Sublethal Effects Of Three Insecticides On Hippodamia Variegate

The applications of insecticides and natural enemies are two main measures for pestcontrol all the while, but inharmonious conflict sometimes occurs between the chemical andbiological control. In order to provide reference for rational use of pesticides, the sublethaleffects of imidacloprid, abamectin and alphacypermethrin on Hippodamia variegate weredetermined in this experiment.1. The toxicity test and determination of sublethal doses of three insecticides on Hippodamiavariegate and Acyrthosiphon pisumThe toxicity of three insecticides on H. variegate and A. pisum was tested in thelaboratory. The results show that the LC50of imidacloprid, abamectin and alphacypermethrinto H. variegate respectively were194.15,137.62and3.32mg/L, and the LC50to A. pisumrespectively were14.97,3.76and16.37mg/L. The LC20of three insecticides to H. variegateand A. pisum were determined as sublethal doses. The LC20of imidacloprid, abamectin andalphacypermethrin to H. variegate respectively were70.58,54.30and1.18mg/L, and theLC20to A. pisum respectively were4.00,1.45and4.94mg/L.2. Effects of sublethal doses of three insecticides on predation of H. variegateThe functional response models of H. variegate preying on A. pisum were all stillconformed to Holling’s type Ⅱ curve in spite of pretreated with sublethal doses of threeinsecticides; just only the parameters of models had some changes. The discovery ratesdecreased, and the handling time prolonged, and the maximal predatory capacities reduced.Besides, the predatory rates and searching efficiency reduced in various degrees. Amongthree insecticides, the effects of alphacypermethrin on H. variegate were maximum whilethem of imidacloprid were minimum. The effects were related to the exposure route ofpredators obtained toxin. After preying A. pisum treated with alphacypermethrin, thefunctional response of H. variegate became weak easier. But the treatments of abamectin andimidacloprid showed opposite results.3. Repellent and antifeedant effects of sublethal doses of insecticides on H. variegateThe sublethal doses of imidacloprid and abamectin had repellent effect to H. variegatewhile the sublethal dose of alphacypermethrin displayed no deterring activity. The sublethal doses of three insecticides all had choice and no-choice antifeedant effects to H. variegate.4. Effects of sublethal doses of three insecticides on the developmental duration andmultiplication of H. variegateThe oviposition of F0generation of H. variegate pretreated with sublethal doses of threeinsecticides all reduced. The daily average oviposition of H. variegate pretreated withsublethal doses of three insecticides by contact methods was significant differences comparedwith control. The accumulative average oviposition of H. variegate pretreated with sublethaldoses of imidacloprid and abamectin by contact methods was significant differencescompared with control. The oviposition of other treatments was no significant differencescompared with control.The hatching rates of the eggs laid by H. variegate first day were allsignificant lower than that of control. The total developmental duration from egg to pupa ofthe F1generation of H. variegate pretreated with sublethal doses of three insecticides bycontact methods significantly prolonged, but the total developmental duration of thetreatments by feeding methods was no significant differences compared with control. Theeffects of sublethal doses of three insecticides on the oviposition and hatchability of the F1generation of H. variegate declined; just only the hatching rates of treatment withalphacypermethrin by contact methods was significant differences compared with control. Onthe whole, the effects of contact methods to H. variegate were stronger than feeding methodsin this experiment.