Insect Heliothis Virescens Ascovirusmediated Feeding Selection Behavior Of Spodoptera Litura Larva

The infection of pathogenic microorganisms would lead to the changes on the development and behavior of host insects.Ascoviruses are insect viruses that mainly attack noctuic larva and are potential to develop into biocontrol agents.To data,the researches on the ascoviruses were mainly focused on the basic levels.Little was known on the regulating or the interaction between herbivorous insects and host plants that was modulated by ascoviruses.Therefore,Heliothis virescens ascovirus 3h,Spodoptera litura larva,and pepper were used as research objects in this study.The feeding selection and olfactory selection behavior of S.litura larva on pepper leaves under healthy and larva feeding treatment were observed,and then observed the olfactory selection behavior of healthy and infected larva on pepper leaves treatment with healthy larva and infected larva;furthermore,the olfactory selection behavior of healthy or Hv AV-3h infected larva were observed by each simulated feeding treatment.Gas chromatography-mass spectrometry(GC-MS)was used to identify and analyze the components and release amounts of volatile substances in pepper leaves under different treatment.The interference pattern of larva induced plant volatiles caused by S.litura infected by Hv AV-3h on host selection behavior of healthy larva was clarified.The main findings are as follows:(1)The preference of healthy S.litura larva on the feeding and olfactory selection behavior of pepper leaves under healthy control and insect feeding treatment was clarified.Healthy S.litura larva have a significant preference for pepper leaves treated with insect feeding for 24 h and 48 h.;The olfactory selection results showed that healthy larva had a preference for treatment with insect feeding for 3 hours,and then the selection rate increased,reaching the highest value after 12 hours,and then tended to be flat.The experiment of olfactory selection of healthy larva was carried out by simulating insect feeding process with mechanical damage and smear regurgitant of larva.The results showed that both mechanical damage treatment and regurgitan treatment attracted S.litura larva in different degrees,and the choice of “mechanical damage + regurgitant treatment” was significantly higher than that of mechanical damage treatment and regurgitant treatment.(2)Healthy S.litura prefers pepper leaves fed by infected insects(pepper leaves treated with Hv AV-3h infected larva)than pepper leaves fed by healthy larva.S.litura larva and healthy S.litura larva were infected with three near-origin Heliothis virescens ascovirus strains as insect sources,fed pepper leaves respectively and then tested healthy S.litura with different pepper leaves(4 treatments).On the olfactory selection behavior of larva among the four treatments,it was found that pepper leaves infected with Hv AV-3h were more attractive to S.litura.However,there was no significant preference for pepper leaves treated with regurgitant of Hv AV-3h larva,preferring "mechanical damage + regurgitant of infected insects",and there was no significant difference between “mechanical damage+ regurgitant of healthy insects” and “mechanical damage + regurgitant of infected insects”.(3)Volatiles from pepper leaves under different treatments were collected,identified and quantitatively analyzed.The results showed that in the comparative analysis of volatiles among the healthy treatment,the insect feeding treatment and the infected Hv AV-3h larva feeding treatment,the total amount of volatiles released from pepper leaves treated by healthy S.litura insects was significantly higher than that of pepper leaves treated by infected insects and healthy controls,but the species of volatiles in pepper leaves treated with infected Hv AV-3h insect feeding were more abundant than those treated with healthy and healthy larva feeding.Compared with healthy treatment of pepper leaves,the release of green leaf,aldehydes and terpenes volatiles in leaf volatiles under insect feeding treatment increased significantly,while alkanes were lower.In the comparative analysis of volatiles between healthy control and mechanical damage treatment,regurgitant of healthy larva and Hv AV-3h infected larva,the total amount of volatiles released from pepper leaves and the types of volatiles in the mechanical damage treatment were higher than the other three treatments,the regurgitant treatment of healthy larva and Hv AV-3h infected larva showed little difference in the amount and quantity of volatiles released.There was no significant difference in terpenoids volatiles among the treatments,and green leaf and ester volatiles were significantly different in the mechanical damage treatment was higher than the other three treatments,the aldehyde volatiles of healthy larva regurgitant treatment and Hv AV-3h infected larva regurgitant treatment were significantly lower than those of healthy control and mechanical damage treatment,However,the alkanes in mechanical damage treatment,regurgitant of healthy larva and Hv AV-3h infected larva treatment were significantly higher than those under healthy treatment.(4)The olfactory selection behavior of S.litura larva detection with the prepare mixed solutions prepared from commercial obtained compound standards(20 standards).The results showed that the volatile mixture treated with Hv AV-3h infected larva feeding had the highest attraction to healthy S.litura larva,followed by the volatile mixture treated with healthy larva feeding,both of which were significantly higher than those healthy pepper.The standard test of different kinds of mixed solutions showed that the selection of terpenes and ketones by S.litura larva under the treatment of healthy and Hv AV-3h infected insects was significantly higher than that under the healthy treatment,but there was no significant difference in the selection of all kinds under the treatment of healthy and Hv AV-3h infected larva.According to the release amount of each single product in the volatiles of pepper leaves under the treatment of healthy and Hv AV-3h infected larva feeding,single standard samples with different concentrations were prepared to observe the olfactory selection behavior of healthy S.litura larva.The results showed,the standard of 2-hexenal under healthy insect feeding treatment significantly attracted S.litura larva compared with healthy and Hv AV-3h infected larva feeding treatments,cis-Jasmone,and geranylacetone standard under the Hv AV-3h infested larva feeding treatment significantly attracted S.litura larva compared with the healthy treatment and healthy insect feeding treatment,while the standard of homosalate under the Hv AV-3h infested larva feeding treatment attracted larva is significantly lower than these two treatments.The volatiles such as trans-2-hexenal-1-alcohol,trans-2-trans-4-Octadienal,1,2-Dimethoxybenzene,methyl salicylate,(2E,6E)-nona-2,6-dienal and β-ionone were more attractive to S.litura larva under the treatment of healthy insect feeding and Hv AV-3h infected larva feeding than those under healthy control,while β-Cyclocitral,(2E,4E)-Deca-2,4-dienal and 4-(2-Butyl)phenol is more attractive to S.litura under healthy control.Idole,benzaldehyde,guaiacol,(Z)-β-ocimene,3-Ethylbenzaldehyde,phytol and nonanal had no obvious preference difference among the three treatments.