| We mainly conducted six experiments focusing on a naturally occurring parasitoid in China, Eretmocerus hayati (Hymenoptera:Aphelinidae), in order to overall evaluate the biological control potential, which has extensively existed in the fields of northwest China as a predominant solitary whitefly parasitoid.Firstly, we identified two natural occurring Eretmocerus parasitoids in China by CO I sequence analysis and crossing test; Secondly, To explore the effects of various sugar type and concentrations on parasitoid fitness, we compared5%,10%and20%(w/v) solutions of six different sugar resources (glucose, fructose, sucrose, trehalose, melezitose and honey) on the longevity of a natural occurring Eretmocerus hayati; Thirdly, we explored the host instar suitability of this species on two invasive whiteflies, Bemisia tabaci MEAM1and MED; Fourthly, we studied Ovigeny Index (OI) of Eretmocerus hayati and investigated the effects of the combinations of host availability levels (unavailable, daily available for6h and daily available for24h) and non-host foods (water and honey) on life history traits and the risks of egg/time limitation; Fifthly, we investigated the life table parameters of this speices reared on Bemisia tabaci during different rearing temperatures and oviposition temperatures; Lastly, in order to explore how extreme temperatures does affect the life history traits of the different stage of parasitoids, we compared the effects of different frequencies of heat wave on the lifetime fitness of Eretmocerus hayati, enduring on different development stages. Mainly results were followed below:1Identification of two natural occurring Eretmocerus parasitoids by CO I sequence analysis and crossing testEretmocerus parasitoids are of a parasitoid genus with small size and tiny difference, which makes them hard to be identified quickly and accurately by traditional morphological identification methods. The mitochondrial cytochrome c oxidase subunit I (CO I) genes analysis and crossing test between two similar populations were conducted for identifying two Eretmocerus species or populations. The CO I genes of4Eretmocerus species or populations(Eretmocerus hayati, Eretmocerus funihashii, Eretmocerus sp. XJ, Eretmocerus sp. LF) were amplified using universal primers and sequenced. The phylogenetic trees were respectively established by Maximum parsimony (MP) and Maximum likelihood (ML) method. The intra-and inter-species genetic distances were calculated with MEGA5.0software using the Kimura2-Parameter model. Furthermore, a crossing test between two similar populations was conducted to confirm the reproductive compatible. The results indicated that Er. furuhashii and Er. sp. LF were assembled into the same branch. Meanwhile, the intra-specific genetic distances of two populations were0.0029and0.0173, but the inter-specific genetic distance of them was0.011. Similarly, Er. hayati and Er. sp. XJ were assembled into the same branch. Meanwhile, the intra-specific genetic distances of two populations were0.0023and0.000, but the inter-specific genetic distance of them was0.024. Furthermore, the results of crossing test between Er. hayati and Er. sp. XJ suggested that there was no significant reproductive incompatible. That is to say, they were same species. The combination CO I sequence analysis with crossing test for identifying similarly small insect species not only improved the accuracy of identification, but also provided an effective complement to CO I sequence analysis. This research could shade a light on how to identify of other tiny insects to some extent.2Effect of Six Carbohydrate Sources on the Longevity of a Whitefly Parasitoid Eretmocerus hayati (Hymenoptera:Aphelinidae)Parasitoid adults usually acquire carbohydrates by feeding on floral nectar and honeydew which provides them with energy and has an effect of prolonging their life span. The concentration and quantity of saccharides in nectar and honeydew are variable by plant species or phytophagous insects. To explore the effects of various sugar type and concentrations on parasitoid fitness, we compared5%,10%and20%(w/v) solutions of six different sugar resources (glucose, fructose, sucrose, trehalose, melezitose and honey) on the longevity of a natural occurring Eretmocerus hayati, a predominant larval parasitoid of the whitefly Bemisia tabaci in China. All female and most male parasitoids had significantly prolonged life spans by each sugar diets. Female parasitoids feeding on10%glucose and10%honey increased longevity, respective up to6.2-and5.9-folds longer than water;5%honey and10%fructose had the greatest effects on male longevity, up to3.5-and3.3-folds. All six sugar diets, no matter which concentration, significant changed the survival curves. Glucose and honey were optimal sugar diets for this wasp, and10%was the optimal concentration. Our results could provide an insight into the nutritional requirements of Er. hayati under laboratory conditions. Such information can be a basis to improve the longevity of this biological control agent by sugar feeding during the indoor mass-rearing process.3Host instar suitability of naturally occurring Eretmocerus hayati on two invasive whiteflies in ChinaHost instar suitability of a parasitoid is critical to ensure bio-control efficacy and mitigate host damages. Studies were conducted to assess parasitizing and feeding behaviors of a natural occurring parasitoid, Eretmocerus hayati, on different instar nymphs of two invasive whiteflies, Bemisia tabaci (Gennadius) MEAM1and MED in China. Our results showed that Er. hayati parasitized and fed on all nymphal hosts of two whiteflies, and preferred to parasitize1st,2nd and3rd instar hosts of B. tabaci MEAM1and2nd instar hosts of B. tabaci MED. The ovipostions on1st,2nd,3rd and4th instar hosts of B. tabaci MED were1.64,1.23,1.60and1.13folds larger than those on B. tabaci MEAM1, respectively. Similarly, parasitoids preferred to feed on earlier instar hosts of the two species. The preimaginal development times of parasitoids on two hosts were the longest in1st instar hosts, intermediate on2nd and3rd instars, and shortest on4th instars. Meanwhile, the immature development time on each instar nymphal hosts of B. tabaci MED were slight shorter than MEAM1. The highest parasitoid survivorships on both whiteflies were on4th instars, and the lowest were on1st instars. The sex ratios of offspring remained stable at0.5. We suggested that Er. hayati could be more suitable biological control agent for B. tabaci MED. Our results could provide guidance for indoor mass-rearing of Eretmocerus spp. for inundative release in the field, accelerating IPM programs against B. tabaci in China.4Income resources and reproductive opportunity change life history traits and the risks of egg/time limitation in a synovigenic parasitoidSynovigenic parasitoids emerging with no or only a few mature oocytes could not only utilize capital resources, but also need to acquire income resources (non-host and host food). Income resources stochastic existing in nature can either contribute nutrition to mature egg as a food resource and/or create unpredictability in realized reproductive opportunities for synovigenic parasitoids. Therefore, we hypothesized they could affect the life history traits and the risks of egg/time limitation in synovigenic parasitoid. Here we explored Ovigeny Index (OI) of Eretmocerus hayati, a predominant parasitoid on Bemisia tabaci, and investigated the effects of the combinations of host availability levels (unavailable, daily available for6h and daily available for24h) and non-host foods (water and honey) on life history traits and the risks of egg/time limitation. Host availability levels represented the various reproductive opportunities. Our results firstly showed that the Ovigeny Index (OI) value of Er. hayati was0.28, which suggested it was a typical synovigenic wasp. Secondly, both host availability level and non-food type had significantly different effect on the life history traits of this parasitoid, but host food was the optimal income resource and host feeding was the major tool for acquiing additional nutrients. Thirdly, the risks of egg/time limitation were encountered by all wasps and varied with host availability levels. In summary, our results confirmed that the income resource and reproductive oppoitunity played a central role in shaping the life history and the risks of egg/time limitation of a synovigenic parasitoid.5Changing biological control efficacy of an aphelinidae parasitoid by switching rearing and oviposition temperatures:a new insight into mass-rearing of parasitic natural enemiesDevelopment, survival, fecundity and age-specific life-table parameters of a native strain of the parasitoid Eretmocerus hayati Zolnerowich&Rose (Hymenoptera: Aphelinidae) reared on Bemisia tabaci cryptic species MEAM1were examined at different rearing and oviposition temperatures (26+26℃,30+30℃,34+34℃) and different rearing but identical oviposition temperatures (30+26℃,34+26℃). Under both of temperature regimes, immature development times and life history traits (fecundity, host feeding, longevity, reproductive efficacy and host suppression efficacy) were shortened/decreased when the temperature increased from26℃to34℃. The highest intrinsic (r) and finite (λ) rate of increase were found at the rearing/oviposition regimes of30+30℃and30+26℃. All these parameters increased significantly with the decreasing temperatures during the same rearing but different oviposition temperatures.r Our results showed that accelerating the immature developmental rate and increasing the adult life history traits by switching of the temperatures across immature stage (rearing temperature) and adult stage (oviposition temperature) can obtain better reproductive efficacy and host suppression efficacy during a period.6The biological control potential of Eretmocerus hayati affected by heat wavesHeat waves-extended periods of abnormally hot weather-are predicted to increase in severity and frequency under climate change. The severity of heat waves should impact communities and food webs through effects on perfonnance of individual species and through changes in the strength of interactions between them. This study tested the effects of severity of simulated heat waves, with daily maxima of42℃, on a tritrophic food web consisting of cotton plants, whitefly (Bemisia (abaci MEAM1) and parasitoid (Eretmocerus hayati).We focused on how immature ontogeny, life history traits, the reproductive efficacy, biological control efficacy and population traits of Er. hayati did affect by heat waves. The results showed that when single developmental stage met heat waves, lower frequency of heat wave had no significant affect on immature development, life history traits and population triats of parasitoids. However, when higher frequency of heat waves was encountered, the life history traits and population traits of parasitoids when larval stage or pupa stage experienced heat waves were significant changed. Parasitoids may have experienced delayed and prolonged immature development, decreased longevity, reduced fecundity and host feeding. Furthermore, if two or three developmental stages of parasitoids faced higher frequencies of heat waves, those life history traits and population traits were significantly affected. In this experiment, we observed effects of heat waves on absolute abundance of individual species. Meanwhile, at the community level, we saw evidence of effects of heat waves on population dynamics. That is to say, heat waves not only affected the ontogeny of parasitoid, but also deteriorated the reproductive and biological control efficacy and poplation dynamics. Temperature determines the rates of metabolic processes, which in turn ultimately determmes the rates of biological processes ranging from growth and development to feeding and dispersal rates. This, in turn, may determine levels of connectance in communities. Community-level effects of perturbation from global phenomena such as heat waves are more likely to result from effects on physiology and behavior that govern the interaction between species than from the effects on strictly internal processes such as development and growth. Hence, the experiments that focus on plant-herbivores insect-parasitoid. such as outcomes of parasitoid foraging, or the bottom-up effects of plant solute concentration under thermal stress, might be a good place to explain the effects of global climate change on community relationships. |
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