Changes Of Host Preference In Spodoptera Litura And The Role Of Plant Volatiles In Its Host Selection

Spodoptera litura Fabricius is a Lepidoptera polyphagous pest that widely distributed around the world and causes great harm to agricultural production.The host selection characteristics of S.litura have important effects on its occurrence pattern,regional population dynamics and damage.A large number of studies had shown that the host preference of herbivorous Lepidoptera insects was also influenced by many factors such as the feeding plants and their experiences on the basis of genetic determination.However,most of the existing studies only carried out a short-term trial(the same generation or their offspring),did not evaluate the impact of multi-generation feeding,and there were few studies on the influence of different plant growth periods on host selection of S.litura.Existing studies had shown that some plant volatiles could affect the host selection of S.litura,but most of them only studied the effects of a single component,and few studies focused on the compound effect of plant volatiles.In this paper,we studied the host selection changes of larvae and adults of S.litura after feeding for four generations of same host plants,and evaluated the impact of multi-generation S.litura feeding host experiences on host selection.Using different growth stages of cabbage and soybeans to explore the host selection of S.litura to different plant growth stages and effects of plant growth stages on host selection of S.litura in the presence of various host plants.Using the four-arm olfactometer and electroantennogram technology to explore the effect of the cabbage volatiles on the host selection of S.litura.The main results are as follows:1.Multigenerational feeding experience of host plants could change the feeding preference of S.litura larvae,but there was no significant effect on the oviposition preference of adults of S.litura.Feeding four generations with different host plants,S.litura larvae produced a greater change in the order of feeding preference for the four host plants,but the changes were not consistent.After feeding multiple generations with cabbages or soybeans,the offspring larvae had an increased preference for the host,while feeding on non-crop plants Alternanthera philoxeroides or Trifolium repens Linn,S.litura did not show changes in preference for the host.Adult S.litura that fed the same plant for several generations showed no significant changes in the order of oviposition preference of four species.2.S.litura had different preferences for different growth periods of plants.The 3rd instar larvae of S.litura prefered to eat seedling cabbage while 5th instar larvae prefered the rosette Cabbage,both prefered the soybeans during flower bud differentiation,adults prefered to oviposit on the knot cabbage and pod bearing soybean.In the presence of multiple host environments,plant growth period affected the host selection of S.litura larvae,The 3rd insatar larvae of S.litura had no significant feeding preferences for the four host plants:seedling cabbage,flower bud differentiation period soybean,adult-plant stage T.repens and A.philoxeroides.The preference of S.litura adults for different host plants did not be changed by the different growth periods of plants.3.The electroantennogram of S.litura increased with the concentration of plant volatiles,and had strong electrophysiological responses to trans-2-hexenal,nonanal,benzaldehyde and linalool in cabbage,while decanol,farnesene,myrcene,carvone,caryophyllene,benzyl alcohol could only produce significant electrophysiological responses to S.litura at higher concentrations.The compound effects of volatile substances were not a simple superposition.100 mg/ml of linalool with repellent effect against S.litura mixed with benzaldehyde which had attractive effect,the electrophysiological response of male adult S.litura was significantly improved.The combination of plant volatiles with the same behavioral responses to S.litura did not necessarily result in a stronger electrophysiological response to S.litura.The combination of trans-2-hexenal and linalool with repellent effects against S.litura at 100 mg/ml significantly improved the electrophysiological response of S.litura.However,the electrophysiological response of S.litura did not increase significantly after the combination of nonanal and benzaldehyde which had an attraction effect on S.litura at concentrations of 100 mg/ml.The physiological response did not increase significantly.The concentration of components in the complex volatiles also affects the electrophysiological response to S.litura.The combination of 100 mg/ml benzaldehyde and 10 mg/ml linalool had weaker electrophysiological responses to S.litura than compounds of the same concentration at 100 mg/ml.In addition,the electrophysiological responses of male and female insects to compound volatiles were quite different.