Effects Of Temperature And Host Instar On Competition And Control Potential Of Two Parasitoids Of Bemisia Tabaci

Bemisia tabaci(Hemiptera Aleyrodidae)is one of the most important insect pest in vegetables,cotton and other agricultural and ornamental plants.At present,chemical control is still the main control measure of B.tabaci.However,extensive use of chemical pesticides has resulted in enhancement of chemical resistance of B.tabaci and increased threats to environment saftely.Therefore,it is urgent to utilize methods such as biological control that are environmental friendly and safe to human health.Eretmocerus and Encarsia are two important genus of whitefly parasitoids.Among them,Eretmocerus hayati and Encarsia formosa,are regarded as two key species in controlling B.tabaci.In this study,we tested the inter-and intra-specific competition and the impacts of temperature,host instar and host density on the competition outcomes and control potential to whitefly.The main results and conclusions were as follows:(1)The effect of temperature on competition and control potential of two parasitoids.We found Er.hayati prevailed in interspecific competition and could affect the outcome of En.formosa at 20℃,27℃ and 32℃.Meanwhile,Er.hayati showed strong intraspecific interference.Whereas the intraspecific interference was slight in En.formosa.At 20℃,the offspring of parasitoids and mortality of whiteflies were both less than those at two other temperature treatments.While the parasitoids showed high control potential at three temperature.(2)Effect of host instar on competition between two parasitoids.When female parasitoid individuls were introduced singly to clip cages with young nymphs or old nymphs of whitefly respectively,more offspring of Er.hayati were obtained from treatment of young nymphs of whitefly whereas for En.formosa the situation is on the contrary.However,in the competition test,the parasitoid Er.hayati is in a dominant position in final competition regardless the host instar.(3)The behavioral mechanism underlying the competition of the two parasitoids was studied.Through observation of host handling behaviors of these two wasp species,we found Er.hayati avoided some hosts that had been parasitized but En.formosa did not.This result implied that Er.hayati females were able to discriminate host status whereas En.formosa could not.Intrinsic competition results between the immature of two parasitiods were mainly depended on parasitoid species.Moreover,temperature and parasitation sequence impacted to some extent.In total,Er.hayati were in most cases dominant than En.formosa.(4)Evaluation of the competition of the two parasitoid species at greenhouse conditions was performed in 2017 and 2018.The results showed Er.hayati remained advantages in competition with En.formosa which were in consistent with laboratory experiments.