Adult female Neoseiulus womersleyi feed on all stages of tetranychid mites, although they show a strong preference for eggs over adult females when both are available. We found that the oviposition rate of N. womersleyi females supplied with eggs of Tetranychus kanzawai or T. urticae was significantly higher than that of N. womersleyi females supplied with adult females of the respective prey species. The results suggested that the preference of N. womersleyi females for spider mite eggs simply reflected the optimal foraging of the females.

We experimentally verified a proximate cause for the preference of prey species by the predatory mite Neoseiulus womersleyi, which prefers the eggs of Amphitetranychus viennensis Zacher to those of Tetranychus urticae Koch. To separate the effects of spider mite eggs and spider mite webs on the prey preference of the predatory mite, we manipulated combinations of eggs and webs of the two prey species. The number of eggs consumed by adult female N. womersleyi was compared with respect to two factors: eggs of the same species under webs of the different species and eggs of different species under webs of the same species. The results revealed that the prey preference of N. womersleyi was determined by the webs, and not by the eggs.

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