinois, using collection pods mounted on a full sized manned helicopter, report aerial density of insects within clear air radar echo seldom exceeding 30 insects per 1000 m3 of air sampled with fewer than 5 insects per 1000 m3 typical. Aphids, the target insect, seldom exceeded
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20 individuals per 1000 m3 with 3 individuals per 1000 m3 a more typical occurrence (Isard et al., 1990). These data indicate that the aerial density of fungal spores and insects frequently differ by one order of magnitude. Therefore, aerial density presents a different set of problems for each organism and requires a RPV designed specifically for the task. 1.1. Designing a RPV for aerobiological sampling: An RPV capable of sampling 160 m3 /min (5000 m3 / 30 min) is relatively easy to assemble using ‘off the shelf; components with a total cost of approximately $2500/vehicle (Appendix A). A 50% increase in air sampling capacity (240 m3 /min) more than doubles the cost of the basic RPV, due to a more costly engine and extensive modifications to airframes to tolerate the additional weight and stresses from the additional air sampling capacity. The RPVs with an engine capable of sampling ca. 500 m3 /min require custom built airframes with wing spans increasing to nearly 4 m (from 2.4 m) and take-off weights increase to 25 kg (up from 10 kg) with a cost that can easily exceed $10 000/RPV. These costs are for the basic RPV without instrumentation. Generally speaking, larger RPVs have more flexible payload capacities for items not required for the direct operation of the RPV. For example, a RPV with a 1.75 m (70 in) wingspan has a useful payload capacity of 1–1.5 kg. A RPV with a 2.4 m (96 in) wingspan has a useful payload capacity of 2.5–2.7 kg while a RPV with a 4 m (144 in) wingspan would have a useful payload of 4–5 kg. Wing loading of RPVs in this size range need to remain below 11 kg/m2 of wing area. The amount of fuel required for a given sampling period has a direct impact on the payload capacity that could be used for sampling devices and instrumentation. 2. Research example: use of RPV to collect potato leafhopper initiating fall migration 2.1. Methods and materials In both 1997 and 1998, an alfalfa field was located with a large potato leafhopper (PLH) population. Sweep net collections of potato leafhoppers were made
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Fig. 1. (A) Aerial spore trap constructed from soda bottles. (B) RPV aloft with sample bottles open. (C) RPV with insect net closed for takeoff and landing (D) RPV with insect net open aloft. (E) RPV with a disabling structural problem. (F) Aerial sampling for potato leafhopper as a weather front approaches.
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Fig. 2. Field populations of potato leafhopper in 1997 and 1998. Weekly collections were separated by nymphal lifestage, adults sexed and females were dissected for the presence of eggs.
three times per week starting in mid-August and continuing until late-September. Each sample was sorted by nymphal instar and the adults were separated by sex. All females were dissected for the presence of eggs. In 1998, daily flights with a net-equipped remote piloted vehicle (2.4 m wingspan) (Fig. 1C, D) were used to collect adult leafhoppers flying 20–40 m above the alfalfa field. Sampling flights were 30 min in duration with an average of 5000 m3 sampled during each flight. Flights were initiated on 28 August and terminated on 6 September. The initial flight was taken each day at 5 p.m. and the final flight was taken after dark usually ending around 8 : 30 p.m. All leafhoppers captured aloft were sexed and the females were dissected for the presence of eggs. Prior to each flight, air temperature, relative humidity, cloud cover and wind observations were recorded.
Each year, barometric pressure was continually recorded for the duration of the study, and daily weather maps illustrating the presence of weather fronts were printed and stored for historical comparisons with sweep net and aerial capture data. In both years, individual male leafhoppers were collected from the field population to verify that the field population was E. fabae.
2.2. Results and discussion Field populations of PLH were very high in both 1997 and 1998, with all life stages present in the field at the start of the study (Fig. 2A, C). Newly emerged adults were always present in the field as each nymphal stage matured. In both years, adult field populations
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Table 1 Potato leafhopper aerial sampling log Date (1998)
Collection Relative time humidity
Temperature Barometric Sunset pressure (mm/Hg)
28 August
5 : 45 p.m. 7 : 00 p.m. 8 : 00 p.m. 6 : 00 p.m. 7 : 00 p.m. 8 : 00 p.m. 9 : 00 p.m. 6 : 00 p.m. 7 : 30 p.m. 8 : 30 p.m. 9 : 00 p.m. 5 : 45 p.m. 6 : 44 p.m. 7 : 25 p.m. 7 : 45 p.m. 8 : 31 p.m. 5 : 45 p.m.
55% 70% 75% 85% 85% 100% 100% 60% 80% 85% 85% 50% 50% 60% 60% 70% 80%
29◦ C 27◦ C 23◦ C 25◦ C 23◦ C 19◦ C 18◦ C 24◦ C 21◦ C 17◦ C 17◦ C 24◦ C 23◦ C 18◦ C 18◦ C 16◦ C 21◦ C
760.73 760.73 760.48 758.95 758.95 759.21 759.46 761.75 761.75 762.25 762.76 761.49 761.49 761.49 761.49 761.49 754.38
0 7 : 52 p.m. 0 0 0 7 : 50 p.m. 1 2 1 0 7 : 45 p.m. 1 0 0 0 4 7 : 42 p.m. 3 2 0 0
0 0 0 0 1 3 1 0 1 0 0 0 2 2 2 0 0
7 : 05 p.m. 7 : 22 p.m. 7 : 50 p.m. 5 September 6 : 00 p.m. 7 : 00 p.m. 7 : 30 p.m. 6 September 6 : 00 p.m. 7 : 15 p.m. 11 September 6 : 47 p.m.
85% 90% 90% 55% 55% 70% 60% 60% 70%
18◦ C 17◦ C 15◦ C 24◦ C 23◦ C 20◦ C 29◦ C 28◦ C 24◦ C
754.63 754.63 754.63 763.78 763.78 763.78 757.17 757.17 758.70
0 7 : 39 p.m. 2 0 1 3 7 : 31 p.m. 2 0 7 : 29 p.m. 8 7 : 23 p.m. 5
1 5 0 0 5 1 0 10 5
29 August
31 August
1 September
2 September
showed major declines with the passage of weather fronts (Fig. 2B, D), but the adult population levels rebounded with the maturation of late instar nymphs. In 1997, the majority of leafhoppers had departed from the field by 19 September. In 1998, the field was cut on 11 September and the study was terminated. In both years, data suggest that oviposition had diminished to a very low level prior to the initiation of field sampling. These results are consistent with the presence of late summer reproductive diapause reported by Taylor et al. (1995a). The data also support the idea that newly emerged adults leave the field shortly after eclosion, and the decline of the adult population after the passage of a weather front suggests that the two events are related. In 1998, a total of 76 leafhoppers were captured aloft with the use of RPVs. Forty of the individuals were females and upon dissection, no eggs were
Male versus female PLH caught
Observations
clear skies, winds calm clear, winds calm lightly overcast clear, winds calm clear, winds calm clear, winds calm clear, winds calm clear, winds from the west 10–15 mph clear, winds from the west 10–15 mph clear, winds from the west 10–15 mph clear and calm scattered clouds, winds calm upper layer clouds, calm hazy skies, calm hazy and calm clear skies and calm thunderstorm passed through 1 h earlier now fairly clear, NW winds 5–10 mph upper level clouds, calm mostly clear and calm clear and calm clear and calm mostly clear and calm clear, west wind 5–10 mph clear, west wind 5–10 mph clear, gusts 5–10 mph
present in any individual, suggesting that all the females captured aloft were in reproductive diapause (Table 1, Fig. 3). Most individual leafhoppers were alive after the completion of a 30 min collection flight, but the laboratory verification of reproductive diapause was not attempted due to the relatively low number of collected individuals. All collected males were identified as E. fabae. Whenever possible, the initial evening flight was taken between 2 and 1.5 h before sunset. Leafhoppers were never collected during flights in this time period. On one occasion late in the season (5 September), the initial flight was taken 1.5–1 h before sunset and a single leafhopper was caught (Table 1). The largest numbers of PLH were collected aloft during the time period of sunset ±30 min. The aerial samples indicated that the PLH activity period leading to flight into the planetary boundary layer where long range transport
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Fig. 3. Potato leafhoppers collected aloft with a remote piloted vehicle (RPV) during 30 min collection flights sampling ca. 5000 m3 of air during the sampling period.
occurs, starts approximately 1 h before sunset and ends approximately 30 min after sunset. In our study, 95% of the leafhoppers caught aloft ca. 30 m above the alfalfa field were flying during this time period (Table 1). These aerial collection data support observations reported by Taylor and Reling (1986) that aerial densities of PLH at 152 m are the highest at 20 min after sunset. When barometric pressure changes are compared to the number of PLH captured aloft, data suggests that PLH migratory flight is correlated with declining barometric pressure prior to the normal PLH evening activity period around sunset. On 28 August, the barometric pressure was dropping just prior to the aerial sampling period and no PLH were collected aloft (Fig. 4A, Table 1). The pressure had dropped 4.8 mm Hg in the previous 18 h. However, on 29 August with the pressure dropping an additional 2 mm Hg and then starting to rise, 9 PLH were collected aloft (Fig. 4A, Table 1). During the next 42 h, the pressure increased to 763 mm Hg. before starting to drop 6 h before the evening PLH activity period. Only
two PLH were captured aloft on 31 August (Fig. 4B, Table 1). The pressure rose slightly, then declined 3 mm Hg to 759.5 mm Hg over the next 18 h and the pressure continued to drop during the evening activity period. A total of 15 PLH were collected aloft during the sampling on 1 September (Fig. 4B, Table 1). The barometric pressure continued to drop 5 mm Hg over the next 24 h, rise slightly during the evening activity period and 8 PLH were collected aloft during the evening sampling on 2 September (Fig. 4C. Table 1). Over the next 40 h, the barometric pressure rose 11 mm Hg from 755 mm Hg to 766 mm Hg before declining 2.5 mm Hg in the 6 h before a PLH evening activity period. Under the influence of rising pressure (3–4 September) no sampling flights were taken due to RPV mechanical difficulties, so PLH activity aloft during those evenings is unknown but on the evening of 5 September under falling pressure, 12 PLH were collected aloft (Fig. 4D, Table 1). Barometric pressure continued to drop 6.6 mm of Hg to 757 m Hg over the next 24 h. A total of 18 PLH were collected aloft on the evening of 6 Sept. RPV mechanical difficulties
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Fig. 4. Comparison of barometric pressure with aerial RPV collections during the duration of the aerial sampling.
prevented additional aerial sampling until 11 September when the field was cut and a single sampling flight was taken. Prior to the 11 September evening sampling, the barometric pressure had declined 3.6 mm Hg from 762.5 mm Hg to 758.9 mm Hg during the 12 h prior to the sampling flight. A total of 10 PLH were collected during flights on that day.
3. Conclusions A total of eight sampling dates is a very small data set to draw any definitive conclusions on the general environmental cues used by PLH to initiate their fall migration. The evening activity period between 1 h before to 30 min after sunset was consistent regardless of barometric pressure characteristics. PLH adults would
appear around the RPV landing/service area at the same time each night regardless of weather conditions and independent of the aerial capture data, suggesting that falling barometric pressure can be correlated with increased flight activity of diapausing female PLH at ca. 30 m above an alfalfa field. In addition, these data suggest that leafhoppers conditioned to initiate long-range fall migration respond to a drop of barometric pressure lasting >12 h prior to the evening activity period by launching upward into the planetary boundary layer where long-ranged transport occurs. Taylor and Reling (1986) proposed that PLH initiate their return fall migration prior to the arrival of the low pressure front in either calm winds or in winds with a southerly flow. As the leafhoppers are pulled into the front at an upper altitude, they fold their wings in response to air temperatures dropping to <12◦ C and then
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drop out of the front into the warmer air temperatures at lower altitudes behind the front and resume flying. The winds behind the front have a northerly air flow and would transport the leafhoppers southward as long as the leafhoppers remain airborne. Only one of the aerial sampling time periods (31 August) had weather conditions similar to the above described pattern and we collected only two leafhoppers aloft. In contrast, three of the aerial sampling periods occurred just after the passage of a low pressure front and a large number of leafhoppers were collected aloft (29 August – 9 PLH, 2 September – 8 PLH, 6 September – 18 PLH). Two of the sampling periods (1 and 5 September) occurred just after the passage of the highest pressure during the past 24 h and ca. 24 h before the passage of the low pressure front. Under these conditions, large numbers of leafhoppers were flying aloft as reflected in the aerial collection data (1 September – 15 PLH, 5 September – 12 PLH). We believe that PLH in reproductive diapause within a physiological window shortly after eclosion become conditioned to initiate their fall return migratory flight during their normal dusk activity period after barometric pressure has been declining for more than 12 h or when declining barometric pressure immediately follows a high pressure ridge passing through the area. Initiating long-ranged movement under either of these conditions would facilitate the efforts of PLH to migrate south to the overwintering area. However, a much larger sampling data base is required to adequately substantiate our conclusions. While the current fleet of 2.4 m RPVs is providing exciting data, the aerial density of potato leafhopper over populated alfalfa fields ranges between 0–4 individuals per 1000 m3 with one individual per 1000 m3 of air typical. The current RPV design requires 30 min sampling time to sieve 5000 m3 and collect between 0–20 leafhoppers with less than 10 collected leafhoppers typical (50% are females). These low numbers of collected leafhoppers exclude any biological study with the captured leafhoppers and only allow conclusions about reproductive status based on dissection. Laboratory verification of reproductive status requires a larger number of females to be collected during each flight and conclusions on flight behavior into the planetary boundary layer could be strengthened with larger collections of individuals in smaller time slices. To solve this problem, we are
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in the final stages of constructing and testing two larger RPVs capable of sampling larger quantities of air per time slice. The 3 m wingspan RPV (5 hp) is estimated to increase the sampling capacity by 50–60% (7500–8000 m3 /30 min) over the currently used design of 2.4 m, while the 4 m wingspan RPV (14 hp) is estimated to increase the sampling capacity by 140–200% (12 000–15 000 m3 /30 min). However, the cost of each RPV rises from about $2500 for the 2.4 m RPV to $6000 for the 3 m RPV and $12 000 for the 4 m RPV.
Appendix A A.1. Assembling a RPV from ‘off the shelf’ components The airframe chosen for the RPV needs to be aerodynamically capable of carrying a reasonable payload aloft and be relatively stable when flying. An airframe in the 2.4 m wing span size meets these criteria and is readily available in both kit form ($130) and 85% pre-built ($240). The Senior Telemaster available from Hobby Lobby International 1 has a 2.38 m wingspan, is of stable design, is easily modified into a durable RPV, and has a payload capacity of 2.7 kg. The standard Sr. Telemaster airframe is strong, but requires modification and strengthening in a few areas. The engine firewall should to be replaced with a piece of 12–13 mm thick plywood (0.5 in) retaining the downthrust angle of the original firewall. The wing main spars should be strengthened by gluing 0.007 carbon fiber tape to the top and bottom of the main wing spars. In addition, the removable dihedral braces need to be replaced with straight pieces of either oak, ash or birch. To assist in takeoff and landing, install 40–50% span slotted flaps on the wings and warp the wings to give 3-degrees washout (upward twist) at the wing tips. The tail wheel bracket should be replaced with a bracket rated to 14 kg plane weight and the wire landing gear replaced with taller composite or aluminum gear to accommodate the 45 cm diameter propeller. Wheel size should be at least 12–13 cm diameter (5 in). 1 Hobby Lobby International, 5614 Franklin Pike Circle, Brentwood, TN 37027; tel.: +1-615-373-1444.
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A.2. Engine and propeller selection: The choice of engine and propeller for the job is a critical decision to insure the success of the RPV as a sampling platform. Initially, it appears that the choices of engine power and fuel sources are numerous but in reality, only one engine manufacturer provides a durable engine with favorable power to thrust ratios, while consuming a reasonable amount of fuel. Most engines available to power miniature aircraft use alcohol based fuels. These engines are light in weight and powerful but are not suited for strenuous RPV flying. High fuel consumption rates, fuel based ignition timing and light-duty construction contribute to less than acceptable engine reliability. Similar engines utilizing kerosene-ether fuels (diesels) have better fuel economy but also have less than acceptable reliability. Most of the available gasoline fueled engines have high fuel consumption rates and poor power to weight ratios which consumes an unacceptable portion of the available payload. The German engine manufacturer, 3 W-Modellmotoren 2 produces a line of gasoline fueled engines which have excellent power to weight thrust ratios and excellent fuel consumption rates. These engines are distributed in the US by Aircraft International Inc. 3 and Cactus Aviation 4 . Their 24 cc engine (the smallest of their engine line) is an excellent choice for a 2.4 m wingspan RPV and only consumes 25 cc of gasoline/min. Propellers need to be matched to the engine power available, the amount of drag present in the airframe, and required air speed. RPVs fitted with ‘high drag’ collectors need to be matched with propellers providing the highest thrust possible while maintaining airspeed. A 45 cm diameter propeller with a 20 cm pitch (18 in × 8 in) or a 50 cm × 20 cm (20 in × 8 in) propeller are excellent matches for the 3 W-24 cc engine mounted on a 2.4 m wingspan RPV. A.3. On-board control systems: The ‘remote control link’ using a radio frequency transmitter and radio signal receiver on board to 2
Hasswiesenstr. 22, 63322 Roedermark, Germany. 8 Country Meadow Dr., Colts Neck, NJ 07722; tel.: +1-732-761-0997. 4 10380 E. Heritage, Tucson, AZ 85730; tel.: +1-520-721-0087. 3
control the RPV is the least reliable link in the entire system. When this link is broken through radio interference, electronic component failure, or battery failure, the out-of-control RPV crashes into surrounding objects or the ground. Out of control crashes usually result in partial or complete destruction of the RPV and the potential for property damage or injury are high. Fortunately, advances in electronics in RC radio systems have made these types of failures less common. Careful and judicious installation of radio equipment with the appropriate level of component redundancy greatly reduces the failure rate of the RPVs. Expensive miniature aircraft like RPVs frequently use dual radio receivers on the same frequency. One receiver will control each side of the aircraft (e.g., right elevator, right aileron controlled by the right receiver, left elevator, left aileron controlled with the left receiver). Other controls such as rudder, flaps and throttle are split between the two receivers. Each receiver has a dedicated battery pack and is optically isolated from the servos it controls, which eliminates unwanted radio frequency (RF) interference entering the receiver through the long wires connecting the receiver to the servos located throughout the airplane. Servos are the precision electric motors which move the airplane’s control surfaces on command from the receiver. Each of the two optical isolator units has its own battery source for the servos it controls. In this arrangement, any component failure on either side of the airplane allows the plane to be landed under reduced control.
A.4. Locating a pilot: Building and flying miniature aircraft is a popular hobby around the world. In the US, organized clubs can be found around most towns and cities of at least moderate size. Learning to fly miniature aircraft requires patience and a time commitment over a couple of years but virtually anybody who puts in the required time to learn can become a successful pilot. Many organized clubs have ‘student pilot programs’ to assist individuals new to the hobby to become proficient pilots and builders. There is, however, another major step between being a proficient pilot of the ‘typical hobby miniature aircraft’ and proficiency in flying high drag, heavily loaded RPVs. The time commitment for a
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non-pilot to gain the skills to reliably pilot a 2.4 m wingspan RPV is significant and would require an intensive time commitment for a minimum of 2 years with high quality instruction. Frequently, the time period is longer. For the researcher wanting to use RPVs as sampling platforms but is deterred by the time commitment to become a competent pilot, a phone call and visit to the local radio control airplane club usually results in the services of one or more proficient pilots who will fly the research RPV for minimum compensation. The closest RC clubs can be located through either Academy of Model Aeronautics 5 (AMA) or Sport Flyers of America 6 . A.5. Liability insurance An out-of-control RPV, weighing in excess of 10 kg, outfitted with a propeller spinning in excess of 8000 rpm, powered with an engine producing a minimum of 3 hp and flying at 65 kph is capable of causing considerable property damage, injury, or death to spectators. Liability insurance coverage for the RPV pilot and other individuals associated with the research effort is highly recommended. At the very minimum, the pilot should be a current member of the Academy of Model Aeronautics (AMA). Payment of annual dues (currently US$45) provides the pilot with $2.5 million liability coverage. A second option is membership in the Sport Flyers of America. Membership dues are $40 and liability coverage is $4 million. There are certain safety restrictions to follow for the pilot to be covered with either of these plans. Most university and government agencies have an umbrella liability policy that may also cover the individuals involved in the research effort. Investigate your liability coverage before initiating research using RPVs.
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internal efficacy as a sampling device and the external design to minimize the drag on the RPV. Drag on the RPV needs to be at the minimum during takeoff and landing. Design of a collector may be an ideal project for an engineering student as a special project. In our research, we have constructed spore collectors from plastic soda bottles, which are light in weight, reasonably durable, inexpensive and sample ca. 8 m3 /min (Fig. 1A, B). These collectors use a vertically mounted standard petri-dish in the air stream as a collection surface and are outfitted with a door that can be remotely opened when the collection period needs to be initiated. These collectors have been used successfully for Fusarium graminearum using selective media in the plate, Phytophthora infestans using water agar as the trapping medium in the plate and simulated tobacco blue mold spore, Peronospora tabacina, release using fluorescent dust and rotorod grease coating the plate surface. Currently, the collectors are being redesigned to reduce the excess drag on the RPV during take-off and landing. In our potato leafhopper research where air sampling quantities need to be an order of magnitude greater, we have utilized a 41 cm2 net which folds over the wing for takeoff and landing (Fig. 1C). The mesh of the net, which is the major contributor to drag, is just small enough to sieve out leafhoppers. This net, samples ca. 167 m3 of air/min (Fig. 1D). If the target insect were larger, the net mesh could be made larger and the RPV could sample a greater volume of air due to the lower level of drag. Smaller insects would require a smaller mesh netting and the increased drag would result in a decreased air volume being sampled. As larger RPVs are developed to sample greater air quantities for leafhoppers, dual net deployment will be used to balance the net-related drag and associated stresses on the airframe.
A.6. Sampling devices: The design of a sampling device or collector which matches the needs of the individual research objectives and target organism will be different for each project. When designing your project-specific collector, design considerations need to be made for both the 5 5151 E. Memorial Dr., Muncie, IN 47302; tel.: +1-800-435-9262. 6 PO Box 7993, Haledon, NJ 07508; tel.: +1-800-745-3597.
A.7. Flying during twilight and after dark Many organisms using moving air currents for long-ranged dispersal initiate movement during the late afternoon and early evening hours. Operating an RPV during these periods of low visibility and darkness is a real challenge regardless of altitude. The RPV must be visible from all angles for the pilot to maintain orientation and keep the RPV flying in the
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proper direction and at the correct altitude. Orientation can be maintained with the combination of unique patterns and different light colors. Fortunately, the recent advances in high intensity LED’s (ultra bright) provide a durable, light weight and energy efficient solution to the RPV lighting problem. Currently, the two brightest LED colors are red and yellow. Ultra bright LED’s range in cost from $.50 to several dollars per LED depending on color, size, and brightness. Typically, ca. 2 V with current draws of 20–40 mA are required per LED. A RPV illuminated with 100 LED’s would only require a battery source capable of providing 2 A of electrical current to operate for 1 h. A two-cell rechargeable nickel-cadmium pack rated at 2000 mA would provide sufficient battery power and would weigh less than 250 g. There are two RPV orientations which require instant identification. These orientations are top versus bottom and front versus back. This problem has been solved by using a combination of two different methods. All LED’s facing forward and upward are yellow while all LED’s facing downward and rearward are red. In addition, the array of LED’s on the top of the aircraft are arranged in a different pattern than those mounted on the bottom. The forward facing LED’s are mounted on the engine firewall, leading edge of the wing at the wing tips, and leading edge of the horizontal and vertical stabilizer. These mounting points give the RPV visibility when approaching the pilot and provides the pilot with the critical glide angle when landing. The LED’s facing rearward are mounted on the ends of the wing and horizontal stabilizer. These mounting points provide the ground-based pilot with RPV visibility when the aircraft is flying away from the pilot and provide visual information about the climbing angle. The upward mounted LED’s are arranged in linear patterns oriented 90◦ to the direction of travel. The downward mounted LED’s are grouped together on the wing tips and are arranged in a linear pattern parallel to the direction of travel. At close distances, the pilot can easily distinguish between the colors illuminating the top and the bottom of the RPV. As the distance increases between the aircraft and the pilot, the colors become harder to differentiate and the pilot becomes more reliant on the illumination pattern. A secondary lighting system needs to be installed on the RPV in the event of primary lighting system failure. A RPV flying without lights after sundown
is impossible to see and control. A few strategically located LED’s powered by an auxiliary battery system and turned on by a remotely controlled switch activated by the pilot allows enough visibility to land the RPV. The critical locations to mount the backup LED’s are the wing’s leading edge and the upper and lower surfaces of the wing. These locations give the pilot the minimum required visual information to land the plane safely. A.8. Scientific instrumentation Complete instrumentation requirements are very project-specific. However, two universally required parameters are airspeed and altitude. Additional parameters could be air temperature and relative humidity. Data can either be recorded on board during the flight and then downloaded upon landing or be transmitted during the flight to the ground in real-time. For example, if accurate altitude is required for the sampling protocol, a real-time telemetry system is required. However, if the sampling protocol requires a record of the altitudes sampled, onboard systems will fill the need less expensively. A real-time telemetry system is available from Aerotelemetry 7 for ca. $2500. This system provides airspeed, altitude, temperature, engine RPM, and onboard battery voltage. The airborne system weighs ca. 500 g. The system’s ground based receiver has a computer interface that allows real-time data collection on a computer hard drive. Additional sensors can be added to the system by the manufacturer. An onboard data recording system can be assembled using the miniaturized TattletaleTM computer (Onset Computer) 8 as the ‘brain’ and various sensors for temperature, airspeed and altitude. This system has the flexibility of multiple sensors to record airspeed within sample collectors rather than estimate airspeed within collectors from a single reading. This option requires a technician with electronic experience and a customized Basic language computer program. However, this system is much lighter and less expensive (ca. $700) than the 7 PO Box 2047, 7471 Talbert Ave., Huntington Beach, CA 92648; tel.: +1-714-596-1342. 8 PO Box 3450, Pocasset, MA 02559-3450; tel.: +1-508-759-9500.
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real-time telemetry system. With the advent of microelectronics, many additional options are available.
A.9. How many RPVs do you need? The number of RPVs needed is dependent on the frequency of sampling required and the total duration of the sampling period. Attrition of aircraft from hard landings, electronic malfunctions, mechanical malfunctions, and airframe stress is a reality. Although many of the malfunctions may be minor, field repair during a sampling event is usually not the best choice. With an experienced pilot, two aircraft are the minimum number required for a sampling protocol comprised of multiple sample collections within a short time period (i.e., several hours). By having 2–3 aircraft available in the field, sampling can continue in the event that minor malfunctions or major damage grounds 1–2 of the aircraft. When the sampling season extends over several weeks, a minimum of three aircrafts should be available because of the very high probability that 1–2 of the aircraft will suffer failure/damage requiring more than several hours of effort to return it to airworthiness (Fig. 1E). In our own research, a minimum of three aircrafts are available before initiating a 2 week sampling protocol requiring six daily flights. Experience has shown that 1–2 aircraft will be disabled, requiring major repair by the end of the 2 week sampling period. If the sampling protocol requires flying under unusual conditions such as turbulence, wind, approaching storm fronts (Fig. 1F), rain, or after sundown, the probability of aircraft attrition increases dramatically. In addition, flying off of marginal runways such as dirt roads or agricultural fields increases the probability of aircraft damage on landing, particularly if the aircraft is heavily loaded with scientific equipment.
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Taylor, P.S., Shields, E.J., Tauber, M.J., Tauber, C.A., 1995a. Induction of reproductive diapause in Empoasca fabae (Homoptera: Cicadellidae) and its implications regarding southward migration. Environ. Entomol. 24, 1086–1095. Taylor, P.S., Shields, E.J., Davis, J.I., 1995b. Empoasca fabae (Harris) (Homoptera: Cicadellidae) identification and population studies using allozyme electrophoresis. Environ. Entomol. 24, 1109–1114. Taylor, R.A.J., 1985. Migratory behavior in the Auchenorrhyncha. In: Nault, L.R., Rodriguez, J.G. (Eds.), The Leafhoppers and Planthoppers. Wiley, pp. 259–288
Taylor, R.A.J., Reling, D., 1986. Preferred wind direction of long-distance leafhopper (Empoasca fabae) migrants and its relevance to the return migration of small insects. J. An. Ecol. 55, 1103–1114. Tedders, W.L., Gottwald, T.R., 1986. Evaluation of an insect collecting system and an ultra-low-volume spray system on a remotely piloted vehicle. J. Econ. Entomol. 79, 709–713. Wellington, W.G., 1945a. Conditions governing the distribution of insects in the free atmosphere. Can. Entomol. 78, 7–15. Wellington, W.G., 1945b. Conditions governing the distribution of insects in the free atmosphere. Can. Entomol. 78, 21–28.