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Amblyseius orientalis (Ehara) (Acari: Phytoseiidae) is a native predatory mite species in China. It used to be considered as a specialist predator of spider mites. However, recent studies show it also preys on other small arthropod pests, such as Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). Experiments were conducted to investigate (1) prey preference of A. orientalis between Tetranychus cinnabarinus (Boisd.) (Acari: Tetranychidae) and B. tabaci, and (2) development, consumption and life table parameters of A. orientalis when reared on T. cinnabarinus, B. tabaci or a mix of both prey species. When preying on different stages of T. cinnabarinus, A. orientalis preferred protonymphs, whereas when preying on different stages of B. tabaci, A. orientalis preferred eggs. When these two most preferred stages were provided together (T. cinnabarinus protonymphs and B. tabaci eggs), A. orientalis randomly selected its prey. Amblyseius orientalis was able to complete its life cycle on B. tabaci eggs, T. cinnabarinus protonymphs, or a mix of both prey. However, its developmental duration was 53.9% and 30.0% longer when reared on B. tabaci eggs than on T. cinnabarinus and a mix of both prey, respectively. In addition, it produced only a few eggs and its intrinsic rate of increase was negative when reared on B. tabaci eggs, which indicates that B. tabaci is not sufficient to maintain A. orientalis population. The intrinsic rates of increase were 0.16 and 0.23 when A. orientalis was fed on the prey mix and T. cinnabarinus, respectively. These results suggest that although B. tabaci is a poor food resource for A. orientalis in comparison to T. cinnabarinus, A. orientalis is able to sustain its population on a mix of both prey. This predatory mite may thus be a potential biological control agent of B. tabaci when this pest co-occurs with the alternative minor pest T. cinnabarinus.

Amblyseius swirskii, native to the east and southeast Mediterranean region, is a successful biological control agent of whiteflies. In this study, we investigated intraguild predations (IGP) between each stage of A. swirskii and each stage of two Phytoseiid species that occur in China, Amblyseius orientalis and Neoseiulus californicus. When there was no whitefly egg provided as the extraguild prey, IGP between A. swirskii and A. orientalis, and between A. swirskii and N. californicus, was observed in 10 and 20 out of 35 combinations, respectively. When IGP was observed, A. swirskii was the intraguild predator in 70% and 65% cases of A. orientalis and N. californicus predation, respectively. These results suggest that A. swirskii is a more aggressive intraguild predator compared to either A. orientalis or N. californicus. When whitefly eggs were provided as the extraguild prey, IGP between A. swirskii and N. californicus decreased greatly, but no significant decrease of IGP was observed between A. swirskii and A. orientalis. Amblyseius swirskii was able to complete development on both heterospecific predatory mites, and both heterospecific predatory mites completed their development on A. swirskii. Possible impacts that A. swirskii may have on local predatory mite populations in China are discussed.

Life style of phytoseiid species (Acari: Mesostigmata) is an important feature in evaluating their potential as biological control agents. Previous studies suggested that some morphometrics of gnathosoma are related to the feeding habits of phytoseiids. In this study, we showed it is appropriate to estimate feeding habits and/or life styles of phytoseiids based on variations in gnathosoma morphology. Scanning electron microscope pictures of 10 phytoseiid species belonging to four major life styles were taken. For each species, 23 morphometrics of gnathosoma and the length of dorsal shield were measured. Principle Component Analysis (PCA) showed that the 10 species can be divided into three groups based on the first two principle components of these parameters. The 1 st group includes one specialized predators of Tetranychus species (Phytoseiulus persimilis) and two selective predators of tetranychid mites (Neoseiulus pseudolongispinosus, Neoseiulus californicus), the 2 nd group includes six generalist predators (Amblyseius orientalis, Amblyseius swirskii, Amblyseius tsugawai, Neoseiulus barkeri, Neoseiulus bicaudus, Neoseiulus cucumeris), and the 3 rd group includes one specialized pollen feeder (Euseius utilis). This grouping is consistent with the life style division of McMurtry & Croft (1997), except that Type I and II were not separated. However, there is a trend that both Type II species were closer to each other. Overall, species in Group II have larger chelicerae and hypostome than those of Group I and III, while species in Group III have larger lobes and angle of fixed digit than those of the other two groups.

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Biological characteristics of a predator can be affected by the nutritional history of its prey, e.g., change in the nutritional components of prey may influence the development and reproduction of its predator. In this study, the predation, reproduction and conversion rate of a native predatory mite, Neoseiulus barkeri were compared when fed with two colonies of the flour mite Tyrophagus putrescentiae, the one reared on common wheat bran (TPA) and the other on a mixture of wheat bran and yeast (TPB). The experiments were conducted under laboratory condition at 25°C, 80% relative humidity, and 16:8 light:dark photoperiod. The daily consumption of unmated and mated N. barkeri females fed with TPB was 1.30 and 1.93 times higher than those fed with TPA. The daily and cumulative fecundity of mated predator females fed with TPB were 1.55 and 2.47 times, and their eggs being 1.20 times as those of females fed with TPA. The daily consumption of unmated females gradually decreased with age. For both mated and unmated females fed with TPA or TPB, we observed a wave pattern curve of daily prey consumption. The mean difference between two wave peaks was 3.55±0.23 days. It seems a periodic trend instead of random vibration due to the relative consist differences between wave peaks and similar sizes of the peaks. About 82% and 74% overall consumption of mated females offered TPA and TPB were allocated to reproduction, with corresponding conversion rate being 0.39 and 0.28, respectively. Overall, adding yeast to the diet of T. putrescentiae led to increased fecundity of N. barkeri mainly through stimulating its predation.

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