Sublethal Effects Of Fipronil On Agrotis Ipsilon

Agrotis ypsilon is an important agricultural pest in our country.The control of A.ypsilon is mainly based on chemical control at present.However,incorrect application time and method have led to the control failure.Fipronil as a seed coating insecticide in northern dry fields,whether the sublethal dose of fipronil have an impact on A.ypsilon larvae after its application in the field.In this study,the effects of sub-lethal concentrations of fipronil on the growth and development of A.ypsilon,fertility and soil depth were studied,and the physiological and biochemical indexes and enzyme activities of A.ypsilon were determined.The sublethal effects of fipronil on the larvae of A.ypsilon were investigated.The main research results are as follows:1.The acute toxicity of fipronil to the 3rd instar larvae of A.ypsilon was determined by leaf dipping method,and the LC₅₀value was 6.637mg/L.The values of three sub-lethal concentrations,LC₅,LC₁₀and LC₂₅,were determined to be 1.836mg/L,2.438mg/L and3.918mg/L,respectively.2.Under the sub-lethal concentrations of LC₅,LC₁₀and LC₂₅,the pupation rate,pupal stage,pupal emergence rate,egg hatching rate and lifespan of female adult larvae were significantly decreased,pupal weight was increased,pupal time and developmental duration of larvae in each instar were significantly extended,while the egg hatching rate and male/female ratio were not significantly different compared with the control group.After treatment with three sub-lethal concentrations of fipronil,the average single female fecundity of A.ypsilon decreased gradually with the increase of treatment concentration.The average number of single female eggs in LC₅treatment group was decreased by 20.60%compared with control group.The eggs laid by single female in LC₁₀treatment group and LC₂₅treatment group were decreased by 26.92%and 31.65%compared with the control group,respectively.The eggs laid peak of A.ypsilon was delayed after treatment with three sub-lethal concentrations.The daily maximum oviposition of single female was increased in LC₁₀and LC₂₅treatment groups,but decreased in LC₅treatment group.The oviposition duration of LC₅and LC₁₀treatment groups was shortened,and the oviposition duration of LC₂₅treatment group was significantly longer than that of control group.3.The content changes of reactive oxygen species（ROS）,malondialdehyde（MDA）and other substances and the activity changes of protective enzymes in the larvae were measured.The results showed that the content changes of ROS and MDA in the larvae at different time periods had a certain time effect.The accumulation of both also gradually increased in the body of A.ypsilon.At the same time,the activity of the three protective enzymes also changed to a certain extent,the SOD activity in the body of the F₀generation of A.ypsilon showed a trend of decreasing first and then increasing,and reached the lowest level after 24h treatment.The SOD activity in F₁generation larvae was inhibited to a certain extent,and the overall trend was decreased.At 12h and 72h,POD activity increased gradually with the increase of treatment concentration,however,the difference was not significant compared with the control.The variation trend of POD activity in F₁generation was very similar to that of in F₀generation,which had a certain induction effect on POD activity in F₁generation.During the treatment period,the CAT activity of the larvae in the control group was lower than that of in the fipronil sub-lethal concentration groups,and the CAT activity of the larvae in the F₁generation showed an increasing trend.At 12h,LC₂₅concentration treatment group was significantly different from control group,and fipronil could cause certain oxidative damage to A.ypsilon.4.It was found that after three sub-lethal concentrations of fipronil treatment,the pupation depth in soil of F₀and F₁generations was affected,and the pupation depth of larvae of F₁generation was significantly increased,and the change was more significant.The pupation depth of larvae of LC₂₅concentration treatment group was higher than that of in the control group by 45.03%.The sub-lethal concentrations of fipronil treatment increased the difficulty of pupae emergence due to the deeper of pupation depth.