Abstract

Two prominent pest species, the Onion thrips, Thrips tabaci Lindeman and the two-spotted spider mite Tetranychus urticaeKoch frequently co-occur in greenhouse crops. The generalist predator, Neoseiulus californicus (McGregor), is able to prey on both pest species; however, the presence of both T. tabaci and T. urticae may result in a preference of one prey species releasing the other prey species from predation. Thus, N. californicus protonmyphs, deutonymphs and females were simultaneously offered 1st T. tabaci instar larvae and different T. urticae developmental stages (larvae, protonymphs, deuto-nymphs, and adult females) to evaluate the prey preference and prey consumption rates of N. californicus and the body size ratios of predator and prey. Neoseiulus californicuspreferred to prey on T. urticae immatures. In contrast, all N. californicus developmental stages switched from T. urticae to T. tabaci , when T. urticae females were present, although T. urticae females were smaller than 1st T. tabaci instar larvae. Our results showed that N. californicus predators mainly prefer T. urticae as prey and consumptive effects of N. californicus onT. tabaci in the presence of T. urticae should be very low.