Study On The Larval Feeding And Adult Oviposition Preference Of Two Synanthropic Fly Species

Scarcity and cost of fish meal as a livestock and commercial fish food has increased the need to find alternative plant and animal protein based foods.Fly larvae are used to produce Magmeal.This food supplement has high nutritional value and has successfully replaced fishmeal in the diet of animals.However,popularization of the magmal in the poulry and fishery is faced with problem of the high cost of the diet of the fly larvae.To improve the chemical and physical characters of the fly diet,in this paper,we designed several tests to reveal the mechanisms of the larval feeding and adult ovipositionpreference of Musca domestica L.(MD) and Chrysomya megacephala(F.)(CM). In the first test,larval food preferences,development,and oviposition preference of 10-15 days old MD and CM were evaluated on three substrates:wheat bran,pork muscle, and fish meal.Pork muscle was the optimal food for both species.MD larvae completed development on the wheat bran,but CM did not.In choice tests,the second instar CM larvae preferred pork muscle to wheat bran(p<0.05),while second instar MD larvae showed no preference.Female CM predominantly chose pork muscle as-the oviposition substrate.Female MD laid eggs on three substrates and wheat bran showed the greatest attrativeness to gravid MD(p<0.01).The second test is to evaluate the larval nutrition resource competition between the F₁ larvae of CM and MD wild populations.The results indicated that the extreme nutrition restriction produced shorter MDor CM pre-adult development time,but MD or CM exhibited longer pre-adult development time and lower body weight and smaller size of following adults when larvae were reared on nutrition substrates with varying protein contents(p<0.05).CM larvae exhibited stronger resource competition potential than MD larvae on nutrition materials with the content of protein >6.4%.The development of second or third instar CM larvae on wheat bran could be improved significantly when reared with second or third instar MD larvae,which would help CM to extend their ecological niches into plant materials.The second instar CM larvae could enter into the pupal state on the wet bran with the water content of 45-75%,but the first instar MD only grew normally on 55-75%water content of wet wheat bran.The F₁ females of MD and CM all preferred to lay their eggs on the mixtures of the wheat bran and pork muscle than wheat bran or pork muscle.With the increasing of animal protein substrates in garbage in the urban-suburban areas,CM has the potential of displacing the established house fly from this ecological niche in some urban-suburban areas.The third test was to evlaute the effect of the chemical and physical character of the oviposition substrate,the age of the female and existence of the conspecific larvae on the oviposition preference of female and/or MD and/or CM.Female MD significantly preferred ovipositing on wet wheat bran with the water content of 60%or with a particle size of > 2.0 mm dia(p<0.01).In the two-choice olfactometer,wheat bran or pork muscle was more attractive to female and male MD or CM than distilled water(p<0.01),and pork muscle showed greater attractiveness to female and male MD or CM than wheat bran (p<0.01).Female CM was more attracted by pork muscle than male CM(p<0.05),which was not found in MD(p>0.05).The acceptability of wheat bran to gravid CM was not enhanced with the addition of different acid aminos and MD females did not lay more eggs on pork mucle when glucose,sucrose and starch were added.MD females did not lay more eggs on the wheat bran with the existence of conspecific larvae.But the food which had been ingested by conspecific larvae showed greater attractiveness to female MD or CM than fresh food.During the whole oviposition period,age had no significant effect on the oviposition preference of MD and CM.MD females laid more eggs on wheat bran than on fishmeal and pork muscle(p<0.01),and CM females always laid their eggs on pork muscle.The fourth test are to evaluate the effects of larval experience on larval feeding preference and the effects of larval and pupal experience on oviposition preference of females in MD and CM.Dietary experience since hatch to test could significantly influence feeding preference of the second instar larvae in MD(p<0.01),but could not in CM.The larval dietary and pupal experience did not change the oviposition preference of CM and experienced gravid females laid all of their eggs on pork muscle.Larval feeding regimen had no effect on oviposition preference of subsequent females in MD.However, the pupal experience in MD significantly influenced the oviposition preference of subsequent females,and MD females from pupae matured on wheat bran laid significantly more eggs on wheat bran than that matured on pork muscle or filter paper whether pupae were washed or not(p<0.01).These results demonstrated that host-selection behavior in MD was shaped by preimaginal experience according to the chemical legacy hypothesis.In the last test,the fine structure of the ovipositor and tarsi of front,middle and hind legs of female MD were studied using scanning electron microscopy to contribute detailed morphological information on these organs of this species.Several types of sensilla were found on the tarsi,hypoproct,epiproct and cercus,including the sensilla bristle,sensilla chaetica,sensilla trichodea,sensilla basiconica,sensilla coeloconica and sensilla cavity. The bristle,sensilla chaetica and sensilla trichodea with typical morphological characters of mechanoreceptors may provide mechanical information of the oviposition substrate. The sensilla styloconica on the terminal of the dorsal side of the left cercus may serve as hydroreceptor of females.