Sublethal Effects And Mechanisms Of Biopesticides On The Predator Cyrtorhinus Lividipennis Reuter(hemiptera: Miridae)

Cyrtorhinus lividipennis(Reuter)(Hemiptera:Miridae)is an important predatory in the rice paddy.It mainly feed on the eggs and young nymphs of brown planthopper(Nilaparvata lugens).In this study,the selective toxicity of seven commercial biopesticides for C.lividipennis was examined under laboratory conditions.Three biopesticides(matrine,abamectin and azadirachtin)were selected to study the effects of their sublethal concentration(LC10 and LC20)on C.lividipennis.The internal mechanisms of abamectin on the reproduction of C.lividipennis were investigated.The results were as follows:(1)Abamectin was the most selective to C.lividipennis,followed by matrine and azadirachtin.Veratridine,rotenone,Bacillus thuringiensis and Beauveria bassiana showed less selectivity for C.lividipennis.C.lividipennis treated with sublethal concentrations(LC10 and LC20)of the three biopesticides could distinguish volatiles released from healthy and N.lugens-infested plants indicating that the biopesticides tested did not affect the foraging ability of surviving miridbugs.Azadirachtin decreased the consumption capability of C.lividipennis when the densities of N.lugens were 20,30,40 and 50 insects per vial.Sublethal concentration treatment did not impact the pre-oviposition period or egg hatchability of C.lividipennis.However,the fecundity of C.lividipennis exposed to azadirachtin and abamectin increased by 27-41%compared to the untreated individuals.(2)We cloned phosphoinositide 3-kinase(ClPI3K)and serine/threonine kinase(ClAkt)in C.lividipennis.In our studies,no significant difference for JHAMT and JHE were observed in the regulatory subunit of PI3-kinase(ClPI3K1)or catalytic subunit of PI3-kinase(ClPI3K2)-silenced females compared with the dsGFP-injected controls.A significant reduction in mRNA expression levels was observed for ClVg in the CIPI3K1 and ClPI3K2-silenced females.The numbers of eggs laid by C.lividipennis in the CIPI3K1 and ClPI3K2-silenced females were 29.1 ± 3.8 and 34.7 ± 2.7 eggs/female,respectively,which were 51%and 41%lower than the control(59.1±4.8 eggs/female).CIPI3K1 and ClAkt were up-regulated at 2,4 and 6 days after abamectin treatment compared to the control groups.Furthermore,CIPI3K1 knockdown significantly reduced ClVg expression which is previously up-regulated after abamectin treatment.