Medical and Veterinary Entomology (1996) 10,97-100

S H 0 RT C 0 M M U N IC ATION

Autosterilization of the house fly, Musca domestica, using the chitin synthesis inhibitor triflumuron on sugar-baited targets

J U L I A H 0 WARD and R I C H A R D WA L L School of Biological Sciences, University of Bristol

Key words. House fly, Musca dornestica, autosterilization, control, triflumuron, sucrose-baited targets.

In livestock husbandry systems the house fly, Musca domestica Linnaeus (Diptera: Muscidae), can be a common problem, af- fecting animal performance and transmitting disease (Drummond et al., 1988; Axtell &Arends, 1990). House fly control is usually attempted through the application of a wide range of chemical insecticides. However, complete reliance on conventional insec- ticides brings a variety of associated problems. These include the development of resistance by the target species (Chapman et al., 1993), direct and indirect effects on non-target organisms and the presence of insecticides in the food chain (Lancaster & Simco, 1969). As a result, there is a growing need to either re- place or, at the very least, supplement the use of insecticides with a range of alternative, non-insecticidal, control techniques.

A number of non-insecticidal control techniques for house fly control have been explored previously, including mechanical removal of the livestock dung in which the files breed (Peck & Anderson, 1970), the release of parasitic hymenoptera (Morgan et al., 1981), sterile male release (Drummond et al., 1988) and integrated pest management (Axtell, 1970). An alternative control technique which has been considered for housefly control is autosterilization. Autosterilizing devices attract wild flies in the field and either sterilize them directly, usually using chemosterilants, or produce a similar end result by transovarial effects on eggs, larvae or pupae. To maximize its effectiveness the autosterilizing system used should affect both sexes of the target species (Langley & Weidhaas, 1986; Wall & Howard, 1984). The development of autosterilizing devices for housefly control was first considered in the 1960’s (LaBrecque et al., 1962; LaBrecque & Meifert, 1966). However, this work met with limited success, primarily because of the non-availability at that time of sterilants which were both effective against target flies yet safe for nontarget organisms.

The insect growth regulators (IGRs) have been shown to hold

Correspondence: Ms J. J . Howard, School of Biological Sciences, The University of Bristol, Woodland Road, Bristol BS8 lUG, U.K.

considerable promise as potential control agents (Hammann & Sirrenberg, 1981). In particular, the chitin synthesis inhibitor, triflumuron, was found to be effective in preventing egg hatch and larval development in the house fly when applied topically and tarsally to female M.domestica (Knapp & Herald, 1983; Knapp & Cilek, 1988; Howard & Wall, 1995a). In addition, after male house flies were forced into tarsal contact with surfaces treated with triflumuron, subsequent mating with unexposed vir- gin females resulted in inhibition of egg hatch (Howard & Wall, 1995b). However, IGRs such as triflumuron have not been used previously for autosterilization, largely because of the practical difficulty of inducing flies to pick up an effective transovarial dose. For example, the production of significant egg hatch inhi- bition following tarsal contact with treated surfaces by female or male adult M.domestica was shown to require contact with 20% triflumuron suspension concentrate for at least 1 h (Howard & Wall, 1995a, b). Such concentrations and contact times are not realistic for a practical control device. Recent studies, however, have suggested that it may be possible to induce both male and female house flies to pick-up an effective ovicidal and larvicidal dose by presenting triflumuron on sugar-baited targets (Wall & Howard, 1995b).

To examine the efficacy of triflumuron-treated sugar-baited targets for autosterilization, laboratory trials were carried out us- ing M.domestica (Coopers susceptible strain) obtained from the Central Science Laboratory, Slough, U.K. Adults were separated according to sex, within 2 h of emergence over a 12 h period. This was continued until 150 flies of each sex had been col- lected. Flies were divided into four identical 30 x 30 x 30 cm cages so that seventy-five flies of a single sex were placed in each cage. Each cage was supplied with a water fountain and an egg/milk powder protein source. A single sugar-baited. white. polyester target (5 x 15 cm), which had been dipped in 3% triflumuron suspension concentrate (previously shown to be equivalent to 0.328 mg of a.i./cm’; Howard &Wall, 199%). was suspended from the roof of one of the cages containing males

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only and one ofthe cagex containing females only. Identical sugar- baited targets. which had not been treated with tritlumuron. were suspended from the roof of each of the two remaining cages. Targets were left in their respective cages for 24 h.

Following exposure. batche5 of twenty-five flies were trans- ferrcd to a further four 15 x IS x 15 cm cages in the following comhin;ition.\: ( I ) tu enty-five triflumuron-exposed females with tKenty-fiLe trifluniuron-exposed males. (2) twenty-five ex- pwed ternale5 wi th twenty-five unexposed males. (3) twenty- fi \e unexpo\ed females with twenty-five exposed males. and (4) tu,enty-fi\e unexposed females with twenty-five unexposed male\ the control). All cages were supplied with granulated

. a water fountain. and an egg/powder mixture. and were held at a constant 25°C under a 16:s h L:D cycle.

Ti\we paper soaked in milk was provided for oviposition 72 h after vdult emergence. This was replaced every 24 hand inspected for the dppearance of eggs. Eggs were collected from the tissue and tran\ferred tci a damp filter paper with approximately 2 g o t ' l a r ~ a l medium. Larval medium consisted of mashed rat food pellets ! Beekay Feeds. Rat and Mouse Standard DietR. B & K L'niversal ) (Howard & Wall, 1955a). The filter paper was placed in a covered petri dish and stored in an incubator at a constant 7 5 'C and a I6:X L:D cycle. The number of hatched and unhatched eggs were counted 24 h after collection. using a 6fereoniicrOscope. Eggs were collected from all cages for 18 d a y tollowing exposure to the targets. To assess the effect on the F , generation. any surviving larvae from the first egg batch and each batch collected every 3 days thereafter were followed through to adult emergence. The entire procedure was replicated three time\.

All percentages were subjected to angular arc-sin transforma- tion prior to analy\is of variance and Tukey multiple range tests IStatpxphic\'. Manugistics). in which the variables of sex treated and da! \ after treatment uere treated as factors. Detransformed means tSE arc presented in the text throughout.

The percentage egg hatch. recorded over the 18 days of c g ~ ~ ~ o l l w t i ~ i i i , was dependent on the sex exposed to the

tritlumuron- treated targets (F = 29.5, P < 0.001). Furthermore, each treatment was significantly different from all other treatments ( P < 0.05). Exposure of males alone to triflumuron resulted in 69 t 3% egg hatch, whereas after exposure of females alone, 58 k 5.4% of eggs hatched. After both sexes had been exposed to the triflumuron- treated targets 45 -c 5% of eggs hatched. In contrast, in the control cages where neither sex had been exposed to triflumuron 91 f 0.8% of eggs hatched.

For larvae which were able to eclose from the egg, pupariation occurred in all treatments. There was no significant difference in percentage pupariation between treatments 1,2 or 3, which ranged between 23 k 7.9% and 28 -c 5.1% (F = 0.04, P = 0.99). How- ever, the percentage pupariation was significantly lower in these three treatments than in the controls, where 59 k 4.9% of larvae pupariated (F = 5.69, P < 0.001). The mean adult emergence in treatments 1-3 was 95 k 1.2%, and was not significantly differ- ent from the mean percentage adult emergence for the controls. which was 96 f 0.9%.

Examination of the change in percentage egg hatch with time following initial exposure to the triflumuron-treated targets, shows that egg hatch inhibition decreased significantly with time for treatments 1-3 (F = 12.99, P < 0.001. For example, in treatment I , where both sexes were exposed to triflumuron, mean percent- age egg hatch remained below 4% for 5 days following expo- sure, before climbing towards control levels, 16 days following exposure (Table I ) . In contrast, no consistent change in percent- age egg hatch with time was observed in the control, which re- mained constant at approximately 90% (Table 1). Similarly, for larvae that eclosed. the percentage that reached pupariation also increased over time in treatments 1-3 (F = 7.62, P < 0.001), whilst again showing no consistent change over time in the control, where pupariation remained at approximately 60% (Table I ) . Adult emergence remained consistently high at ap- proximately 95% for all treatments including the control.

Autosterilization overcomes many of the problems associated with the need to mass rear and release sterile or genetically modi- fied flies. Furthermore, when compared to conventional killing

Table 1. The detrandomed mean arc-sin percentage egg hatch and detransformed mean arc-sin percent- age pupariation ( cSE) i n 5-day periods following 24 h exposure of adult house flies, M K X U domestica, to wcro\e-baited target5 dosed with 3% tritlumuron suspension concentrate. In treatment 1 both sexes were e x p o m i to the triflumuron treated targets; in treatment 2 only females were exposed: in treatment 3 only male\ were expo5ed: i n the control (treatment 4) neither sex were exposed to triflumuron.

Detransformed mean arc-\in percentage (eSE) lh ! s

d t e r Treatment I Treatment 2 Treatment 3 Control twpwure (both sexes) (females only) (males only)

Egg h u h s .s 3.4 (22.8) 7.8 (c4.6) 42.5 (210.3) 9 I .9 (22.4) 6.- 10 -12.0 ( d . 3 ) 53.8 (28.1) 65.8 (24.6) 91.2 (21.5) 11-15 62.9 (c4.8) 77.7 (22.8) 74.0 (23.4) 92.6 (21.3) I6 76.8 (c3.6) 83.5 (22 .1) 80.2 (c5.3) 88.2 (c1.5)

-;r 7 2.7 ( t5 .6) 5.1 (27.5) 14.9 (c7.8) 55.8 (c5.2) 8- I 1 35.4 (t21.7) 23.8 (22.8) 32.9 (c3.3) 79.4 (c6.7) 12- 15 41.6 (clo.9) 41.7 (cl2.9) 26.5 (214.8) 60.6 (c11.9) I 6 38.6 (213.6) 43.4 (210.4) 42.9 (27.8) 48.6 ( d . 8 )

Pupariation

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Autosterilization of M.domestica using trgumuron 99

systems or sterile insect technique, the potential for effective and efficient suppression of pest populations by autosterilization is, in some respects, much greater, since not only can the sterilized individuals not reproduce, the equivalent to killing, but the steri- lized individuals can also decrease the reproductive output of the remaining, normal, individuals in the population because any cross between a sterilized and a normal fly will produce non- viable progeny.

The effectiveness of autosterilizing systems would be greatly enhanced by the identification of chemicals that were capable of affecting both males and females (Langley & Weidhaas, 1986; Wall & Howard, 1995). For example, simulation models have shown that for M.domestica, if females alone are sterilized, a minimum of 43% of females would need to be affected per day before suppression of the housefly population could be achieved. In contrast, if males could also be sterilized or could pass on a sufficient sterilizing dose by contact with normal females, only 25% of the population would need to be affected per day. This is because, in addition to the 25% of females sterilized directly, a further one out of every four males attempting to obtain a mating with each of the remaining fertile females would be obtained by a sterile male, assuming that sterile and unsterilized males are equally competitive. Thus, of the 75% of females not sterilized directly, a quarter would be expected to be sterilized by mating with a sterile male. As a result, a total of 44% females are effec- tively sterilized, resulting in a decline in the population (Wall & Howard, 1994). Hitherto, the lack of agents capable of steriliz- ing both sexes and which were safe for non-target organisms and the difficulty of getting flies to pick-up effective doses with real- istic contact times and at practicable chemosterilant concentra- tions, have prevented the exploitation of autosterilizing systems for housefly control.

The results reported here demonstrate that exposure of female M.domestica to triflumuron on sucrose-baited targets induces significant transovarial ovicidal and larvicidal effects and that, following exposure, males are also capable of affecting the re- productive performance of unexposed females. Direct effects on females may be a result of ingestion of triflumuron combined with tarsal contact allowing absorption of the chemical across the cuticle. The effects of triflumuron on males may also be di- rect, through impairment of spermatogenesis or insemination ability. Alternatively, exposed males may simply pick-up suffi- cient triflumuron on their bodies to allow them to pass on an effective dose to normal females during mating, as has been ob- served previously with juvenile hormone analogues in the bug Pyrrhocoris apterus (Masner et al., 1968). The exposure of males alone to the triflumuron-treated targets clearly was not as effec- tive as exposure of females alone, because, had this been the case, treatments 2 and 3 would have resulted in identical levels of egg or larval mortality. The precise mechanism through which male exposure to triflumuron is able to impair female fertility following mating requires further investigation. However, the results clearly demonstrate the additive advantage of affecting both sexes when compared to sterilizing or killing a single sex.

The net rate of increase of house fly populations in poultry houses has been estimated to be approximately 35-fold per gen- eration (Wall & Howard, 1994). In the present study, for 5 days after the 24 h exposure of both sexes to triflumuron, egg hatch was reduced to less than 4%. For those larvae that did eclose,

less than 3% pupariated, giving a cumulative mortality of 98.8%. If maintained, therefore, this level of mortality would be suffi- cient to suppress a field population of house flies. However, the percentage egg hatch and pupariation increased significantly with time elapsed after exposure. Between 6 and 10 days after expo- sure, in treatment 1 cumulative mortality had fallen to 85% and, beyond 16 days to only 70%, despite the fact that both sexes had been exposed to triflumuron. Cumulative mortality in the con- trols was 49%, 27% 44% and 57% over days <5,6-10, 11-15 and 16 respectively. Thus, the effect of a 24 h period of expo- sure to triflumuron is transitory. However, previous work has shown that sustained exposure to triflumuron-dosed targets can maintain high levels of sterility (Howard & Wall, 1995h). Hence, for effective autosterilization, continuous exposure to the triflumuron-treated targets would be required to ensure the necessary mortality. The advantage of a target delivery system is that it allows the triflumuron to be presented in a discrete package, minimizing the possibility of exposure for non-target insects. In conclusion therefore, the results suggest that sucrose-baited targets, dosed with a low concentration of triflumuron, could form the basis of an effective autosterilizing system for house fly control.

Acknowledgments

Financial support from Bayer AG and a Royal Society Univer- sity Research Fellowship to R. Wall are gratefully acknowledged. We thank Professor P. A. Langley for helpful comments on the manuscript.

References

Axtell, R.C. (1970) Integrated fly control program for caged-poultry houses. Journal of Economic Entomology, 63,400-405.

Axtell, R.C. & Arends, J.J. (1990) Ecology and management of arthro- pod pests of poultry Annual Review ofEnromology, 35, 101-126.

Chapman, P.A., Learmount, J., Morris, A.W. & McGreevy, P.B. (1993) The current status of insecticide resistance in Musca domestica in England and Wales and the implications of housefly control in intensive animal units. Pesticide Science, 39, 225-235.

Drummond, R.O., George, J.E. & Kunz, S.E. (1988) Contra[ of Arrhro- pod Pests of Livestock a Review of Technology. CRC Press, Florida.

Hammann, I. & Sirrenberg, W. (1981) Laboratory evaluation of SIR 85 14, a new chitin synthesis inhibitor of the benzoylated urea class. Pflanzenschutz-Nachrichten Bayer, 33, 1-34.

Howard, J.J. &Wall, R. (1995a) The effects of triflumuron, a chitin syn- thesis inhibitor, on the house fly, Musca domestica (Diptera: Muscidae). Bulletin of Entomological Research, 81,7 1-71.

Howard, J.J. &Wall, R. (1995b) The use of triflumuron on sugar-baited targets for autosterilization of the house fly, Muscn domrstictr. Entomologia Experimentalis et Applicara, (in press).

Knapp, F.W. & Herald, F. (1983) Mortality of eggs and larvae of the face fly (Diptera: Muscidae) after exposure of adults to surface treated with BAY SIR 85 14 and Penfluron. Journal of Economic Entomology, 76, 1350-1352.

Knapp, F.W. & Cilek, J.E. (1988) Mortality of eggs and larvae obtained from house flies (Diptera: Muscidae) exposed to triflumuron residues. Journal of Economic Entomology, 81, 1662-1 664.

0 1996 Blackwell Science Ltd, Medical and Veterinary Entomology 10: 97-100

100 Julia Howard and Richard Wall

LaBrecque, G.C., Smith, C.N. & Meifen. D.W. (1962) A field experi- ment in the control of houseflies with chemosterilant baits. Journal of Economic Entomology, 55,44945 1.

LaBrecque, G.C. & Meifen, D.W. (1966) Control of house flies (Diptera: Muxidae) in poultry houses with chemosterilants. Journal of Medi- c ~ r l Etirornologj. 3, 232-236.

Lancaster. J.L.. Jr & Simco, J.S. (1969) House fly control by chemical sterilization with apholate. Arknrzsas Experimental Station Bulletin, 737. 1-12.

I~ngley . P.A. bt Weidhaas, D. (1986) Trapping as a means of controlling tsethe. the relative merits of killing and sterilization. Bulletin ofEnto- mo/o,qical Research. 76, 89-95.

Masner. P.. Slama. K . & Landa, V. ( 1968) Sexually spread insect sterility

induced by the analogues of juvenile hormone. Nature, 219,395-396. Morgan, P.B., Weidhaas, D.E. &Patterson, R.S. (1981) Programmed re-

leases of Spalangia endius and Muscidijiurax raptor (Hymenoptera: Pteromalidae) against estimated populations of Musca domestica (Diptera: Muscidae). Journal of Medical Entomology, 18, 158-166.

Peck, J.H. & Anderson, J.R. (1970) Influences of poultry manure re- moval schedules on various Diptera larvae and selected arthropod predators. Journal of Economic Entomology, 63, 82-90.

Wall, R. & Howard, J.J. (1995)Austosterilization of the housefly Muscu domestica. Journal of Theoretical Biology, 171,431437.

Accepted 19April 1995

0 1996 Blackwell Science Ltd, Medical and Veterinary Entomology 10: 97-100