| The host-feeding parasitoid female can feed on the host tissue and/or hemolymph, and eventually killthe host or decrease the host suitability. Synovigenic parasitoid emerges with no or only few matureeggs in the ovaries, thus they have to feed on host food and/or non-host food to acquire nutrient for eggmaturation and body maintenance during adult stage. The "ovigeny index" quantifies the degree ofsynovigeny, measured as initial egg load (fully mature eggs) divided by potential lifetime fecundity,with1denoting strict proovigeny and0denoting strong synovigeny. Few attentions had been paid onthe behavior pattern (such as parasitism and host feeding) and potential (directly host killing) of hostfeeding parasitoids. Meanwhile, host feeding parasitoid usually faced the trade-off between currentreproduction and future reproduction when host was supplied. Neochrysocharis formosa (Westwood)(Hymenoptera: Eulophidae) is one of the most dominant natural enemies of agromyzid leafminer pests,which are major pests in many parts of the world. This wasp is a typical synovigenic parasitoid, not onlyparasitizing host larvae, but also feeding on host haemolymph to obtain nutrients. Hence, present studyfocusing on the behavior pattern and potential host suppression ability of the host feeding parasitoid, N.formosa against agromyzide leafminer, would have significantly scientific values and applicationpotentials. In this study, we firstly used two-sex life table to evaluate the pest control potential of N.formosa and Diglyphus isaea, another predominant parasitoid of agromyzid leafminer pests in China;secondly, we studied the host handling behaviors and host feeding mode of the two parasitoids femaleon the third instar larva of Liriomyza sativae Blanchard; thirdly, we explored the effects of nutritionalsupplements on host-feeding ability and potential host suppression ability, including the effects ofadditional non-host food on the female life history traits, the preference of host feeding or oviposition;fourthly, we compared the effects of additional non-host food on trade-off of feeding vs. oviposition intwo synovigenic parasitoids. The main results and conclusions are summarized as follows:1. The evaluation of the suppression potential of two host-feeding parasitoids against leafminer usingtwo-sex life table methodsThe destructive host-feeding parasitoids not only lay egg to parasitize the host but also direct feed onhost or kill host. In order to better understand the two species’s potential biological control agent, weconstructed the age-specific and two-sex life tables of N. formosa and D. isaea under the conditions of25±1℃,75%±5%relative humidity (RH) and a photoperiod regime of14L:10D in the laboratory. Theresults showed that there were no significant differences in female larval developmental time andlongevity of males between two wasps, while significant differences were found in other traits (such aspupal stage, immature developmental time, female longevity, host mortality by laying egg, hostmortality by host feeding or host killing). Meanwhile, the majority statistics were bigger in D. isaeathan in N. formosa. Our result showed both of two parasitoids have quite strong host suppression ability,while N. formosa would be suit to inundative release and D. isaea be suit to inoculative release. Ourconclusion could provide an insight in how to use and release the two species for controlling theleafminer pests in the field. 2. Host-handling behavior pattern and host mortality mode of N. formosaThe destructive host-feeding parasitoids either kill the host by reproductive host-killing (parasitism) ornon-reproductive host-killing (host feeding and host killing). But there were rare studies focusing on thehost-handing process and the factors affecting the behavioral decisions between oviposition andhost-feeding behavior. Host-handling behavior can be affected by the life history and the intrinsicphysiological levels and external factors. In present studying, the host handling behavior of the femaleN. formosa (Westwood), which have host-feeding and oviposition experience, on the three instar larvaeLiriomyza sativae Blanchard in two hours was systemic observed by anatomical lens. The host-handlingbehavior was divided into the egg laying and host feeding behavior, and the parasitoids were classifiedinto two groups, new emergence and four-day old. Furthermore, we quantitated and compared the eachbehavior’s total time, the time of each single behavior, the frequency of each behavior and so on. Theresults showed that the host handling behavior of females included searching, probing, hackling,ovipositor insertion, host feeding and resting; the parasitoid-induced mortality included host feeding,egg-laying and host sting, but the previous step of this three kinds was ovipositor insertion. Thebehavior type what parasitoids have would be chosen before the behavior was established. In view ofthe "purporting" of the female, host-sting without feeding and oviposition can be unsuccessfulegg-laying behavior.The host-handing efficiency of four-day old female was significantly higher than those of the newemergence one. The average amount of parasitism, host-feeding events, host stinging events and hostmortality of two parasitoids were9.0±0.75vs3.3±0.46,1.4±0.09vs1.3±0.12,2.6±0.48vs1.6±0.26,12.4±0.56vs6.2±0.54in two hours observation, respectively. We supposed that the host-feedingbehavior was non-concurrent, but in rich-egg load situation, the female can parasitize and feed on thesame host, but which generally occurred at different time.Otherwise, the females of two wasps had ability to identify host. The host rejection rate of newemergence female encountering the parasitizing hosts was26.7%, but four-day-old females did notreject any more.3. Effects of additional non-host food on the adult life history traits and shift preference of feeding vs.oviposition of N. formosaThe host-feeding parasitic wasps can also feed on non-host foods, including honey, various sugars,honeydew and so on. We studied the effects of host food and non-host foods on female life history traitsof N. formosa, for example longevity, fecundity, parasitoid-induced mortality and so on. Furthermore,we analyzed the effects of adding non-host food on trade-off of feeding vs. oviposition. The resultsshowed that:1) Relative to the water solely treatment, host food significant increased longevity,fecundity, the number of host-only-stinging and total host mortality;2) Addition non-host food (10%honey solution) increased average daily fecundity, decreased average daily host feeding and preferred tooviposition in shifting preference between oviposition vs. host-feeding significantly, but did not changethe average daily number of host-only-stinging and host mortality. Addition non-host food enhancedfecundity, the number of host-only-stinging and host mortality through prolonging the longevity, but increased the value of host-feeding meals to the fecundity, the number of host-only-stinging andlongevity significantly through decreasing the host feeding events. This paper mainly discussed thenutrition utilization strategies of the host-feeding parasitoid and effects of additional non-host food onthe host-feeding parasitoids, especially on the biological control applications.4. Effects of additional non-host food on trade-off of feeding vs. oviposition of the two synovigenicparasitoids, N. formosa and D. isaeaThe host-feeding parasitoid female either killed the host through feeding host or obtained nutrition forreproduction and body maintenance. The trade-off of feeding vs. oviposition was closely related to theoogenesis. We took two different synovigenic parasitoids to observe host-feeding and egg-layingbehaviors of the pre-emergence female under host food and non-host food conditions.The results showed that:1) Under host food and non-host food conditions, the three types ofparasitoid-induced mortalities of N. formosa were different significantly, but of which the egg-layingwas the largest. However, when host food was supplied, total amount of host-feeding events and numberof host-only-stinging were not significant difference, significant difference resulted from addingnon-host food; In the two treatments, the differences among the three types of parasitoid-inducedmortality of Diglyphus isaea were different significantly, followed as host-feedingevent<fecundity<number of host-only-stinging.2) The effect of additional non-host food-glucose ondifferent lethal factor relative to the host food treatment, the host feeding and fecundity decreasedsignificantly; the number of host-only-stinging increased significantly and the host mortality did notchange significantly in N. formosa; Otherwise, for D. isaea, the host-feeding events, fecundity, numberof host-only-stinging and host mortality decreased significantly.3) From the parasitoid-inducedmortality between two species, the host-feeding events, fecundity and host mortality for N. formosawere higher significantly than D. isaea under the two treatments. However, under host food treatment,the number of host-only-stinging for N. formosa were lower than D. isaea, and under non-host foodtreatment, the number of host-only-stinging for N. formosa were significantly higher than D. isaea. |
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