Effects of low doses of acetamiprid and afidopyropen on the parasitic function of Lysiphlebia japonica (Ashmead)

In order to clarify the effects of low doses of chemical insecticides on parasitic natural enemies, the effects of two low doses (LC₅ and LC₃₀) of a commonly used insecticide (acetamiprid) and a novel insecticide (afidopyropen) on the parasitic functional response of Lysiphlebia japonica (Ashmead) to Aphis gossypii Glover were determined in the present study. The results showed that the LC₅₀ of A. gossypii to acetamiprid and afidopyropen were 442.6 mg/L and 1.67 mg/L, and the LD₅₀ of L. japonica to these two insecticides were 0.007 μg/cm² and 20.58 μg/cm², respectively. After exposure to sublethal doses of insecticides, the parasitism of L. japonica showed a negative acceleration curve with the density of A. gossypii. The parasitism load of L. japonica increased gradually with the increase of A. gossypii density. The basic structure of the functional response model of L. japonica still conformed to Holling type-Ⅱ, while the parameters of the model had some changes. When A. gossypii density was 20, 40, and 100 individuals per dish, the parasitism of L. japonica was significantly lower than that of the control group except for that of L. japonica treated with LC₅ of acetamiprid, which was not significantly different from the control, and the LD₃₀ of acetamiprid had the strongest inhibition on the parasitism of L. japonica. When A. gossypii was exposed to low doses of insecticides, the parasitism time of L. japonica on A. gossypii was significantly prolonged compared to the control. Moreover, the maximum daily predation of L. japonica was significantly lower than that of the control. In addition, the searching efficiency of L. japonica was significantly inhibited by low doses of acetamiprid and afidopyropen. Our results indicated that low doses of acetamiprid and afidopyropen had negative effects on the parasitism of L. japonica, and these results help to protect and utilize natural enemies and guide the scientific and rational use of pesticides in the fields.