Predation, Prey Preference And Life Table Of Amblyseius Orientalis On Bemisia Tabaci And Tetranychus Cinnabarinus

The whitefly, Bemisia tabaci(Gennadius)(Hemiptera: Aleyrodidae), is one of the most serious agricultural pests in worldwide. Biological control has become a major alternative to chemical control for a long time, and keeps catching increasing attentions. Amblyseius orientalis(Ehara)(Acari: Phytoseiidae) is a native predatory mite species widely distributed in China. It used to be considered as a specialist predator of spider mites. However, recent studies showed it also preys on other small arthropod pests, such as Bemisia tabaci(Gennadius)(Hemiptera: Aleyrodidae). But previous field experiments showed its population failed to increase when whitefly was its only prey in greenhouse. Under natural circumstances, whiteflies often occur together with Tetranychus spp., such as Tetranychus cinnabarinus(Boisd.)(Acari: Tetranychidae). To investigate predation and population dynamics of A. orientalis when both these two types of prey are available, three sets of experiments were conducted in the present study: 1) the functional response of Amblyseius orientalis on different developmental stages of T. cinnabarinus, 2) prey preference of A. orientalis to different stages of B. tabaci and T. cinnabarinus, and between the most preferred stages of both species, and 3) the impact of the three prey treatments(B. tabaci only, T. cinnabarinus only, and a mix of both prey species) on A. orientalis development, reproduction, and population success. The main results were as follows:Functional response for on each stage(egg, larva or nymph) of T. cinnabarinus could be described by the HollingⅡtype. The suppression(a’/Th) of these three developmental stages of T. cinnabarinus by A. orientalis were 2.41, 3.32 and 2.91, separately; the daily maximum theoretic number of prey consumed were 43.75, 33.20 and 35.90, seprately.Among different stages of B. tabaci and T. cinnabarinus, A. orientalis preferred B. tabaci eggs and T. cinnabarinus protonymphs, respectively. When B. tabaci eggs and T. cinnabarinus protonymphs were provided together, no significant difference between the preference indices of the two prey types were detected(t=-1.940, df=201, p=0.054), which suggested a random predation pattern.Amblyseius orientalis is able to complete its life cycle on B. tabaci eggs, T. cinnabarinus protonymphs, or mixed prey. However, its developmental duration(7.22day) is 53.9% and 30.0% longer when reared on B. tabaci eggs than on T. cinnabarinus and the mixed prey, respectively. In addition, it produced only a few eggs and its intrinsic rate of increase was negative, which indicated B. tabaci is not sufficient to maintain A. orientalis population. The intrinsic rates of increase were 0.14 and 0.20 when A. orientalis fed on the mixed prey and T. cinnabarinus, respectively. It is reasonable to assume A. orientalis is able to increase its population when coexists with T. cinnabarinus.