We tested 13 species of phytoseiid mites for prey preferences between eggs and larvae of twospotted spider mite, Tetranychus urticae Koch. In general, oligophagous, specialized spider mite predators preferred eggs whereas more polyphagous, generalist predators showed no prey-stage preference or preferred larvae: Phytoseiulus macropilis (Banks), P. persimilis Athias-Henriot, Neoseiulus longispinosus (Evans), and Neoseiulus fallacis (Garman) preferred eggs; Kampimodromus aberrans (Oudemans), Galendromus occidentalis (Nesbitt), N. barkeri Hughes, N. californicus (McGregor), N. cucumeris (Oudemans), and Typhlodromus pyri Scheuten showed no prey-stage preference; and Amblyseius andersoni Chant, Euseius finlandicus (Oudemans) and E. hibisci (Chant) preferred larvae. When the ratio of spider mite eggs to larvae was altered, adult females of E. finlandicus, G. occidentalis, N. fallacis, and P. persimilis maintained relatively constant feeding ratios, resulting in slight negative prey-stage switching due mostly to the changes in prey-stage ratios offered. However, when offered a prey-stage ratio that was biased toward eggs, adult females of T. pyri exhibited positive switching, feeding disproportionately more on eggs than would be expected given the change in the ratio offered. There was no clear trend in the effect of starvation time on prey-stage preference for N. fallacis adult females. The egg preference of N. fallacis was also not affected when individuals were reared solely on eggs or larvae of T. urticae and subsequently tested as adult females. Individuals of field-collected strains of N. fallacis and P. persimilis showed no differences in prey-stage preferences when compared with individuals from long-term reared laboratory strains of the same species. However, individuals of one field-collected strain of G. occidentalis showed a stronger preference for eggs than individuals from three other strains (one laboratory and two field-collected) of the same species.
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