Effect Of Wolbachia Infection And Its Density On The Resistance To Insecticide In Chilo Suppressalis

Food shortage is one of the most remarkable problems nowadays.A large number of people in Asia,Africa,Latin America and other developing countries are in hunger or semi starvation state.Food shortage has hindered seriously the development of the national economy of developing countries.China is the largest developing country in the world,the problems of food production and safety are even more prominent.Chilo suppressalis is an important rice pest worldwide.Over the years,the prevention and control of C.suppressalis mainly rely on monosultap insecticide control which resulting high levels of resistance to insecticide in C.suppressalis in most of the rice growing areas,The chemical control effect decreased significantly,the number of medication dosage increased and the control cost gradually increased,environmental pollution had further intensified.Therefore,resistance to insecticide in C.suppressalis has been one of the important topics in rice pest control.Wolbachia is an intracellular symbiosis that is widely distributed in insects and other arthropods,it can regulate the reproduction of the host.In addition,Wolbachia can also affect the host's sense of smell and fitness,it is considered as the most promising pest control tool.But there are very few reports on the effect of Wolbachia infection on the resistance to insecticide.In this study,we investigated the effect of Wolbachia infection and its density on the resistance to insecticide in C.suppressalis,which will provide new ideas or new methods for the control of C.suppressalis.It has a very important significance on the country's food security and environmental protection.The main contents and results are as follows:Studies on the rearing of Chilo suppressalis in lab: In this experiment,we researched the difference of the larval stage,pupation period,pupation rate,eclosionrate,oviposition rate and hatching rate under different feeding conditions(cane shoots,rice seedlings and artificial feed).The results showed that the larval stage and pupation period were the shortest when C.suppressalis were fed with artificial feed,and the oviposition rate and hatching rate were significantly higher than the other two groups(P < 0.05).There was no significant difference in the pupation rate and eclosion rate of C.suppressalis when fed with artificial feed or cane shoots(P>0.05)Which were higher than the pupation rate and eclosion rate when fed with rice seedlings.As the rice seedlings are not easy to obtain in winter,cane shoots are not easy to save,and the artificial feed better,cost lower and are easier to save.Therefore,the author believed that the use of artificial feed for indoor feeding is more scientific and effective.Infection with Wolbachia in Chilo suppressalis by embryo microinjection:Extracted hemolymph from Drosophila infected by wPopcorn(a highly virulent Wolbachia strain),and then injected the hemolymph into embryos of C.suppressalis by using the method of embryo microinjection.The growth of C.suppressalis were observed after the embryo microinjection,and we detected the infection of Wolbachia in C.suppressalis adults by PCR.The hatching rate was 28.2%,the pupation rate was26.4% and the eclosion rate was 49.3% after microinjection.The Wolbachia infection rate of C.suppressalis was 7.1%.Effect of Wolbachia infection and its density on the resistance to insecticide in Chilo suppressalis: We compared the differences on resistance to insecticides(fipronil and avermectin)between the Wolbachia infected strains and the Wolbachia uninfected strains by using topical application method.The experimental subjects were four instar larvae.There were also differences in resistance to insecticides in Wolbachia infected strains.We collected the larvae of different survival time under0.2mg/L fipronil treatment,extracted their DNA to determine the relative content of Wolbachia.The experimental groups were the C.suppressalis died in 24 h,48h and72 h.The control group was the C.suppressalis died in 12 h.The target gene was the surface protein gene wsp of Wolbachia and the reference gene was 18 S RNA.Fluorescent quantitative PCR was used to measure the relative contents of Wolbachia in C.suppressalis at different survival time.The results showed the average death number of C.Suppressalis infected with Wolbachia were significantly lower than that of uninfected Wolbachia strains under the treatment of fipronil and avermectin(P<0.05).The median lethal dose of fipronil of Wolbachia infected strains was 20 times than that of Wolbachia uninfected strains.And the median lethal dose of avermectin of Wolbachia infected strains was 9.5 times than that of Wolbachia uninfected strains.The results showed that Wolbachia infection significantly enhanced the resistance to fipronil and abamectin in C.Suppressalis.The relative ratio of Wolbachia content of survial C.suppressalis in 72 h was 2.3 times than 12 h under 0.2mg/L fipronil treatment,which significantly higher than 24 h and 48h(P<0.05).The results showed that the higher density of Wolbachia the longer they live.The resistance of C.suppressalis is positively correlated with the density of Wolbachia.