Mechanisms For Host-feeding And Parasitism Capacity Of The Whitefly Parasitoid Encarsia Sophia Improved By Starving For A Certain Period Of Time

Many species of insect parasitoids, especially most species of the parasiticHymenoptera, not only oviposit on their hosts, but also feed on them (called hostfeeding). The parasitoid species with host-feeding habits have been considered aspromising biological control agents. Recent studies indicated that some host-feedingparasitoid species starved for a certain period of time can more effectively killwhiteflies through host feeding and parasitism than can unstarved parasitoids. In orderto elucidate the underlying mechanisms, in this study, the autoparasitoid Encarsiasophia, a typical host-feeding parasitoid, was selected as test species. We investigatedthe effect of food-deprivation for a certain period of time on their host-feeding andparasitism behaviors, and the impact of number of host fed and honey solution onnumber of eggs loaded, vitellin content and longevity. The important findings asfollowed.1.When Trialeurodes vaporariorum and bemisia tabaci were simultaneouslyoffered on a same tomato leaf, E. sophia that was deprived food for6h and20ï¼…honey solution offered for6h killed more whitefly nymphs through host feeding andparasitism than those without food deprivation.2. All of the host-feeding and parasitic functional response for starved andunstaved E. sophia exhibited the Holling type II models. The mean number ofwhitefly nymphs killed by host feeding and parasitism in both treatments increased ashost density increased. The handling time of unstarved parasitoids (for host feeding:0.2093d; for parasitism:0.2627d) on a single host was nearly two times longer thanthe handling time of starved parasitoids (for host feeding:0.1082d; for parasitism:0.1376d). The theoretical maximum number of hosts fed on and parasitized bystarved parasitoids, given by the asymptote (1/Th) of the functional response curve,was respectively9.2421and7.2674hosts per day per female, also nearly two timesgreater than the number of hosts killed by unstarved parasitoids (for host feeding:4.7778hosts; for parasitism:3.8066hosts). 3. The starved E. sophia killed significantly more whiteflies through hostfeeding and parasitism than did unstarved parasitoids. The time spent finding the firsthost used for host feeding and parasitism in unstarved females was approximately5.7and2.8times respectively longer than the time spent by starved females. Generally,unstarved parasitoids exhibited significantly longer handling times (1151.9s) to kill asingle host through parasitism than starved parasitoids (271.9s). These results ofbehavioral observations and the functional response test, confirm that the starvedparasitoids can use a shorter time to find and handle their hosts, thereby killing morepests using the saved time.4. The nutrients obtained from host-feeding on whitefly nymphs couldpromote vitellin generation in E. sophia, and increase their egg production. There wasno significant difference in longevity among those E. sohpia females feeding ondifferent numbers of whitefly nymphs. However, the nutrients obtained from feedingon honey solution could significantly prolong their longevity.There were differentdynamic changes in III grade eggs (mature eggs) between mated and unmated femaleparasitoids after feeding on whitefly nymphs and honey solution. The mature eggsmated female parasitoids increased after feeding on whitefly nymphs and honeysolution. However, after emergence12h, the number of mature eggs began to reduce.There was no significant difference in number of III grade eggs among unmatedEncarsia sophia females feeding on1-3whitefly nymphs. However, there was asignificant tendency of mature eggs increase in unmated females after feeding onhoney solution.Generally, compared with unstarved E. sophia females, the starved females tooka shorter time to find hosts used for host feeding and parasitism after releasing.Meanwhile, the starved females took a shorter time to finish host feeding andparasitism on hosts. In addition, the nutrients obtained from host feeding on whiteflynymphs could increase vitellin generation and egg production. Therefor, thehost-feeding and parasitism capacity of the whitefly parasitoid E. sophia can beimproved by starving for a certain period of time.