Predators of the nest-making spider mite Schizotetranychus brevisetosus (Acari: Tetranychidae)

Several species of spider mites construct silk nests on leaf surfaces wherein they develop and reproduce (web-nesting species). Nesting patterns and behaviour of spider mites are related to predator avoidance, but the study of their influence on predatory fauna has been limited to species of a few genera. The present study investigates the occurrence of predators of Schizotetranychus brevisetosus , which make web nests and attack some predators, on evergreen oak in Kochi Prefecture, Japan. Of the total individual predators observed (n = 129), the highest proportion (38%) consisted of rove beetles Holobus spp. (Coleoptera: Staphylinidae), which are nest intruders and prey on mites at all stages of development. The second most abundant predators (26%) were Anystis spp. (Acari: Anystidae), which capture mites outside the nest. The common predators Phytoseiidae spp. (Acari) accounted for only 15% and were mostly found in hibernation. Other predators were rare, except for egg-eating Agistemus spp. (Acari: Stigmaeidae) (13%). The findings suggest that web nests and anti-predatory behaviours may bias the predatory fauna toward species that can cope with these anti-predatory strategies.