| Bemisia tabaci (Gennadius)(Hemiptera: Aleyrodidae) Middle East-Asia Minor1(MEAM1, alsocalled biotype B), a serious invasive pest in vegetables and broad-acre crops worldwide, has causedextremely serious economic losses during the last decades. The extensive use of chemical insecticides infood crops has resulted in the development of resistance against several insecticides, increasing threatsto the environment and human health. Thus, developing long-term integrated B. tabaci populationmanagement, with a strong natural enemy component, is a promising alternative. The classicalbiological control is a way to control invasive alien species by introducing specific natural enemiesfrom the original areas of the invasive pests. However, introducing single species might be difficult toachieve sustainable management of insect pests because of the lack of biodiversity. Therefore,introducing two or multiple species of natural enemy to establish a long-term management system hasbeen emphasized by numerous scientists. Unavoidably, when two or even more species with similarecological niche coexist in a biological control system, the competition for resource utilization mightoccur.Regarding the demand of establish sustainable biological control system of B. tabaci byintroducing multiple natural enemies, here we investigated the fitness differences and interspecificcompetitive interactions between Encarsia sophia (Girault&Dodd) and Eretmocerus hayati(Zolnerowich&Rose)(Hymenoptera: Aphelinidae), two prominent parasitoids of B. tabaci, and try tounderstand the concomitant mechanism affected by inter-and intraspecific interactions between thesetwo parasitoids. The main results and conclusions are as follows:1. The age-stage, two-sex life table were studied under laboratory condition (26°C±2°C,65±5%RH, and14L:10D regime) to evaluate the fitness difference between these two parasitoids. For En.sophia, the developmental time from egg to larva, from prepupa to pupa, and the longevity of adultswere6.4±0.1,6.5±0.1and16.0±1.3days, respectively; for Er. hayati, they were10.4±0.2,4.6±0.1and9.8±0.8days respectively. The oviposition period, fecundity, as well as maximum number ofoviposition per day for En. sophia and Er. hayati were18.5and15.1days,101.6and211.4eggs, as wellas22and54eggs, respectively. The population intrinsic rate of increase (r), finite rate of increase (λ),net reproduction rate (R-10)、mean generation time (T) of En. sophia were0.215d-1,1.2402d,57.49progeny/individual and18.82day, respectively; for Er. hayati, were0.214d-1,1.2383d-1,79.29progeny/individual and20.46day, respectively.2. The reproductive system structure and ovary developmental traits of these two parasitoids werestudied. Both parasitoid females’ reproductive system consisted of internal and external reproductiveorgans, including a pair of ovaries, six ovarioles, spermatheca, ovipositor and ovipositor sheath. Theovipositor of En. sophia is straight, has an apparently hard and sharply pointed upper valve, and appearswell-suited to penetrating a hard substrate, while that of Er. hayati is curved, thick-walled, but has ablunt and apparently flexible tip. These features correlate well with the mode of oviposition that En. sophia and Er. hayati ovipositing internally and externally respectively. Mature ova increased with theage of adult female when the available nutrition was enough.3. The host handling behaviors of these two parasitoids under various host habitats and in differentfemale introduction sequences were studied. Results showed that host handling behaviors of bothparasitoids, which included searching, accessing, oviposition, drilling by ovipositor, hostfeeding,preening, feeding on honey and standing still, showed particular phases and sequences. The differenthost types in the habitats showed more significant effect on En. sophia than Er. hayati. The femaleintroduction sequences did not affect the host handling behaviors of both parasitoids significantly.However, host acceptance rates of two parasitoids when time interval is0h were higher than when timeinterval is48h. The acceptance rates, rejection rates and host-feeding rates of En. sophia on heathy hostsand parasitized hosts (conspecific or heterospecific) were not significantly different. However,acceptance rate of Er. hayati on healthy hosts was significant higher than on conspecific orheterospecific hosts.4. Results of intrinsic competition between the immature of the two parasitoids indicated that thecompetition outcome varied with the introduction sequence and time intervals of different female adults.When En. sophia was introduced first, it outcompeted the competition regardless of the time intervals (0,24,48h). When Er. hayati was introduced first, it prevailed at the time interval72h. This result might beexplained by shorter development time of egg of En. sophia when compared to Er. hayati.5. To understand the effect of host resources availablity on interspecific interaction of twoparasitoids and host suppression, the inter-and intraspecific competitive interactions between En.sophia and Er. hayati under different host densities and host instars were evaluated. For En. sophia,while the host density was low, intraspecific interference was stronger than interspecific interference.What’s more, the interspecific interference increased with host densities. For Er. hayati, the interspecificinterference were always stronger than intraspecific interference, and decreased with increasing hostdensity. Host instars also affected the outcome of interspecific competition of these two parasitoids. Er.hayati won the competition while provided with young host instars (first and second instar nymphs),and this advantage decreased while provided with older host instars. |
PDF Full Text Request