Antipredatory effects of inhabiting psyllid galls in the spider mite Eotetranychus asiaticus (Acari: Tetranychidae).

Leaf structures influence the community structure of small arthropods on the leaf surface. For example, several taxa of mites, primarily fungivorous and carnivorous, use domatia as refuges, leading to direct and indirect interactions among predators, prey and plants. However, the impact of insect-induced leaf deformities (galls and leaf shelters) on the mite community remains poorly understood. In this study, we focused on a population of Eotetranychus asiaticus (Acari: Tetranychidae) colonising the galls formed by psyllid larvae (Trioza cinnamomi, Hemiptera: Triozidae) on the leaves of Cinnamomum yabunikkei (Lauraceae). We tested the hypothesis that inhabiting galls benefits E. asiaticus by reducing egg predation. In the field, almost all E. asiaticus individuals were found inside galls (96.7%). This spider mite inhabited 3.4% of the observed galls and reproduced within them, whereas leaves without galls hosted few mites. Predatory mites and Feltiella larvae used galls near those occupied by spider mites, indicating high predation pressure on the leaf surface. Laboratory experiments revealed that the proportion of eggs predated by Neoseiulus womersleyi (Phytoseiidae) females was lower on leaves with galls than on leaves without, suggesting that gall use provides an antipredatory advantage. In conclusion, psyllids indirectly assist the coexistence of E. asiaticus with predators by creating defensive microhabitats.