Sublethal Effects Of Two Insecticides Against Paracoccus Marginatus (Hemiptera:Pseudococcidae)

Paracoccus marginatus is one of the most dangerous mealybugs in subtropical and tropical areas.It is native to Mexico and has invaded Taiwan,Guangdong,Hainan,Yunnan and Fujian.Its host can reach up to264 species in 68 families,which poses a serious potential threat to economic crops and ornamental plants.Chemical control has always been the most rapid and efficient method in pest control.After the use of chemical agents,their toxicity in the environment will gradually decrease to sublethal dose,resulting in sublethal effects on the growth and development of insects and metabolic enzymes in the body.In this study,two insecticides,chlorfenapyr and lambda-cyhalothrin,were screened out from 16 insecticides.These two kinds of pesticides are widely used in the control of fruit tree pests because they are more registered pesticide products and have been used for a long time.However,while other pests were being controlled in the orchard,the new invasive pest,P.marginatus,as a non-target,was highly susceptible to sublethal dose.Therefore,the sublethal effects of chlorfenapyr and Lambda-cyhalothrin on P.marginatus were determined by two sex life table and enzyme assay in order to provide theoretical basis for chemical control of P.marginatus.The main research results are as follows:1.Insecticides screening for the control of P.marginatusIn this study,five insecticides,chlorfenapyr,lambda-cyhalothrin,beta-cyhalothrin,pyridaben and tolfenpyrad,were selected from 16insecticides by dipping method.Among them,P.marginatus has the highest sensitivity to chlorfenapyr and lambda-cyhalothrin.The toxicity regression equation of chlorfenapyr was y=3.26+1.63 x,LC₁₀ was 1.904mg/L,LC₃₀ was 6.064 mg/L,and the toxicity regression equation of Lambda-cyhalothrin was y=5.35+0.58 x,LC₁₀ was 0.001 mg/L,LC₃₀was 0.03 mg/L.2.Effects of chlorfenapyr and lambda-cyhalothrin sublethal concentrations on detoxifying enzymes and protective enzymes of P.marginatus.The sublethal concentrations of chlorfenapyr and lambda-cyhalothrin,LC₁₀ and LC₃₀,were determined and analyzed for 24h and 48 h after treating the 2nd instar nymphsnymphs of P.marginatus.Changes in the detoxifying enzymes Ach E and CarE and protective enzymes SOD,CAT and POD activities in the 2nd instar nymphsof P.marginatus showed that:（1）The toxic effect of chlorfenapyr on the 2nd instar nymphsof P.marginatus inhibited the activities of CAT and CarE,while the activity of SOD and AChE increased,and the promotion effect of LC₁₀ treatment group was higher.However,the activities of POD were differences in the time and concentration,which showed that the activity of LC₁₀ treated group was higher than that of LC₃₀ treated group,and the activity of LC₁₀treated group was decreased during the 24 h hour of pesticide treatment.This indicates that SOD,POD and AChE in the 2nd instar nymphs of P.marginatus may be involved in the process of detoxification metabolism to chlorfenapyr,and the lower the concentration,the stronger the detoxification ability,while CAT and CarE are not involved.AChE may be the target enzyme of P.marginatus to chlorfenapyr.（2）The activity of POD in the 2nd instar nymphsof P.marginatus treated with lambda-cyhalothrin was firstly increased and then decreased.The activities of CAT were decreased in LC₁₀ treatment group,but increased in LC₃₀ treatment group.The activity of SOD did not change after 24 h treatment,but increased after 48 h treatment.The activity of AChE increased in LC₁₀ treatment group after 24 h treatment,and increased in LC₃₀ treatment group after 48 h treatment,but returned to normal level in LC₁₀ treatment group.The CarE activity was decreased after 24 h treatment,and the LC₁₀ treatment group returned to normal after 48 h treatment.The results showed that SOD,POD,CAT and AChE in the 2nd instar nymphs of P.marginatus were involved in the degradation of lambda-cyhalothrin toxicity,while CarE is not involved.AChE may be the target enzyme of P.marginatus to lambda-cyhalothrin.3.Effects of chlorfenapyr and lambda-cyhalothrin sublethal concentrations on the two sex life tables of P.marginatus.In this study,the two sex life tables of F₀ and F₁ generations of P.marginatus were constructed by sublethal concentration of chlorfenapyr and lambda-cyhalothrin.The results showed that chlorfenapyr and lambda-cyhalothrin had different effects on the development,reproduction and population of P.marginatus in different generations.The main findings are as follows:（1）Chlorfenapyr treatment group compared with the CK,the developmental duration and life span of F₀ generation of P.marginatus were significantly prolonged,and the survival rate,life expectancy and predicted population size were significantly reduced in the chlorfenapyr treated group,but the fecundity,net reproductive rate（R₀）,intrinsic rate of increase（r）and finite rate of increase（λ）were no significant changes.The development duration and the life span of male of F1 generation were significiantly extended,and the fecundity was no significant changes,but the survival rate,life expectancy and predicted population size were significantly reduced,and R₀,r andλwere significantly lower than those of CK.The development duration and life span of F₃generation were significantly reduced,and the survival rate,,life expectancy and population predicted size were significantly increased.There was no significant change of feculence,R₀,r andλ.Compared with F₀,F₁ and F₃ generations in the chlorfenapyr treated group,the developmental duration of P.marginatus was prolonged gradually,and the life span,fecundity and life expectancy decreased significantly at first and then increased significantly（F₀<F₁<F₃）,survival rate,predicted population size,r andλfirst decreased and then increased（F₁<F₃<F₀）.（2）Lambda-cyhalothrin treatment group compared with the CK,the development duration and life span of F₀ generation of P.marginatus were not significantly changed,but the survival rate was decreased,and the fecundity,life expectancy and predicted population size were significantly increased,but R₀,r andλwas no significant change.There was no significant change in the developmental duration and life span of F₁ generation.The survival rate,life expectancy and predicted population size of F₁ generation decreased,but fecundity,R₀,r andλdid not change significantly.The development duration of F₃ generation decreased,the survival rate increased,the predicted size of population decreased,and the fecundity,life span,life expectancy,R₀,r andλdid not change significantly.Compared with F₀,F₁ and F₃ generations in the lambda-cyhalothrin treated group,the development duration and the life span of F₀ generation of P.marginatus were significantly prolonged（F₀<F₁<F₃）,the survival rate and fecundity were decreased（F₀<F₁<F₃）,life expectancy first increased and then decreased（F₃<F₀<F₁）,and the predicted population size,r andλdecreased gradually（F₀<F₁<F₃）.In conclusion,in this study,five kinds of highly sensitive insecticides were screened out through the toxicity test in laboratory,which can provide a certain reference basis for the control of P.marginatus.Furthermore,the sublethal effects of chlorfenapyr and lambda-cyhalothrin on P.marginatus were systematically analyzed,which provided a theoretical basis for the correct evaluation of the potential of chlorfenapyr and lambda-cyhalothrin in the control of P.marginatus.