Monitoring and mating disruption of the maize stalkborer, Busseola fusca, in Kenya with pheromones

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Monitoring and mating disruption of the maize stalkborer, BusseolaJicsca, in Kenya with pheromones B .R . Critchley*§, D.R. Hall*, D.I. Farman*, L.J. McVeigh*, M.A.O.A. Mulaa+ and P. Kalama* *Natural Resources Institute, Central Avenue, Chatham Maritime ME4 4TB, UK; +Kenya Agricultural Research Institute, Nairobi, Kenya and *National Agricultural Research Centre, Kitale, Kenya

studies in the Tram-Nzoia District of Kenya established that several locally made water traps were as effective as commercially available plastic funnel traps for trapping male moths of Busseolu fusca (Fuller) with pheromone. The effects of trap colour, trap spacing, trap height and the type of pheromone dispenser and loading on catches were also investigated. A slow-release pheromone formulation, developed at the Natural Resources Institute (NRI) and commercialised by AgriSense, gave high levels of communication disruption when applied at 40 g a.i. ha-’ as 250 or 500 point sources ha-‘. This was observed to persist for at least 18 weeks and was predicted to last for 6 months from release rate studies. In trials on 1.0 and 0.5 ha plots some reduction in damage levels was observed in treated plots, leading to the conclusion that mating disruption had occurred, but further studies are required to optimise the timing and scale of application. 0 1997 Elsevier Science Trapping

Ltd Keywords: Busseola fusca; pheromone; trap; mating disruption; maize: Kenya

Introduction

Maize is a major food crop in most parts of Africa south of the Sahara. In Kenya, about 80% of the population relies on maize as a staple diet and approximately 1 x lo6 ha are grown annually giving a total annual production of (2-3) x 10” t (Anonymous, 1990). Yields in farmers’ fields can vary considerably, from 800 kg ha-’ to ten times that amount, according to length of the growing season, cultural practices and pest management strategies deployed. Around Kitale, where the growing season is long and rainfall abundant, an average yield of 5.6 t ha-’ is obtained, although yields up to 8.5 t ha-’ are possible in good farmers’ fields and 13.9 t hap’ on experimental plots (Acland, 1971). Production is affected by maize genotype, time of planting, plant density, weed control, fertiliser and pest control (Allan, 1971). Of the pests which attack maize, stalkborers are the most important (Farrell et al., 1995). Their incidence and distribution in both maize and sorghum have been well documented in Kenya (Ogwaro, 1983; Seshu Reddy, 1983; Walker, 1967), with Busseolu fusca (Fuller) (Lepidoptera: Noctuidae) being the dominant species in highaltitude areas (Mulaa et al., 1992) such as the TransNzoia district, which is responsible for over 60% of &To whom correspondence

should he addressed.

production in Kenya. Reduction in grain yield results from the tunnelling activities of B. fisca larvae in the main stem, which interferes with the supply of nutrients to the plant, resulting in either death of the plant - known as ‘dead heart’ - or a weakening and breakage of the stem (lodging). Maturing cobs may also be attacked and this will predispose them to fungal rots. In East Africa, losses in maize because of stalkborer have been reported to vary between 20 and 50% (Walker, 1967) with 1.2% loss per 1% attacked in Kitale (Walker, 1983). Other studies, for example, that by Ogwaro (1983), have reported correlations of numbers of stalkborer larvae with damage and yield loss. Because stalkborer larvae are protected within the stem, they are not easily controlled by insecticides and best results are obtained against first instar larvae which have just hatched from eggs laid under the leaf sheaths and before they bore into the stem. Insecticides were shown to be effective against another stalkborer species, Chilo parteflus Swinhoe (Lepidoptera: Pyralidae), when properly used with repeated applications, but their use is not always economically feasible for small-scale farmers (Warui and Kuria, 1983). Various non-chemical means for control of stalkborers are being investigated (Farrell et al., 1995), including adjusting planting time, intercropping (e.g. with cowpea), host plant resistance and release of exotic parasites.

Crop Protection 1997 Volume 16 Number 6 541

Busseola fusca and pheromones: B.R. Critchley et al.

The female sex pheromone of B. fusca was identified by Hall ef al. (1981) and a synthetic blend was found to be highly attractive to male moths in Malawi, Zimbabwe and Kenya (Beevor et al., 1983). Revington et al. (1984) reported good correlations between catches of B. fusca moths in sticky delta pheromone traps and catches in light traps in South Africa, and Hoechst, Frankfurt, Germany took up commercial production of these traps for monitoring B. fisca under the Biotrap trademark. Revington whereby (1987) proposed an action threshold chemical control of B. fuscu larval populations is initiated when the average weekly catch of adult moths in three delta traps per site exceeds two moths. Subsequently, Hoechst and International Pheromone Systems (IPS) Ltd, Ellesmere Port, UK introduced more sophisticated dry plastic funnel traps, Omnitrap and Unitrap, respectively. These were evaluated in South Africa by Van Rensburg (1992), and Medvecky et al. (1992) compared water traps and net traps in Kenya. Pheromone traps are used for monitoring a wide range of other insect pests (Wall, 1989), and have the advantages of being simple and cheap to construct and operate and specific for the target pest. Synthetic sex pheromones are also used for control of insect pests by mating disruption (e.g. Campion et al., 1989; Hall, 1995). A slow-release formulation for pheromones was developed at the Natural Resources Institute (NRI) and commercialised by the UK company AgriSense-BCS, Pontypridd, Mid Glamorgan, Wales. This formulation has been used successfully against cotton bollworms Pectinophoru gossypiellu (Saunders) (Lepidoptera: Gelechiidae) and Eurius spp. (Lepidoptera: Noctuidae) (Chamberlain et al., 1993; Hall et al., 1994) and rice stemborers Chilo suppressulis Wlk. (Lepidoptera: Pyralidae) (Casagrande, 1993) and Scirpophugu incertulus Wlk. (Lepidoptera: Pyralidae) (Cork and Basu, 1996; Cork et al., 1996; Hall et al., 1994). Mating disruption uses non-toxic chemicals that are specific for the target pest and without effect on non-target organisms, including beneficial predators and parasites. This approach is thus highly suitable as part of an integrated pest management strategy for food crops. This paper describes studies of different pheromone trap and lure parameters for monitoring B. fiscu, and initial investigations on the effects of mating disruption of this pest with pheromone in Kenya. Materials and methods Monitoring

of B. fusca adults

Monitoring studies were conducted at the National Agricultural Research Centre (NARC), Kitale, between September 1993 and December 1994, and evaluated trap design, trap colour, trap spacing, trap height, and pheromone dispensers and concentrations. Pheromone

lures. Unless otherwise stated, traps were baited with a standard lure for B. &scu consisting of a polyethylene vial (23 mm x 9 mm x 1.5 mm thick, Just Plastics, London, UK) impregnated with 1 mg of a 10:2:2 blend of (Z)-11-tetradecenyl acetate

542

Crop Protection 1997 Volume 16 Number 6

(Zll-14:Ac), (E)-11-tetradecenyl acetate (Eli-14:Ac) and (Z)-9-tetradecenyl acetate (Z9-14:Ac) with an equal amount of 2,6-di-tert-butyl-4-methylphenol prepared at NRI (Hall et al., 1981). Trap design. Eight different types of trap of three basic designs - water, sticky delta and funnel were evaluated. Six of the traps were locally made and two were imported with the objective of selecting the most efficient, cheap and easy to operate trap under Kenyan conditions. Designs tested were: (1) four water traps, three based on locally made plastic containers of Karanga (yellow), Cowboy (orange) and Kimbo (white) cooking fat of 500 ml capacity and the fourth on a 5 1 metal paint tin (bare metal); the holes containers had three square plastic (5 cm x 5 cm) cut just below the lid and the metal paint tin had four round holes (of 5 cm diameter) cut 5 cm from the lid; the traps tiere filled with water containing a little detergent to a level just below the holes; (2) two sticky delta traps, one imported (AgriSense, UK) made of white plastic (20 cm x 18 cm x 11 cm high) and the other of similar design made locally from iron sheet; (3) two funnel traps, one imported (AgriSense, UK) consisting of a funnel I (15 cm outside green moulded plastic diameter) and green collecting box with a roof 3 cm above the funnel rim, and the other of similar design made locally of sheet metal. Traps were suspended on poles 1.5 m above ground and 50 m apart in a randomised block design. Trap

colour. Four colour combinations (funnel +bottom) of plastic funnel traps (AgriSense) were tested: green+green, yellow+green, yellow+white, and green+white. Trap spacing. Catches in three all-green, plastic funnel traps placed parallel to the general wind direction and separated by 30 m, 60 m or 90 m were compared with catches in a single isolated trap. Trap height. Catches of male B. fuscu moths in all-green plastic funnel traps at 0.5 m, 1 m, 1.5 m and 2 m above ground were compared. The maize was approximately 2 m high (6 weeks). Comparisons of pheromone dispensers and loadings. In 1993 and 1994, catches were compared in all-green

plastic funnel traps baited with polyethylene vials impregnated with 2 mg, 1 mg, 0.5 mg or 0.1 mg of the pheromone blend or with white rubber septa (Aldrich, Milwaukee, WI, USA; Catalogue Number Z10,072-2) impregnated with 5 mg or 1 mg of pheromone. In 1995, the standard lures were compared with similar, commercially available lures in yellow and white plastic funnel Unitraps of identical design but manufactured by IPS Ltd. The standard lures were also compared with Long-Life lures containing 10 mg of pheromone a.i. (IPS Ltd) in the yellow and white Unitraps. The standard lures were renewed every 4 weeks and the Long-Life lures were not renewed.

Busseola fusca and pheromones: B.R. Critchley et al. Data unalysis. Trap catches

were recorded each day and lures were renewed every 4 weeks where necessary. Catches were transformed to x’ = (x+0.5), subjected to analysis of variance, and differences between means tested for significance by Duncan’s Multiple Range Test (DMRT). Mating disruption of B. fusca

Small block field trials. Preliminary

trials were set up at the NARC field station at Kitale during the 1993 maize cropping season. The PVC slow-release formulation, developed at NRI and commercialised by AgriSense as Selibate, was used and supplied as a string 3 mm in diameter containing 5% of the B. fusca pheromone. The formulation was cut into pieces of different lengths to give four treatments: 40 g a.i. ha- ’ at 1000 point sources (p.s.) per hectare (10 cm pieces), 40 g a.i. ha- ’ at 500 p.s. ha-’ (20 cm pieces), 40 g a.i. ha- ’ at 250 p.s. ha-’ (40 cm pieces) and 20 g a.i. ha-’ at 500 p.s. ha-’ (10 cm pieces). Two replicates of the first two treatments were compared on 0.2 ha plots and two replicates of the last two treatments on 0.1 ha plots. The effects were assessed by comparing catches of B. fuscu in all-green plastic funnel traps (AgriSense) baited with the standard lure within treated areas with catches in nearby untreated plots of similar magnitude. The treatments were located in an 8 ha field of maize and were separated from each other by at least 25 m in a randomised layout. The percentage level of communication disruption (% CD), was calculated according to the following equation: [(mean trap catch in untreated maize -mean trap catch in treated maize) x 1001 %CD =mean trap catch in untreated

maize

Release rate determination. To determine

release rates of pheromone from the formulation under field conditions, 10 cm lengths of formulation were attached to a row of maize plants adjacent to the experimental areas. Samples were removed at weekly intervals and returned to NRI for analysis. A similar experiment was run in a wind tunnel at NRI maintained at 27°C and 8 km hh’ wind speed. For analysis, two 2 cm lengths were cut from the centre of each sample and weighed accurately, and the pheromone was extracted overnight in hexane (2 ml) containing 2 mg of hexadecyl acetate as internal standard. The extracts were analysed by gas chromatography (GC) with flame ionisation detection using a glass column (1.8 mm x 2 mm i.d.) packed with 1.5% Carbowax 20M on Chromosorb G, temperature programmed from 120°C to 220°C at 4°C min- I. Total tetradecenyl acetate isomers was quantified against the internal standard. The isomeric composition of representative samples was determined by GC using a fused silica capillary column (25 m x 0.32 mm i.d.) coated with CP Wax 52CB (Chrompack, Middelburg, Netherlands), with oven temperature held at 70°C for 2 min then programmed at 20°C min ’ to 120°C and then at 4°C min’ to 220°C.

Large and medium block field trials. Larger-scale

field trials were carried out at the NARC station, Kitale (l”N, 35”E; 1890 m above sea-level (ASL)), and the Agricultural Development Corporation (ADC) farm at Ol’ngatongo Complex, near Kitale (1925 m ASL), in the Trans-Nzoia district of Kenya during the 1995 maize cropping season. Maize (commercial hybrid 614D at NARC and 614 at ADC) was planted with 30 cm spacing and 75 cm between rows between 10 and 26 April 1995. The pheromone formulation was similar to that used in 1993 except that the pheromone loading was 8% to make it more cost-effective. Previous work at NRI showed there was no difference in the release rate expressed as a percentage of the initial loading for the 5% and 8% formulations. The formulation was applied by hand at 40 g a.i. hap’ at two of the rates found to be effective previously: 500 p.s. ha - ’ (15 cm pieces) and 250 p.s. ha ~ ’ (30 cm pieces). The two treatments and untreated control were on adjacent bIocks with the control upwind, and replicates were separated by at least 100 m. Three replicates on 1 ha plots at the NARC farm and two replicates on 0.5 ha plots at the ADC farm were set up at the end of May 1995 and monitored for 18 weeks. Communication disruption levels were calculated as above, using data from three funnel traps placed equidistant along the diagonal in 1.0 ha plots and two traps similarly positioned in 0.5 ha plots. Damage

and yield assessments. Plant damage and yield assessments were made for all plants in 10 m x 10 m sub-blocks at the centre of each block. Measurements or estimates were obtained for (1) plant population; (2) percent plants lodged; (3) percent stalks and cobs damaged by B. fisca larvae; (4) numbers of B. fusca larvae and pupae in 100 plants selected at random; (5) percent damage by insects other than B. fusca; (6) percent damage by fungal pathogens; (7) percent damage by vertebrate pests (mainly birds and rats); (8) field weight of healthy cobs from the 100 plants in (4). Damage was rated on a scale of one (low) to five (high) for each cob on the 100 plants selected in (4), and the mean cob score was determined. This was used to obtain an estimate of the percentage yield loss according to Bosque-Perez and Mareck (1991).

Results Monitoring

of 6. fusca adults

Trap design. Catches of male B. fusca moths in the locally made water traps were not significantly different (PcO.05) from those in the commercially available AgriSense funnel traps, although catches in the locally made metal delta and funnel traps were significantly lower (Table 2). Trap colour. Highest catches were recorded in the green+green and yellow+green traps, and the lowest in the yellow+white traps (Table 2). Trap spacing. The lowest mean catch was observed at the 30 m spacing, and catches at the other spacings

Crop Protection 1997 Volume 16 Number 6

543

Busseola fusca and pheromones: B.R. Critchley et al. Table 1. Catches of B. fusca moths in different trap designs

(four

replicates)

Mating disruption Small

Detransformed mean catch per night per 4 traps” Trap design

1993 (20 nights)

1994 (43 nights)

3.la 2.2b 1.2c 0.7cd 2.3b 0.6d

1.5a 1.2b l.Ob 0.3d 0.9b 0.7c l.Ib ObC

Water trap (Cowboy) Water trap (Kimbo) Water trap (Karanga) Water trap (paint tin) Delta trap (AgriSense) Delta trap (metal) Funnel trap (AgriSense) Funnel trap (metal)

block

of El. fusca

field

complete suppression moths was maintained 41 nights (Table 6). untreated areas were detect any differences treatments.

trials.

In these trials, almost of trap catches of B. fusca male in the treated areas for at least However, trap catches in the low, and it was not possible to in the effects of the different

(Table 4).

release rate. Analysis of the pheromone remaining in the formulation exposed in the field showed that after 71 days 67% of the pheromone remained (Figure I). Shade temperature during this period ranged from a maximum of 28°C to a minimum of 9.1”C. When the formulation was exposed at a constant 27°C in the laboratory wind tunnel, 24% of the initial loa,ding of pheromone remained after 73 days (Figure I). There were no significant differences in release rates of the three pheromone components. Release of pheromone was exponential in both cases (Figure I) and the results indicated that, under the field conditions observed, 37% of the initial loading of pheromone would remain after 6 months, the maximum period that would be required to protect the crop in the field.

Pheromone

Large and medium block field trials. In the 1 ha trials

z’Valuesin different

the same column

at P = 0.05 (DMRT),

followed

hy the same

data transformed

letter

x’ =

are

not

Pheromone

significantly

(x+0.5).

and in the isolated traps were similar. In all cases, catches were highest in the upwind traps and were progressively lower in the central and downwind traps (Table 3). Trap height. Traps at 1.5 m, i.e. 0.5 m below crop height, caught more moths than did traps at other heights, and traps at 0.5 m had the lowest catches

dispensers and loadings. The highest trap catches were recorded by traps with polyethylene vials containing 2 mg of the pheromone, and catches declined progressively as the loading was reduced. Catches with the septa were lower than with the vials, even with the 5.0 mg loading (Table 5). Funnel traps baited with Long-Life lures containing 10 mg of pheromone a.i. trapped significantly more moths (PcO.05) than did identical traps baited with standard lures renewed every 4 weeks over an 18 week period. Mean catches per night totalled over the three replicates were 1.9 and 0.5, respectively. The Long-Life lures were still active after 6 months, when the experiment was terminated. Table 2. Catches

of 6. fusca moths in traps of different colours

(four replicates) Detransformed mean catch per night per 4 traps”

Trap colours

Funnel

Base

1993 (6 nights)

1994 (8 nights)

green

green

1.7a

yellow green yellow

green white white

1.5a l.la 0.4b

I .3ab 1.5a l.lb 1.Ob

“Values in different

the same column

at P = 0.05 (DMRT),

followed

by the same

data transformedx’

letter =

Discussion Monitoring

are nor significantly

(x+0.5).

-Table 3. Catches of 13. fusca moths at different trap spacings

both treatments gave 100% communication disruption for up to 7 weeks (Figure 2). After the seventh week, trap catch suppression in excess of 80% was observed for the next 11 weeks. Of the two treatthe larger dispensers distributed at ments, 250 p.s. ha-’ appeared to give a slightly better degree of disruption than the smaller dispensers distributed at 500 p.s. ha-‘. Similar results were obtained in the 0.5 ha trials (Figure 3), with both treatments giving mean communication disruption levels of 95% over 17 weeks. The pheromone treatments were applied too late to prevent mating of moths emerging from overwintering larvae, which resulted in some early season damage. However, the presence and effects of B. fuscu were generally lower in the pheromonetreated plots compared with the untreated plots, and cob damage and estimated yield loss were significantly lower in the treated plots (Table 7).

of B. fusca adults

Locally made water traps caught similar numbers of available plastic funnel traps and more than the commercial sticky

B. fusca moths to the commercially

(three replicates) Detransformed

mean catch per night per 3 traps + SD

Spacing

Downwind

Central

Upwind

30 m

1.72* 1.12 2.03 + 1.09 2.25 k 1.03

2.02? 1.11 2.19k1.01 2.34 k 0.83

2.47 + 1.29 2.42 + I .OO 2.45 & 0.90

60 m 90 m Single trap “Values followed by the

544

Overall mean:’ 2.07b 2.22ab

2.34~ 2.2lab

same letter

arc not significantly

different

Crop Protection 1997 Volume 16 Number

at P =

6

0.05

(DMRT),

data transformed

x’ =

(x+&S).

Busseola fusca and pheromones: Table 4. Catches of B. fusca at different trap heights in maize 2 m tall (four replicates) Detransformed mean catch per night per 3 traps” Trap height (m)

1993

1994

0.5

0.8c I .6h 2.3a l.3b

2.3d 3.7b 4.2a 3.2~

I .o 1.5 2.0

“Values in the same column followed hy the same letter are not significantly different at P = 0.05 (DMRT), data transformed A-’ = (x+0.5).

delta traps or locally made metal delta or funnel traps. These locally made traps are extremely cheap, as the containers have no residual value and the labour for cutting holes in the sides is almost negligible. Since the above trials were conducted, the addition of soap to the water was found to enhance trap catches, with perfumed soap of the Imperial Leather brand giving the best results (Mulaa, personal communication). Further trials are needed to assess what effects, if any, the perfume element has in eliciting moth attractancy. Van Rensburg (1992) similarly found that funnel traps were superior to delta traps both in terms of numbers caught and estimation of moth populations. Medvecky et al. (1992) found that net traps (Hartstack et al,, 1979) caught more B. fusca moths than white water traps but were complicated to assemble and maintain. The colour of the funnel trap had some effect on catches, with traps having white bases tending to catch fewer moths than those with yellow bases. However, trap colour may not be an important factor Table 5. Catches of f?. fusca moths in funnel traps baited different pheromone dispensers and loadings (four replicates)

with

Detransformed mean catch per night per 4 traps” Loading Dispenser Polyethylene vial Polyethylene vial Polyethylene vial Polyethylene vial Rubber septum Rubber septum Control (no hire)

(mg)

1993 (7 nights)

1994 (14 nights)

2.0 1.0 0.5 0.1 5.0 1.0 _

1.8a 1.4b 0.4cd O.lde 0.7c 0.3de O.Oe

1.5a 1.4a 0.8b 0.3c 0.6bc 0.3c O.Od

Table 6. Communication

disruption

of B.

in influencing trap catches of nocturnally active insects, as was demonstrated by Krishnananda and Satyanarayana (1989) when monitoring the noctuid moth Spodoptera &m-a F. in India. Traps should be placed just below the crop canopy for maximum catches, and at 60 m or greater spacing between traps. At 30 m spacing along the windline catches were reduced, presumably as a result of interference of the pheromone plumes. In this experiment, catches in the upwind traps were higher than those in traps downwind at all spacings, although the differences were significant (P~0.05) only at the closest (30 m) spacing. This effect has been observed by others (Bradshaw et al. (1989) and references therein), who proposed it is the result of the downwind traps ‘recruiting’ moths which overshoot to transfer to the upwind traps. The type of pheromone dispenser and the pheromone loading had significant effects on catches. Rubber septa performed poorly compared with increased with polyethylene vials, and catches increased pheromone loading, as found previously by Hall et al. (1981). The difference in catches with 1 mg and 2 mg loadings was small, but increasing the loading to 10 mg, as in the commercial Long-Life lure, increased catches and longevity of the lure, which remained effective for at least 18 weeks under field conditions. Medvecky et al. (1992) only evaluated rubber septa dispensers, and Revington (1987) and Van Rensburg (1992) used commercial polyethylene dispensers of undisclosed composition, but both experienced similar increases in moth catches with increased pheromone loading. The results of the trapping experiments were used by Mulaa (1995) to develop a monitoring system for B. fisca consisting of three water or plastic funnel traps baited with a polythene vial containing 1 mg of pheromone at 1.5 m height and 60 m apart. Trapping data taken over 5 years showed that three generations of B. fusca occurred each year, and indicated a mean weekly catch of eight moths per trap as a likely economic threshold for pesticide application, which was later confirmed in subsequent field trials (unpublished data). Mating disruption

~‘Values in the Same column followed by the same letter are not significantly different at P = 0.05 (DMRT), data transformed x’ = (x+0.5).

B.R. Critchley et al.

of B.

fusca

The timing of applications of the mating disruption trials was unfortunate in that they coincided with a decline in population numbers following emergence of adults from overwinterig larvae. This was due to poor or inadequate pest monitoring before the

fusca in small plot trials, September-November

1993

Mean catch per trap per night (2 replicates) 0.1 ha (34 nights)

0.2 ha (41 nights) sources ha- I: a.i. g ha- I:

1000 40

500 40

0 control

250 40

500 20

0 control

Before application After application % disruption

3.42 0.012 99

2.92 0.0 100

5.92 0.98

1.67 0.015 98

3.67 0.015 98

2.0 0.75

Crop Protection 1997 Volume 16 Number 6

545

Busseola fusca and pheromones: B.R. Critchley et al.

of the treatments. However, the trials showed that a slow-release formulation of the B. jma pheromone gave high levels of communication disruption for at least 18 weeks, and release rate studies indicated that this formulation should be effective for up to 6 months. Trials in the 0.5 ha and 1.0 ha plots using 40 g a.i. ha-’ as either 250 or 500 p.s. ha- ’ gave some indication of reductions in stalkborer damage and yield loss in the plots treated with pheromone relative to untreated plots, but further work is required to investigate the effects of timing of application and plot size on the control achieved. In a survey carried out by Mulaa (1995) in the Trans-Nzoia district, 58% of farmers applied insecticide, and most of these (96%) did so only once in the season. Average spending on insecticide and application was 521 Ksh ha-’ (approximately $12) representing 5% of all production costs. Farmers’ perceptions of the benefits from this varied widely, with an average increase of 12 bags (90 kg each) per hectare, representing 10,800 Ksh or 25% of the total yield. At present, mating disruption at more than $50 ha-’ would not be cost-competitive with hand application of the cheaper insecticides by small farmers. On larger farms, increasing labour costs and the need for high levels of supervision for hand application of dusts and granules has led to use of pyrethroid formulations applied by tractor-mounted sprayers. These are generally perceived to be less effective than hand-applied granules, and the tractors can only be used early in the season when the plants are small. In the first instance, pheromones may be more applicable on these larger farms, providing the possibility for season-long control with a single, early application of the pheromone formulation. The general principles of mating disruption established here should also be applicable to other cereal stalkborers for which pheromones have been identified, e.g. Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae) (Nesbitt et al., 1979). commencement

100

@ :E

60

2 g

8 40

20

O),,~,,,.,,,,,,,,,,,,l 0

20

40

60

80

100

120

140

160

180 200

time (days)

Figure 1. Release rates of pheromone from PVC formulation in field and laboratory

-

6

+ -t--A

500 ps/ha 250 ps/ha untreated

0

10

5

15

20

weeks Figure 2. Trap catches in 1.Oha trials at NARC, Kitale (arrow indicates application of pheromone formulation, 26-29 May 1995)

+ El -t-

-I

0

2

500psiha 250 ps/ha untreated

4

+

A :

A: 1

A’:.

6

8

10

12

14

16

18

20

weeks Figure 3. Trap catches in 0.5 ha trials at ADC Farm, Ol’ngatongo Complex (arrow indicates application of pheromone formulation, 31 May 1995)

546

Crop Protection

1997 Volume 16 Number 6

Acknowledgements This publication is an output from a research project funded by the UK Department for International Development (formerly Overseas Development Administration), which can accept no responsibility for any information provided or views expressed. The work was funded from ODA Project R5285 within the Crop Protection Programme in collaboration with the KARI-ODA Crop Protection Project in Kenya. We are grateful to Gilbert N. Kibata, John Sutherland and Graham Farrell for their full support of this project, R. Butaki, Director, NARC, Kitale, for permission to conduct the large block trials at the NARC farm, James Kahuro, Technical Manager, ADC, Kitale, for permission to conduct the medium block trials at the Ol’ngatongo Complex near Kitale, Richard Muhomah, Estates Director, Kirit Patek Research and Development Director, and Richard Ruto, Estates Manager, of EATEC for permission to conduct medium block trials at the Chemoset Estate, Soy. We also thank John Sherington (NRI) for help

Busseola fusca and pheromones: B.R. Critchley et al. Table 7. Effects of treatments on variables relating to plant damage Treatment” 500

Variable ?+ stalks damaged by B. @scu % cobs damaged by B. fusco No. B. fusca larvae per 100 plants No. R. fusca pupae per 100 plants % other insect damage 9%fungal damage % vertebrate damage Mean cob score o/oEstimated yield loss 5ED. standard error of diffcrcncc: approximately 2 SED.

p.s. ha- ’

250 p.s. ha- ’

22.00a 8.30a 9.00a 0.67a 0.47a 4.9sa 2.08a

10.80a 0.67a 0.3Oa 4.83a 4.OOa I .04a s.93a

1.04a hv , the same lcttcr

with statistical analyses, and AgriSense-BCS provision of the Selibate formulation.

24SOa 12.40a 16.20a 0.33a 0.17a 4.0Oa 4.08a 1.10b 7.17b

19.5&l lhoa

5.95a means followed

Untreated

in each row are not significantly

for

different

SED 4.30 2.70 3.20 0.48 0.40 I .43 1.26 0.02 0.49

hased on a ‘least significant difference‘

of

Pyralidae) by mating disruption on rice in India: effect of unnatural pheromone blends and application time on efficacy. Bull. Entomol. Rex 86, 515-524

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Received I6 January 1997 Accepted 17 March 1997

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