The stealthiness of predatory mites as spider mite biological control agents

Abstract

Adult spider mite females that are aware of predatory mites can reduce predation by dispersing from patches invaded by predators or by shifting their oviposition site onto webs where eggs are predated less than on leaf surfaces. Therefore, the stealthiness of predatory mites stalking spider mite females should largely determine the success of spider mite control. This study examined the stealthiness of three predatory mites: Phytoseiulus persimilis Athias-Henriot, Neoseiulus californicus McGregor, and Neoseiulus womersleyi Schicha. The first two species have been commercialized as spider mite biological control agents, whereas the last species is a native predator of spider mites in Japan. We measured two indices of predator stealthiness in bioassays using Tetranychus kanzawai Kishida as prey: the proportion of prey mites that dispersed from their patches in response to predator intrusion and the proportions of prey eggs laid on webs in response to predator eggs. Both indices resulted in the same ranking, with P. persimilis ranking highest and N. womersleyi lowest. The greater stealthiness of P. persimilis eggs compared with N. womersleyi eggs seemed to be due to the lower amount of detectable substances on the egg surface. We also measured this index of stealthiness for European and Japanese Tetranychus urticae Koch populations and found that they had the same stealthiness ranking as measured using T. kanzawai. Therefore, we predict that the stealthiness of predatory mites is consistent across prey species and could be an effective index, along with conventional indices, for evaluating predatory mites as spider mite biological control agents.