Host plant manipulation of natural enemies: leaf domatia protect beneficial mites from insect predators

Acarodomatia are small tufts of hair or invaginations in the leaf surface a nd are frequently inhabited by several taxa of non-plant-feeding mites. For many years, ecologists have hypothesized that these structures represent a mutualistic association between mites and plants where the mites benefit t he plant by reducing densities of phytophagous arthropods and epiphytic mic roorganisms, and domatia benefit the mite by providing protection from stre ssful environmental conditions, other predaceous arthropods, or both. We te sted these hypothesized benefits of domatia to domatia-inhabiting mites in laboratory and growth chamber experiments. In separate experiments we exami ned whether domatia on the wild grape, Vitis riparia, provided protection a gainst drying humidity conditions or predaceous arthropods to two species o f beneficial mite: the mycophagous species Orthotydeus lambi, and the preda ceous species Amblyseius andersoni. For both taxa of beneficial mite, domat ia significantly increased mite survivorship in the presence of the predato ry bug, Orius insidiosus and the coccinellids Coccinella septempunctata and Harmonia varigata, There was no evidence for a protective effect of domati a with a third species of predatory arthropod, lacewing larvae Chrysoperla rufilabris. In contrast, there was no evidence for either species of benefi cial mite that domatia provided any protection against low humidity. Thus i n this system the primary mechanism by which domatia benefit beneficial mit es is by protecting these organisms from other predatory arthropods on the leaf surface.