Abstract

High predation and oviposition rates of the predatory mite Neoseiulus californicus when preying on onion thrips larvae (Thrips tabaci) suggest that this predator can be also used to control thrips.  However, spider mites (Tetranychus urticae) and thrips often co-occur in greenhouses, which may result in predation preference of N. californicus for spider mites over thrips larvae. Thus, we assessed the predation rates of adult females of N. californicus, when offered the first instar larvae of T. tabaci and different mobile developmental stages of T. urticae (protonymphs, deutonymphs, and adult females). For each predation preference treatment, the predator:prey body size ratios were determined. Neoseiulus californicus females were similarly sized as thrips larvae, but larger than the offered spider mite developmental stages. The females preferred immature spider mite stages over thrips larvae; however, they switched from spider mites to thrips larvae when female spider mites were offered. The predation preference of N. californicus females for T. urticae larvae, protonymphs and deutonymphs might be attributed to their smaller body size compared to thrips larvae. Consequently, these spider mite developmental stages seem to be easier to overwhelm and kill by the N. californicus females than thrips larvae. Although the spider mite females were smaller than thrips larvae, N. californicus females preferred the latter, which may indicate that the spider mite females had developed an efficient anti-predator behavior against N. californicus. Our results suggest that the consumptive effects of N. californicus on T. tabaci are low in the presence of spider mites.