Effects Of Low Concentrations Of Sulfoxaflor And Imidacloprid On Longevity,Fecundity,Predation Function And Flight Potential Of Hippodamia Variegata

Hippodamia variegata Goeze is one of the most common natural enemies in cotton fields,which plays an important role in the ecological control of A.gossypii.However,the use of insecticides often has a negative impact on natural enemies in cotton production.When insecticides are sprayed into cotton field,they will be affected by climate or biological factors such as light and rainfall,and the concentration of insecticides will gradually decrease.When natural enemies contact or ingest this low concentration of insecticides,they will produce sublethal effect,which is not conducive to the integrated management of A.gossypii in cotton fields.The dipping method was used by us to test the toxicity of imidacloprid and sulfoxaflor against A.gossypii,and the sublethal concentration(LC₂₀,LC₅₀)was obtained as the concentration of the agent for treating female H.variegata according to the results of toxicity test.By providing female H.variegata with contaminated A.gossypii,the sublethal effects of the two insecticides on the survival,life parameters,predation function and flight capacity of female H.variegata were evaluated through contact treated-leave and ingest treated-aphid.The main results are as follows:（1）The LC₂₀concentrations of the two insecticides had no significant effect on the survival rate of female H.variegata,but that of LC₅₀significantly reduced the survival rate of female H.variegata,and had obvious toxicity on female H.variegata.Besides,the safety of sulfoxaflor at LC₅₀concentration was significantly better than imidacloprid.The survival rate of LC₅₀concentration of imidacloprid was the lowest.Sulfoxaflor is safer than imidacloprid.（2）The sublethal concentrations of the two insecticides had a significant negative impact on the life parameters of female H.variegata.In terms of longevity and survival curves,both the LC₂₀and the LC₅₀concentration of imidacloprid significantly shortened the longevity of female H.variegata,while the sublethal concentration of sulfoxaflor had no significant effect on the longevity of H.variegata.At the same time,the sublethal concentration of imidacloprid reduced the survival curve of female H.variegata sharply,but the survival curves of treatment groups of sulfoxaflor were similar with control group,and there was no significant difference between them.In terms of reproduction,sublethal concentration of imidacloprid and sulfoxaflor significantly prolonged the pre-oviposition period of females and reduced the fecundity of females as well.In terms of longevity of female adults,sulfoxaflor had higher safety than imidacloprid;in terms of fecundity,sulfoxaflor had less impact than imidacloprid,but the difference was not significant.（3）The sublethal concentrations of the two insecticides had a significant negative impact on the predation function of female H.variegata.Under the treatment of sublethal concentrations of the two insecticides,the predation function of female H.variegata to A.gossypii conformed to the HollingⅡequation model.The treatment groups(LC₅₀)of the two pesticides had the highest instant attack rate followed by the control group,while treatment group(LC₂₀)was the smallest.The treatment group of sulfoxaflor(LC₂₀)had the smallest handing time,predation capacity and daily maximum predation number.The treatment group of imidacloprid and sulfoxaflor of LC₅₀concentration had the longest handing time while the smallest predation capacity and daily maximum predation number.The LC₂₀concentration of sulfoxaflor increased the predatory effect of female H.variegata on A.gossypii.At the LC₅₀concentration,the two insecticide treatments both reduced the predation ability and daily maximum predation number of female H.variegata.In terms of predation function,sulfoxaflor had less effect on female H.variegata than imidacloprid.（4）Through analysis of the total flight distance,cumulative flight time,average flight speed in each treatment groups of two insecticides sublethal concentration,the results indicated that the sublethal concentrations of the two insecticides significantly shortened the total flight distance of female H.variegata.The accumulated flight time was reduced,but the effect on average flight speed was not significant.The flight parameters of the sublethal concentration of imidacloprid in each treatment group were lower than the treatment group of the same concentration of sulfoxaflor.However,their differences were not significant.At the same time,the analysis of the maximum flight distance and maximum flight speed of female H.variegata showed that the treatment groups(LC₂₀and LC₅₀)of imidacloprid were lower than the control group and the treatment groups of sulfoxaflor.Treatment groups(LC₂₀and LC₅₀)of imidacloprid were significantly reduce compared with the control group,and difference was not significant compared with the sulfoxaflor treatment.Compared with imidacloprid,sulfoxaflor had less effect on flight capacity of female H.variegata.In this study,the effects of sublethal concentrations of imidacloprid and sulfoxaflor on survival,fertility,predation and flight of female H.variegata were clarified,and the safety of sublethal concentrations of two insecticides on female H.variegata was compared.The results of study are helpful to guide the rational use of pesticides in cotton field,and provide a scientific basis for the protection of H.variegata.Then H.variegata can play a greater role in pest control in farmland ecosystem.