Sublethal Effects Of Four Low-toxicity Insecticides On Development And Reproductive Behavior Of The Diamondback Moth, Plutella Xylostella (L.)

The diamondback moth (DBM), Plutella xylostella (Lepidoptera: Plutellidae) is oneof the most serious pests on cruciferous vegetables. Due to its high possibility ofdeveloping resistance insecticides, the diamondback moth is very difficult to control. Weselected four low toxicity insecticides which have the excellent potential of controllingDBM in this research. The sublethal concentrations (LC25) of four insecticides to DBM3rdinstar larvae were determined under laboratory conditions, and the sublethal effects of thefour insecticides on DBM development and reproduction were studied.Regarding the growth and development of the diamondback moth under sublethalinsecticides treatment, the four pesticides have significantly inhibited the growth anddevelopment of the diamondback moth, but the inhibition effects varied among the fourinsecticides. Indoxacarb treatment most significantly prolonged the developmentalduration of DBM larval, the duration was1.93days longer than the control group; Whilechlorfenapyr treatment was not significantly different on the larval development whencompared with the control group on the larval development. All insecticides used in thisstudy significantly reduced DBM male pupal weight except the chlorfenapyr. The weightof female pupae were also significantly reduced with all insecticide treatment withindoxacarb treatment the most significant effect. All the selected insecticides, particularlytebufenozide and indoxacarb, significantly reduced DBM pupation rate and emergencerate.The DBM treated with sublethal concentration of four insecticides had inhibitedcalling behavior of the female moths, chlorfenapyr and indoxacarb showed the mostsignificant inhibiting effect. The calling behavior duration of these two insecticidestreatment were shorter than the control group in the first, the sixth and the seventhscotophase, and the largest difference of the calling percentage between the treatmentgroups and the control group reached nearly20%. The calling duration of tebufenozide andchlorfluazuron treatment groups were similar as the control group in all the dark periods,the calling percentage diversity was always maintained at less than10%.Although thefemale moths calling behavior effected by the insecticides treatment, there was nosignificant differences on the calling percentage between the insecticides treatment groupsand the control groups. The calling peaks of all the groups were at2.0h to3.0h intoscotophase, and females of all groups maintained the highest calling percentages for about1h or1.5h.All the selected insecticides could significantly interfere the ability of male surviveddiamondback moths to perceive sex pheromone. In the experiments which used the controlsurvive moths and sex pheromone standard as odor source, indoxacarb treated male mothshad the highest unresponsing rate and the longest average responsing time; The male moths treated with Chlorfenapyr had been most significantly interfered on the directionalselection behavior, the selective rate of this treatment male moths was less than60%. Theaverage responsing time of the male control moths to female moths treated withchlorfenapyr and indoxacarb was significantly higher than the survive female moths of theother three treatment groups, the average response time was nearly30s. The selective rateof the male control moths to female moths which treated with four insecticides wassignificantly lower than to the control female moths, however, there was no significantdifference in selectivity among insecticides treated female moths.The sublethal effects of the four insecticides on DBM reproduction were studied.Tebufenozide, chlorfluazuron and indoxacarb significantly decreased the mating successesof DBM survivals, especially inhibitory effect of tebufenozide treatment is most obvious;All the insecticides significantly reduced DBM fecundity and hatchability. In addition,DBM in tebufenozide treated group had the lowest fecundity and hatchability, andsublethal effect of the DBM hatchability in the chlorfenapyr treatment was the weakest.