Sublethal Effects Of Nitenpyram On White-Backed Planthopper,Sogatella Furcifera (Hemiptera:Delphacidae)

White-backed planthopper（WBPH）,Sogatella furcifera（Horvath）（Hemiptera:Delphacidae）poses a serious threat to the safe production of rice.Evaluating the sublethal effect of chemical pesticides on S.furcifera has important theoretical and practical significance for agricultural production.At present,nitenpyram is the main pesticide to control S.furcifera,but its sublethal effect on S.furcifera has not been reported after short-term and long-term application in rice fields..Therefore,in this study,nitenpyram LC₂₅concentration was used to continuously（subculture）expose indoor sensitive populations of S.furcifera and the effects of one-or multi-generation exposure on biological characteristics,pesticides sensitivity,metabolic enzyme activity and related gene expression of S.furcifera were explored through bioassay,two-sex life table construction,detoxification enzyme activity determination,and RNAi,then the sublethal effect of nitenpyram on S.furcifera was systematically evaluated.The main results of this paper are as follows:1.Establishment of the sublethal effects of nitenpyram on S.furcifera population under multi-generation exposureThe LC₅₀and LC₂₅values of nitenpyram for indoor sensitive populations of S.furcifera were determined by the rice-seedling dip method.The 3rd instar nymph of F₀generation of S.furcifera was treated with nitenpyram LC₂₅concentration as sublethal concentration.After 4 days,the surviving test insects were transferred to nontoxic fresh rice seedlings for breeding and breeding to obtain F₁generation population.The LC₅₀and LC₂₅values of the F₁generation of S.furcifera were determined by the same method as above,and the 3rd instar nymph of F₁generation was continuously treated with the new concentration of LC₂₅of nitenpyram to obtain the F₂generation.After subculturing the S.furcifera for six generations in the above way,the F₆generation test insect was obtained.The bioassay results showed that the resistance of S.furcifera to nitenpyram gradually increased with the increase of treatment generations,and the LC₅₀value increased from 1.23 mg/L in F₀generation to 7.74 mg/L in F₆generation.After six generations of treatment,the sensitivity of S.furcifera to nitenpyram decreased by 6.29 times,reaching a low level of resistance.2.The sublethal effects of nitenpyram on the biological traits of S.furcifera.under one-or multi-generation exposureThe age-stage,two-sex life table procedure was used to evaluate the sublethal effect of S.furcifera.The results showed that the fecundity value of the F₀individuals showed a significant decrease in the LC₂₅treatment group compared to control,while compared to the control,the preadult period,male adult longevity,female adult longevity,longevity,total preoviposition period,oviposition days and fecundity were significantly decreased in the F₁and F₆generations.At the same time,the development times of the 1st,3rd and 5th-instar in the F₆generation were significantly reduced compared to the control and（or）F₁generation.The estimated demographic parameters in the F₁and F₆generations observed in this study showed that the intrinsic rate of increase（r_i）,finite rate of increase（λ）and net reproductive rate（R₀）were not influenced except for a decrease in T values by the nitenpyram treatment.These results indicate that the survival,reproduction and life expectancy of S.furcifera are adversely affected by the LC₂₅concentration of nitenpyram under one-or multi-generation exposure.3.Effect of nitenpyram on insecticide sensitivity and metabolic enzyme activity of S.furciferaThe sensitivity of third instar nymphs of F₁and F₆generations of S.furcifera to nitenpyram and other chemicals was determined by the rice-seedling dip method.The results showed that,compared with the indoor sensitive population F₀generation,the sensitivity of F₁generation to nitenpyram decreased and the resistance ratio（RR）was2.21 times.At the same time,the sensitivity of F₁test insects to acetamiprid,cycloxaprid,triflumezopyrim and buprofezin decreased（CR=1.80-3.09）,but the sensitivity to other insecticides remained stable.The sensitivity of F₆generation to nitenpyram was further reduced and reached a low level of resistance（RR=6.29times）.In addition,the sensitivity to acetamiprid,cycloxaprid,triflumezopyrim and buprofezin also decreased significantly（CR>2 times）,while the sensitivity to others had no obvious change.The induction activity of nitenpyram LC₂₅concentration on three metabolic enzymes of S.furcifera was determined.The results showed that the P450 and EST activity was significantly induced by nitenpyram in the F₀and F₆.Additionally,the P450 activity was significantly higher in the F₆generation than in the F₀generation.The above results indicated that the risk of resistance of S.furcifera to nitenpyram and other insecticides increased after long-term exposure to sublethal concentration of nitenpyram.The enhancement of P450 enzyme activity may play an important role in the metabolism and resistance evolution of S.furcifera.4.Screening and preliminary study on function of P450 genes related to resistance of nitenpyram to S.furciferaQRT-PCR was used to detect the expression of P450 gene in different populations of S.furcifera treated with nitenpyram and the function of up-regulated P450 genes were verified by RNAi.The results showed that compared with the control,twelve P450 genes were significantly up-regulated in the F₀individuals after treatment for 48 h with an LC₂₅concentration of nitenpyram..In the F₆generation,six P450 genes were significantly up-regulated by nitenpyram.Among them,four P450genes（CYP4CE3,CYP417A4,CYP439A3 and CYP6FJ3）were induced to be significantly up-regulated in F₀and F₆nymphs,and the expression level of these four genes in F₆generation was significantly higher than that in F₀generation.RNAi technique was used to reduce the expression of CYP4CE3,CYP417A4,CYP439A3and CYP6FJ3 in F₆generation S.furcifera,and the sensitivity of S.furcifera to nitenpyram was restored.These results suggest that these four genes may play an important role in the detoxification metabolism and resistance formation of S.furcifera to nitenpyram.