Effects Of Intestinal Microorganisms On The Infection Of Different Baculoviruses On Spodoptera Exigua Larvae

Applications of baculovirus as insect pesticides have been limited by it’s low speed of killing and narrow insecticidal spectrum.Host changes,for example,microorganisms in vivo,provide new research directions in improving virus virulence.It is reported that intestinal microorganisms take part in assisting digestion,regulating reproductive activities and participating in immune response of host insects.Meanwhie,RNAi plays an active role in anti-virus immunity in some insects.In oeder to find out their links and whether such links can improve baculovirus insecticidal efficacy,this study examined the intestinal microbial composition of Spodoptera exigua larvae treated with virus,tested the virus virulence of different viruses to the larvae after antibiotic clearance,detected the expression of immune-related genes in the midgut tissues of the larvae after different viral treatments,and determined the changes of body weight and food intakes of both S.exigua larvae and Spodoptera litura larvae after different viral infections.Here are the results:(1)High throughput sequencing showed that after 12 hours of treatment with AcMNPV,the number of bacterial species,diversity and homogeneity of bacterial community in intestinal tract of 4th instar larvae of S.exigua are higher than those of normal larvae with a opposite trend of fungal community.(2)When cleared up intestinal microorganisms by antibiotics,the LC50 of SeMNPV,AcMNPV and SpltMNPV on the 3rd instar larvae decreased in different degrees,meaning that microorganisms may play active roles in the immune and antiviral process of S.exigua.(3)RT-qPCR showed that after treatment with SeMNPV,AcMNPV and SpltMNPV,the expression of Dicer-2,the key gene of RNAi process,increased at different degrees.Meanwhile,the expression treated with CpGV was similar to that of healthy larvae.The first 3 viruses might induce RNAi in the larvae.(4)The weight of 4th instar larvae of S.exigua treated with SeMNPV was the highest after 36h,48h,60h,72h and 84h,and the difference was significant.For the 4th instar larvae of S.litura,the food intakes of SpltMNPV group at 48h and 84h were significantly higher than that of the control,the body weight of the larvae treated with SpltMNPV was significantly higher than that of the control at 72h and 84h.Viruses may stimulate insects to increase their food intake to obtain the energy needed for immune activity against infection.