Research On The Non-lethal Effects Of Imidacloprid On Aphidphagous Ladybeetle Harmonia Axyridis

Harmonia axyridis,a polyphasic natural enemy,is directly and indirectly affected by pesticides applied in the field.Non-lethal effects such as sublethal concentration of insecticides that survive under the action of insecticides will be eaten by Harmonia axyridis,causing the Harmonia axyridis to act slowly and stunt,which should be considered in the safety assessment of insecticides;In addition,individuals with different background colors and spot patterns may have differences in stress resistance and predation control functions,studying the effect of sub-lethal concentration of insecticides on the inheritance of Harmonia axyridis spot pattern helps to illuminate the exact mechanism of non-lethal effects.In this experiment,soybean aphids treated with a sublethal concentration(LC₂₅)of imidacloprid were fed to Harmonia axyridis,and the developmental duration,survival ratio,pupal weight and functional predatory response of different developmental stages of Harmonia axyridis were measured,the genetic diversity of color spots of Harmonia axyridis was analyzed,and the changes of enzyme activity in Harmonia axyridis were studied.The effect of imidacloprid at sublethal concentration on the induction of Harmonia axyridis was evaluated,which is of great significance to the protection and utilization of Harmonia axyridis in the future.The main research results of the experiment are as follows:?1?Imidacloprid had a significant effect on the developmental duration,pupal weight and survival ratio of Harmonia axyridisRegardless of the developmental stage of the G₀ generation of Harmonia axyridis that was fed imidacloprid treated aphids,their development duration was significantly prolonged and their pupal weight and survival ratio were significantly reduced?P<0.05?;The medicament also has a certain effect on the survival ratio,indicating that the sublethal concentration of imidacloprid has a greater gastric toxicity on the third nutritional level of Harmonia axyridis.Irrespective of whether the 1st,3rd or 4th instar larvae of the G₀ generation was the first to feed on imidacloprid treated aphids,the3rd instar larvae period of the G₁ generation was significantly extended,and the 4th instar larvae period was significantly shortened;When the 4th instar larvae of the G₀ generation was the first to feed on imidacloprid treated aphids,the developmental duration of the G₁ generation was significantly extended from the 1st to the 3rd instar larvae?P<0.05?;in all treatment groups,the pupal weight of the G₁ generation decreased,but the survival rate of larvae at each age did not change significantly.?2?Imidacloprid reduces predation of Harmonia axyridisThe predation response of the Harmonia axyridis on soybean aphids treated with sublethal concentration imidacloprid and the non-medicated ladybugs in various stages conformed to the Holling II Disc equation.Feeding Harmonia axyridis imidacloprid treated aphids significantly reduced the maximum predation rate of the 2nd,3rd and 4th instar larvae lower than that of the control group?P<0.05?.The sub-lethal concentration of imidacloprid reduced the predation of Harmonia axyridis,thus affecting the population control function of Harmonia axyridis.?3?Imidacloprid has a significant effect on genetic diversity of color spots of Harmonia axyridisBoth black-spotted and yellow-spotted Harmonia axyridis can be stably inherited in the offspring,but there are no specific rules.The sub-lethal concentration of imidacloprid significantly increased the number ratio of G₁ generation black-spotted 2 window in Harmonia axyridis and significantly reduced the number ratio of 17 and 19 spots?P<0.05?.The sub-lethal concentration of imidacloprid has a significant effect on the background color of Harmonia axyridis,significantly reducing the yellow-type ratio of the G₁ generation and significantly increasing the black-type ratio of the G₁ generation?P<0.05?.The effect of sub-lethal imidacloprid on different background colors of the G₁ generation Harmonia axyridis was significant?P<0.05?.The effect of sub-lethal imidacloprid on different sex and same background colors of the G₁ generation Harmonia axyridis was non-significant?P<0.05?.?4?Imidacloprid has a significant effect on the enzyme activities of different stages of Harmonia axyridisThe imidacloprid treatment significantly increased the specific activity of GST in the Harmonia axyridis,which was significantly higher in the LC₂₅ treatment group than in the control group at 1st,3rd and 4th instar larvae?P<0.05?.Imidacloprid treatment significantly increased the expression of GST in 1st,3rd and 4th instar larvae of Harmonia axyridis.Imidacloprid treatment significantly increased the expression of SOD in the 1st instar larvae of Harmonia axyridis,and reduced the specific activity of SOD in the 2nd and 3rd instar larvae of Harmonia axyridis,with no significant difference at other ages.Imidacloprid treatment significantly reduced the expression of CAT in the1st instar larvae of Harmonia axyridis,and increased the specific activity of CAT in the 3rd and 4th instar larvae of Harmonia axyridis,with no significant difference in other ages.The sub-lethal concentration of imidacloprid under the action of imidacloprid being eaten by Harmonia axyridis will not only cause the death of some individuals of natural enemies,but also prolong the development period and reduce the predation and control functions of Harmonia axyridis.In addition,significantly increasing the black background ratio of offspring and reducing the yellow background ratio,the difference in the repellence of prey on the two types of background ladybirds may partially explain the decline in the predation function of the population.In addition,two enzyme activities?GST and CAT?increased,and one?SOD?decreased is conclusive evidence that the ladybug will respond physiologically to sublethal concentrations of pesticides.