Effects Of Interactive Infesting Chinese Kale With Plutella Xylostella And Bemisia Tabaci On Biology Of Encarsia Formosa And Cotesia Plutellae

Bemisia tabaci（Gennadius）and Plutella xylostella（Linnaeus）are two serious cosmopolitan pests.Encarsia formosa and Cotesia plutellae are two dominant endoparasites of B.tabaci and P.xylostella,respectively.During agricultural production practice,the whitefly and diamondback moth often co-occur and attack the same plant.In order to develop the joint application technology of a variety of natural enemies to control various pests,we use specific age-stage two-sex lifetable technique to research the biological characteristics of natural enemies E.formosa and C.plutellae when P.xylostella and B.tabaci simultaneously or sequentially feed on Chinese kale plant.The main results as follows:1.When B.tabaci and P.xylostella simultaneously infested Chinese kale plant,the pre-adult developmental time and the total pre-oviposition duration of E.formosa were extended,and the adult duration and fecundity decreased.The age-stage-specific curves(s_xj),the age-specific fecundity（m_x）,age-specific net maternity（l_xm_x）and cumulative age-specific net maternity（Cumu-l_xm_x）,the finite rate of increase（λ）,the intrinsic rate of increase（r）and the net reproductive rate（R₀）of E.formosa significantly decreased.In addition,the mean predation rate to B.tabaci second instar nymphs and the net predation rate（C₀）of E.formosa obviously decreased.Sequential infestation of two pests had no effects on life history,population parameters and predation parameters of E.formosa.2.When the whitefly and the diamondback moth co-fed on host plant,the larval duration,pupa duration,adult duration,longevity,the mean generation time（T）,the finite rate of increase（λ）,intrinsic rate of increase（r）and pupa weight of C.plutellae had no significant differences,but the fecundity（F）was decreased significantly.Both the fecundity（F）and the net reproductive rate（R₀）of C.plutellae after sequentially infestation by P.xylostella and B.tabaci were decreased significantly,whereas the different developmental stages,lifespan,pupa weight and other population parameters had no significant changes.In general,simultaneous infestation of the whitefly and the diamondback moth resulted in longer developmental duration,lower population growth of E.formosa,and the reduced fecundity of C.plutellae.which may lead to the decrease of the biocontrol effects of the natural enemies.On the other hand,the effects on two natural enemies were asymmetric when P.xylostella and B.tabaci damaged the host plant in different order.The pre-feeding by whiteflies caused the reduction of control effect of C.plutellae.In contrast,the pre-feeding by the diamondback moth had no significant effect on E.formosa.