Field Assessment ofBeauveria bassiana(Balsamo) Vuillemin and Potential Synergism with Diflubenzuron for Control of Savanna Grasshopper Complex (Orthoptera) in Mali

Journal of Invertebrate Pathology 73, 34–39 (1999) Article ID jipa.1998.4804, available online at http://www.idealibrary.com on

Field Assessment of Beauveria bassiana (Balsamo) Vuillemin and Potential Synergism with Diflubenzuron for Control of Savanna Grasshopper Complex (Orthoptera) in Mali Francisco X. Delgado,* James H. Britton,† Jerome A. Onsager,‡ and Will Swearingen* *Department of Entomology, Montana State University, Bozeman, Montana 59717; †Mycotech Corporation, 2500 Continental Drive, Butte, Montana 59701; and ‡USDA, ARS, 1500 N. Central Avenue, Sidney, Montana 59270 Received May 12, 1997; accepted June 29, 1998

serious damage to crops (Maiga, 1992). Concerns over the health and environmental effects of traditional chemical acridid controls (OTA, 1990) have led to the pursuit of biological grasshopper and locust control methods, including the use of entomopathogenic fungi. In search of alternative methods to control grasshoppers and locusts, this group and others have conducted laboratory and field studies to evaluate the biocontrol potential of Beauveria bassiana (Balsamo) Vuillemin, strain GHA. B. bassiana has effectively reduced grasshopper and locust populations in some trials, while in other tests variable results were reported (Lobo-Lima et al., 1992; Johnson et al., 1992; Delgado et al., 1997b; Reuter et al., 1993; Inglis et al., 1997a). Previous reports suggested that Dimilin (Uniroyal Chemical Co., Inc.), a chitin synthesis inhibitor containing the active ingredient diflubenzuron, makes infection by hyphomycete entomopathogens faster and easier. For example, Hassan and Charnley (1989) reported that cuticle of Manduca sexta treated with Dimilin exhibited diminished resistance to invasion by hyphae of Metarhizium anisopliae. A laboratory assay versus a North American grasshopper species showed that a mixture of Dimilin and B. bassiana increased the rate of mortality (Reuter et al., 1996), and an application of B. bassiana and Dimilin to a field population in the United States also suggested that the mixture was efficacious (Foster et al., 1996). The objective of this study was to determine whether low levels of Dimilin could enhance the efficacy of B. bassiana strain GHA in operational-scale tests on unconfined populations of grasshoppers in the Saharo-Sahelian region of Mali.

In large-scale field trials in Mali, formulated conidia of Beauveria bassiana (Balsamo) Vuillemin strain GHA were tested against unconfined grasshopper populations in field plots of 10 ha each. The trials compared B. bassiana conidia formulated in a mineral oil carrier, formulated diflubenzuron, a combination of B. bassiana plus formulated diflubenzuron, and fenitrothion. A total of 30 different species of grasshoppers occurred in the experimental plots, of which 3 were dominant in all plots, namely, Cryptocatantops haemorrhoidalis (Krauss), Acrotylus blondeli (Saussure), and Hieroglyphus daganensis (Krauss). The density of grasshopper populations in the plots was determined by the number of grasshoppers counted in 0.1-m2 rings laid out in repeated transects. All treatments significantly reduced the grasshopper densities in the experimental plots compared to the untreated controls. After 14 days posttreatment the grasshopper populations decreased by 38.1% in plots treated with B. bassiana alone, 29.4% in plots treated with diflubenzuron alone, and 55.6% in plots treated with the B. bassiana plus diflubenzuron. Effects of the diflubenzuron–B. bassiana mixture were additive and not synergistic. In the fenitrothion plots, after a drop of 95.5% within the first 48 h after the treatment, the grasshopper population steadily increased at a rate of 12.4% per day for the remainder of the 14-day period, whereas densities in the other treated plots continued to decrease. These trials suggest that B. bassiana, with or without a diflubenzuron additive, exerts a continuous effect over a prolonged period. r 1999 Academic Press Key Words: Beauveria bassiana; grasshoppers; diflubenzuron; fenitrothion; survival rate; synergist; pathogens.

MATERIALS AND METHODS INTRODUCTION

Conidia Preparations, Formulations, Pesticides, and Application Equipment

In the hot, arid Sahelian and Saharo-Sahelian regions of Mali, damaging infestations of the savanna grasshopper complex occur every year. These grasshopper species can coexist at high densities and cause 0022-2011/99 $30.00 Copyright r 1999 by Academic Press All rights of reproduction in any form reserved.

Dry conidia of B. bassiana GHA strain were produced by Mycotech Corp., Butte, Montana. The two formulations using fungal conidia were B. bassiana conidia 34

ASSESSMENT OF B. bassiana AGAINST GRASSHOPPERS

formulated in a mineral oil (Mycotech carrier) and conidia plus diflubenzuron (Dimilin 2F) formulated in mineral oil. The viability of the conidia averaged 98% at the time of formulation. Formulations were stored at room temperatures ranging from 17 to 35°C in Butte (Montana), Bamako (Mali), and Mourdiah village (Mali) for several months. After the trials, samples of each formulation were checked for viability. Viability then averaged 92%. Diflubenzuron was supplied by Uniroyal Chemical Co., Middlebury, Connecticut, in a flowable formulation, Dimilin 2F (240 g a.i./liter). When sprayed alone, diflubenzuron was mixed with the mineral oil to achieve a volume rate of 2 liters per hectare. The fenitrothion was supplied by Service National de Protection des Ve´ge´taux, Bamako, Mali, in a ultra-low-volume (ULV) formulation, Sumithion 500 ULV (Sumitomo Chemical Co., Ltd.). Treatment Application Rates Treatments were (1) B. bassiana in the oil carrier; (2) diflubenzuron in the oil carrier; (3) B. bassiana plus diflubenzuron in the oil carrier; (4) fenitrothion in a ULV formulation; and (5) an untreated control. Formulated conidia of B. bassiana were applied at the rate of 2.5 ⫻ 1013 spores per hectare at a volume rate of 2 liters per hectare. The recommended field rate of diflubenzuron for rangeland grasshoppers in the United States is 17.5 g/ha (Reuter et al., 1996). For this experiment, diflubenzuron was applied at a rate of 1.75 g per hectare, which corresponds to 1⁄10 of the recommended field rate. This rate of diflubenzuron combined with B. bassiana was effective at killing grasshoppers in laboratory and field tests in the United States (Reuter et al., 1996; Foster et al., 1996). Hassan and Charnley (1989) reported that ‘‘cuticles in dimilintreated insects (Manduca sexta) provide little resistance to penetrant hyphae of Metarhizium anisopliae and fall apart during invasion.’’ The rate of Dimilin used in this experiment represents a low dose that is thought to weaken the target insects, rendering them more susceptible to B. bassiana infection (Foster et al., 1996). Fenitrothion, a chemical pesticide widely used for grasshopper control in Africa, was applied at a rate of 250 g a.i./ha in a volume rate of 0.5 liters per hectare, which is a standard recommended field rate against grasshoppers (Launois-Luong, 1988). Field Plots: Location, Layout, and Design The field experiments were conducted in the Mourdiah region. The savanna grasshopper complex, which is considered of significant economic importance (Maiga, 1992), was selected as the target for testing the fungal pathogen. Plots were arranged in a randomized complete block design with three blocks. Two of the blocks

35

were located 22 km north of Mourdiah along the road to Nara and the third block was located 29 km south of Mourdiah, near the village of Gallo. Treatments were applied to unconfined populations of grasshoppers in field plots of 10 ha each. Each plot consisted of a square of 316 ⫻ 316 m. The experiment was composed of a total of five plots (one for each treatment) in each block, for a total field trial size of 150 ha. A minimum spacing of 30 m was left between plots. The plots were laid out taking into account the dominant wind direction during the spraying period to prevent cross-contamination. Spraying Parameters The formulated products were sprayed onto the plots in swaths perpendicular to the wind direction, when the wind speed ranged between 0.1 to 4 m/s. During the treatments the wind speed averaged 1.3 m/s. All treatments were applied in the mornings between 0630 and 1100 h. Temperatures during treatments ranged from 23 to 31°C and relative humidity between 68 and 98%. Weather data were not collected at other times. Operators were guided by three rows of flaggers at the ends and middle of the plot, with swaths progressing into the wind to keep both operators and flaggers out of the contaminated areas. Treatments were applied with hand-held Micron ULVA-Plus sprayers (Micron Sprayers, Bromyard, Heretfordshire, UK) operated with six alkaline batteries. Spray coverage was confirmed with strips of Ciba–Geigy oil-sensitive paper placed on bare ground and on top of short-grass vegetation. The fenitrothion plots were treated with five operators each carrying one sprayer. All the other plots were sprayed with six operators carrying one sprayer each. Walking speed of the operators was maintained by the use of digital metronomes. Sampling Methods Grasshopper densities were estimated in each plot 1 day before treatment application and for each of 14 days after treatment. The method used 0.1-m2 circular rings in transects of 10 rings spaced 8 m apart (Onsager and Henry, 1977). Six parallel transects (a total of 60 rings) occupying the central area of each plot were used to assure an adequate sample size (Onsager, 1981). Species composition and age structure of the populations were determined from sweep-net samples taken around the rings. One hundred sweep samples from each plot were collected the day before treatment and at 1, 7, and 14 days posttreatment. Analysis To assess treatment effects and the rate of grasshopper population changes, regression procedures were

36

DELGADO ET AL.

used (SAS, 1989). The counts from all transects were averaged to calculate the mean density per square meter in each individual plot, for each day. The density in each treated plot was adjusted for the natural changes that occurred in the untreated control plot within the same block using the formula by Connin and Kuitert (1952)

1

Adjusted Density ⫽ 100 ⫻ 1 ⫺

2,

Ta ⫻ Cb Tb ⫻ Ca

where Tb equals the mean number of grasshoppers counted in the treated plot before the treatment, Ta the mean counted after treatment, Cb the mean count from the untreated control plot before treatment, and Ca the mean count from the untreated control plot after treatment. Preliminary analyses indicated that the variance within different treatments was not equal; therefore, data for each treatment were analyzed separately. The adjusted mean numbers of grasshoppers per square meter were transformed to natural logarithms. Variability between blocks over time was removed with covariance analysis (Steel and Torrie, 1960), and density changes were estimated by regression of log density over time. Exponents of regression coefficients for slope were used to estimate average daily survival rates (Onsager and Hewitt, 1982). RESULTS

Grasshopper populations in all three blocks of the untreated control plots increased gradually through the trial. The population in block one increased from 20.0 to 23.5 grasshoppers per square meter, in block two from 6.67 to 10.0, and block three from 7.3 to 10.3 grasshoppers per square meter. The number of grasshoppers in treated plots, corrected for the changes that occurred in control plots, is presented in Table 1. A total of 30 different species of grasshoppers occurred in the experimental plots, 40% of which hatched within or moved into the plots after the application of the treatments. Among the dominant species in the pretreatment samples, the average percentage of the total initial population was 49.6% for Cryptocatantops haemorrhoidalis (Krauss), 13.7% for Acrotylus blondeli (Saussure), and 4.1% for Hieroglyphus daganensis (Krauss). At the end of the experiment, 16 days later, the percentages of those same species were 22.7, 21.1, and 5.4, respectively. Other species that occurred at important densities, but not in all plots, included Oedaleus senegalensis (Krauss), Ornithacris turbida cavroisis (Finot), Pyrgomorpha cognata (Krauss), Kraussella amabile (Krauss), Diabolocatantops axillaris (Krauss), and Acorypha glaucopsis (Walker). As is evident from Table 2, which portrays the age

TABLE 1 Mean Number of Grasshoppers per Square Meter in Field Plots Treated with Beauveria bassiana, Diflubenzuron, B. bassiana plus Diflubenzuron, and Fenitrothion (Corrected for Natural Changes Occurring in Untreated Control Plots) Days

B. bassiana

B. bassiana/ diflubenzuron

Diflubenzuron

Fenitrothion

⫺1 1 2 3 4 5 6 7 8 9 10 11 12 13 14

9.30 ⫾ 1.59 9.95 ⫾ 1.97 9.55 ⫾ 1.69 12.06 ⫾ (na) 8.78 ⫾ 1.97 8.04 ⫾ 1.83 12.00 ⫾ 5.89 8.32 ⫾ 3.81 6.95 ⫾ 4.15 10.68 ⫾ 6.83 7.63 ⫾ 3.93 7.41 ⫾ 4.38 14.46 ⫾ (na) 5.40 ⫾ 1.23 9.08 ⫾ 5.61

8.23 ⫾ 1.65 6.08 ⫾ 1.00 7.97 ⫾ (na) 6.38 ⫾ 0.72 4.76 ⫾ 0.49 5.59 ⫾ 1.17 4.83 ⫾ 0.83 3.77 ⫾ 0.99 4.09 ⫾ 2.42 2.82 ⫾ 0.81 4.02 ⫾ 0.89 4.37 ⫾ (na) 3.46 ⫾ 0.09 4.53 ⫾ 0.59 2.66 ⫾ 0.40

6.40 ⫾ 0.89 5.07 ⫾ 0.12 8.20 ⫾ 1.29 5.50 ⫾ 0.71 5.33 ⫾ 0.27 6.27 ⫾ 1.58 4.92 ⫾ 1.08 5.77 ⫾ 1.69 3.59 ⫾ 0.13 4.63 ⫾ 0.32 5.10 ⫾ 1.35 4.55 ⫾ 0.36 4.85 ⫾ 0.69 6.05 ⫾ 0.71 3.86 ⫾ 0.61

7.46 ⫾ 1.70 0.39 ⫾ 0.31 0.62 ⫾ 0.22 0.69 ⫾ 0.20 0.46 ⫾ 0.08 0.41 ⫾ 0.17 0.61 ⫾ 0.14 0.87 ⫾ 0.27 0.69 ⫾ 0.17 0.79 ⫾ 0.48 1.59 ⫾ 0.32 1.40 ⫾ 0.64 1.13 ⫾ 0.15 3.36 ⫾ (na) 1.42 ⫾ 0.59

Note. na, The standard error was not calculated because of a single observation for that day.

structure of the populations, hatchings occurred continuously in the experimental plots during the observation period. For the species in the plots, each instar requires an average of about 5 to 8 days for development (see Duranton et al., 1982). All treatments except B. bassiana alone had first instar nymphs at 14 days posttreatment, while second instars at the end of the same period ranged from 17.4 to 25.4% of the sampled population. As reported by Johnson et al. (1992), hatchings and the movements of grasshoppers into plots in this particular region can obscure detection of treatment effects. The use of Connin and Kuitert’s (1952) formula not only minimized experimental error attributable to late hatching and immigration but also allowed treatment responses to be expressed as a proportion of densities that were present at the time of treatment. A knockdown effect was observed in the grasshopper populations following the application of fenitrothion. At 48 h posttreatment, 95.5% control was achieved among the treated populations. However, immediately thereafter, the grasshopper population began to increase in the fenitrothion-treated plots at a rate of 12.4% per day (Fig. 1). In contrast to the fenitrothion-treated plots, the densities in the plots treated with B. bassiana GHA, diflubenzuron, and B. bassiana ⫹ diflubenzuron decreased significantly and continuously through time following treatment. The rates of change (adjusted for changes in control plots) are shown in Table 3. At 14 days posttreatment, the grasshopper populations had decreased by 38.1% in plots treated with B. bassiana

37

ASSESSMENT OF B. bassiana AGAINST GRASSHOPPERS

TABLE 2 Age Structure of Grasshopper Populations in Plots Treated with B. bassiana, Diflubenzuron, B. bassiana plus Diflubenzuron, Fenitrothion, and Untreated Controls as Determined by Sweep Samples Grasshopper stage (percentage ⫾ standard error) Treatment Untreated B. bassiana Diflubenzuron B. bassiana/ diflubenzuron Fenitrothion a b

Day

na

1st instar

2nd instar

3rd instar

4th instar

5th instar

Adults

⫺1 b 14 ⫺1 14 ⫺1 14 ⫺1 14 ⫺1 14

247 260 252 323 202 180 173 126 264 69

29.6 ⫾ 5.7 0.8 ⫾ 1.1 10.7 ⫾ 3.8 0.0 ⫾ 0.0 23.3 ⫾ 5.8 3.3 ⫾ 2.6 15.0 ⫾ 5.3 0.8 ⫾ 1.5 34.5 ⫾ 5.7 7.2 ⫾ 6.1

53.8 ⫾ 6.2 23.8 ⫾ 5.2 62.7 ⫾ 6.0 21.4 ⫾ 4.5 45.0 ⫾ 6.9 25.0 ⫾ 6.3 53.8 ⫾ 7.4 25.4 ⫾ 7.6 50.8 ⫾ 6.0 17.4 ⫾ 8.9

8.9 ⫾ 3.6 53.1 ⫾ 6.1 12.7 ⫾ 4.1 43.0 ⫾ 5.4 15.8 ⫾ 5.0 50.0 ⫾ 7.3 9.2 ⫾ 4.3 32.5 ⫾ 8.2 8.3 ⫾ 3.3 43.5 ⫾ 11.7

4.6 ⫾ 2.7 8.8 ⫾ 3.5 5.6 ⫾ 2.8 25.1 ⫾ 4.7 5.6 ⫾ 3.3 11.7 ⫾ 4.7 11.0 ⫾ 4.7 18.3 ⫾ 6.7 1.9 ⫾ 1.6 10.1 ⫾ 7.1

0.8 ⫾ 1.1 3.8 ⫾ 2.3 2.4 ⫾ 1.9 3.7 ⫾ 2.1 2.5 ⫾ 2.1 2.8 ⫾ 2.4 0.6 ⫾ 1.1 7.9 ⫾ 4.7 0.8 ⫾ 1.0 5.8 ⫾ 5.5

4.9 ⫾ 2.7 9.6 ⫾ 3.6 6.0 ⫾ 2.9 6.8 ⫾ 2.7 7.4 ⫾ 3.6 7.2 ⫾ 3.8 10.4 ⫾ 4.5 15.1 ⫾ 6.2 3.8 ⫾ 2.3 15.9 ⫾ 8.6

n is the total number of grasshoppers sampled in plots from the same treatment. Pretreatment counts taken 1 day prior to treatment application.

GHA alone, 29.4% in plots treated with diflubenzuron alone, and 55.6% in plots treated with the B. bassianaGHA plus diflubenzuron. An expected average daily survival rate (DSR) of 0.9425 can be estimated for the B. bassiana/diflubenzuron treatment as the product of the independent DSRs (i.e., 0.9663 ⫻ 0.9754). Likewise, an expected proportion of control of 0.5635 at 14 days posttreatment can be estimated as 1 ⫺ ((0.9663 ⫻ 0.9754) 14 ). Since both of the expected values for the combination treatment were essentially identical to the observed values (0.9436 and 0.5563, respectively), it is probable that the combined ingredients produced simple additive effects on grasshoppers in the field plots. While the combination of B. bassiana GHA and diflubenzuron significantly increased the rate of density reduction

FIG. 1. Survival in grasshopper populations treated with Beauveria bassiana, diflubenzuron, B. bassiana plus diflubenzuron, and fenitrothion, in Mali (corrected for survival in untreated control plots).

(P ⬍ 0.001), there was no evidence of synergistic enhancement of B. bassiana GHA efficacy by the presence of diflubenzuron. DISCUSSION

This trial measured the fungal efficacy based on rate of population change over time, as opposed to measuring the level of survival at a particular time posttreatment. Also, sampling methods and analyses may be different from those used in other trials. This makes it difficult to establish comparisons with other trials which used fungal pathogens against African grasshoppers. In this trial, B. bassiana treatment resulted in a daily survival rate of 0.9663, which translated to 38.1% control of the grasshopper population after 14 days. Previous work reported by Johnson et al. (1992) and Lobo-Lima et al. (1992), who tested the GHA strain in small plots in Mali and Cape Verde, albeit at somewhat lower dose rates, did not achieve significant control. However, application of B. bassiana in small plots in Cape Verde by Delgado et al., (1997b) resulted in somewhat higher levels of control (45% after 7 days) than those reported here. Application of another hyphomycete entomopathogenic fungus, Metarhizium flavoviride Gams and Rozsypal, developed by IIBC/IITA in Benin for grasshopper control, resulted in a 15-day mortality of approximately 61% (Kooyman et al., 1997). The efficacy differences between B. bassiana trials could result from differing environmental conditions. Sunlight is known to rapidly inactivate B. bassiana conidia (Inglis et al., 1997a), and grasshoppers are known to thermoregulate, raising their body temperatures above ambient level (Chappell and Whitman, 1990), which may enable them to rid themselves of infection by basking in sunlight (Inglis et al., 1997a). The study presented here was conducted in an area predominantly open to sunlight, with sparse tree cover

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DELGADO ET AL.

TABLE 3 Grasshopper Population Changes in Plots Treated with B. bassiana, Diflubenzuron, B. bassiana plus Diflubenzuron, and Fenitrothion, in Mali (Corrected for Survival in Untreated Control Plots) Treatment B. bassiana Diflubenzuron B. bassiana/ diflubenzuron Fenitrothion 0 to 2 days c 2 to 14 days

Intercept (log scale)

Daily survival rate (DSR) e b ⫾ 95%cl a

Goodness of fit (P-value)

% Control 14 days posttreatmentsb

2.22 1.80

0.9663 (0.942–0.991) 0.9754 (0.956–0.995)

0.010 0.014

38.1 29.4

1.86

0.9436 (0.922–0.966)

⬍0.001

55.6

2.01 ⫺1.24

0.2119 (0.013–0.405) 1.1239 (1.055–1.197)

0.016 ⬍0.001

95.5 d 81.8

a

Equals the slope and cl the 95% confidence interval. % control ⫽ 100 (1 ⫺ (DSR)14 ). c Days posttreatment. d Note. % control after 48 h posttreatment. b

to offer shade. The trials of Delgado et al. (1997b) were applied in a moderately forested area which provided significant shade. The higher level of control seen by Kooyman et al. (1997) with M. flavoviride is consistent with the observation that M. flavoviride treatment caused more mortality, compared to B. bassiana, on laboratory-held grasshoppers at hot temperatures, while B. bassiana treatment caused more mortality at cool temperatures (Inglis et al., 1997b). B. bassiana efficacy could potentially be enhanced by making applications in the evening. This would prolong the life of exposed conidia, conceivably leading to germination and cuticle penetration by a greater number of conidia per insect and a higher internal inoculum. This would also allow more time for grasshoppers to become exposed to fungal conidia through feeding on and/or contact with treated vegetation. Delgado et al. (1997b) report that grasshoppers can become infected by exposure to B. bassiana-treated vegetation. Additionally, the inclusion of ultraviolet light protectants in formulations of B. bassiana (Inglis et al., 1995) and in M. flavoviride formulations (Moore et al., 1993) has resulted in enhanced survival or germination of conidia exposed to UV radiation. In the B. bassiana, B. bassiana/Dimilin, and Dimilin treatments, the rate of mortality was slow compared to that of fenitrothion, which achieved over 95.5% control after 48 h. In some cases, slow mortality rates might reduce the utility of entomopathogenic fungi because the target grasshoppers have time to damage crops before they are killed. But it is likely that population density counts by themselves do not measure the full effect of B. bassiana application. Moore et al., (1992) reported that sublethal effects of M. flavoviride infection include reduced feeding, and moribund behavior has often been observed among B. bassiana-treated grasshoppers by this group (unpublished observations). Therefore, sublethal effects such as reduced feeding or fecundity must be considered when judging the overall efficacy of B. bassiana, as must crop yield. In contrast to the fenitrothion treatments, popula-

tions treated with B. bassiana or Dimilin were continuing to decline when monitoring was ceased. It is possible that B. bassiana-treated grasshopper populations may have declined further after 14 days to levels approaching those of the chemical-treated populations. Kooyman et al., (1997) reported that populations of grasshoppers treated with M. flavoviride continued to decline up to 21 days after treatment. This continuous effect, over a relatively long period, may result from secondary cycling of the pathogen through the population (Thomas et al., 1995) or from a slow rate of kill. Subsequent experiments with B. bassiana must be monitored for a longer period of time to determine how long density reductions may continue. Addition of a small amount of Dimilin to the B. bassiana treatment did significantly increase the rate of mortality and so may be useful in B. bassiana-based grasshopper control programs. The mortality rate increase was not as impressive, however, as that seen in a laboratory assay (Reuter et al., 1996). Previous field applications in the United States (Foster et al., 1996) demonstrated that a B. bassiana/Dimilin combination was more effective than other B. bassiana/chemical combinations, but modestly so. Attempts have been made using many other chemical stressors to enhance B. bassiana activity on various insects, with mixed results. For example, imidacloprid was recently found to exhibit strong synergism with B. bassiana (Quintela and McCoy 1997), while Anderson et al. (1989) saw additive effects but no synergism from a variety of insecticides. A synergist which could work at low rates to speed the efficacy of fungal pathogens would be quite useful for grasshopper control because it could help provide faster suppression of populations while still maintaining most of the environmental, health, and political benefits of a pure biological control agent. B. bassiana and B. bassiana/Dimilin combinations, despite their relatively slow rates of kill, may nonetheless offer an effective method of control, especially in an IPM context in which insect populations are attacked before they become economically damaging. The Mon-

ASSESSMENT OF B. bassiana AGAINST GRASSHOPPERS

tana State University Grasshopper/Locust Biocontrol program is presently engaged in a project which aims to treat low-density desert locust recessionary populations in Eritrea and Madagascar with hyphomycete entomopathogens, in an effort to curb the population buildups that lead to swarms. ACKNOWLEDGMENTS This study was undertaken as part of research activities of Montana State University’s Africa Grasshopper/Locust Biocontrol Program. This program was supported, in part, by Grant AOT-0517G-00-4119-00 from the African Emergency Locust/Grasshopper Assistance (AELGA) Project, Africa Bureau, U.S. Agency for International Development, Washington. In addition, it was supported in part by Cooperative Agreement 688-0517-A-00-3387 from USAID/Mali. The authors particularly thank Dr. Allan Showler and Dr. Yene Belayneh, AELGA’s technical advisors, for their advice during various phases of the research project. They also acknowledge the periodic expert advice of Dr. John Henry, Senior Technical Advisor to Montana State University’s Africa Grasshopper/Locust Biocontrol Program. Mr. Tom Kalaris, USDA/ ARS/APHIS, provided valuable advice in statistical analysis. Special thanks to Bernard Maiga, Mariam Diarra, Boureima Cisse, Abdramane Sidibe, Oumar Daffe, Fatimata Ba, Baba Traore, Aboubacar Diombele, and Souleimane Mariko, whose contributions to the success of the field trials were very much appreciated. This is contribution J-5131, Montana Agricultural Experiment Station. REFERENCES Anderson, T. E., Hajek, A. E., Roberts, D. W., Preisler, H. K., and Robertson, J. L. 1989. Colorado Potato Beetle (Coleoptera: Chrysomelidae): Effects of Combinations of Beauveria bassiana with insecticides. J. Econ. Entomol. 82, 83–89. Chappell, M. A., and Whitman, D. W. 1990. Grasshopper thermoregulation. In ‘‘Biology of Grasshoppers’’ (R. Chapman, Ed.), pp.143– 172. Wiley, New York. Connin, R. V., and Kuitert, L. C. 1952. Control of the American grasshopper with organic insecticides in Florida. J. Econ. Entomol. 45, 684–687. Delgado, F. X., Britton, J. H., Lobo-Lima, M. L., Razafindratiana, E., and Swearingen, W. 1997a. Field and laboratory evaluations of leading entomopathogenic fungi isolated from Locusta migratoria capito in Madagascar. In ‘‘Microbial Control of Grasshoppers and Locusts’’ (M. S. Goettel and D. Johnson, Eds.). Memoirs Entomol. Soc. of Canada. 171, 239–251. Delgado, F. X., Lobo-Lima, M. L., Bradley, C., Britton, J. H., and Henry, J. E. 1997b. Laboratory and field studies on the use of Beauveria bassiana (Balsamo) Vuillemin against grasshoppers and locusts in Africa. In ‘‘Microbial Control of Grasshoppers and Locusts’’ (M. S. Goettel and D. Johnson, Eds.). Memoirs Entomol. Soc. of Canada. 171, 323–328. Duranton, J.-F., Launois, M., Launois-Luong, M.-H., and Leqoq, M. 1982. ‘‘Manuel de Prospection Acridienne en Zone Tropicale Seche.’’ Vol. 1, pp. 310–321. Ministe`re des Relations exte´rieures et G.E.R. D.A.T., Paris. Foster, R. N., Reuter, K. C., Black, L., and Britton, J. 1996. Evaluation of the fungus Beauveria bassiana with selected insecticide stressors for control of unconfined rangeland grasshoppers. Arthropod Management Tests 21, 280. Hassan, A. E. M., and Charnley, A. K. 1989. Ultrastructural study of the penetration by Metarhizium anisopliae through Dimilinaffected cuticle of Manduca sexta. J. Invertebr. Pathol. 54, 117–124. Inglis, G. D., Johnson, D. L., and Goettel, M. S. 1997a. Effects of temperature and sunlight on mycosis (Beauveria bassiana) (Hyphomycetes: Sympodulosporae) of grasshoppers under field conditions. Environ. Entomol. 26, 400–409.

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