Life cycles and interactions in spider mites (Acari: Tetranychidae) on dwarf bamboo, Sasa senanensis (F. & S.) (Poaceae), in Japan

Abstract

To clarify the interactions among mite species coexisting on the same plant, we determined the population dynamics of five spider mites (Acari: Tetranychidae) and their predators (Phytoseiidae, Stigmaeidae) appearing on dwarf bamboo, Sasa senanensis (Franchet and Savatier) (Poaceae), which has a high degree of structural heterogeneity in leaf pubescence. Tetranychid mites, Aponychus corpuzae Rimando, Panonychus bambusicola Ehara and Gotoh and Stigmaeopsis longus (Saito) preferred glabrous leaves, whereas Schizotetranychus recki Ehara and Yezonychus sapporensis Ehara, and the predators Agistemus summersi Ehara (Stigmaeidae) and Phytoseius tenuiformis Ehara (Phytoseiidae) preferred hirsute leaves. Species living on glabrous leaves tended to avoid species living on hirsute leaves. However, three species that prefer glabrous leaves sometimes coexisted with and sometimes avoided species that prefered hirsute leaves. Each species probably has some range of leaf hairiness that they tolerate and prefer. The presence of leaf hairs along the midvein of the lower surfaces of the leaves are especially important because they increase the acceptable range for coexistence of species preferring glabrous or hirsute leaves. Stigmaeopsis longus coexisted with Typhlodromus bambusae Ehara, which is a species-specific predator of St. longus. Yezonychus sapporensis coexisted with Ag. summersi, which is a predator of Y. sapporensis and Sc. recki. The population density of each spider mite species produced one to three peaks in spring, autumn and/or early winter depending on the species and the census periods. Phytoseius tenuiformis accounted for most of the phytoseiid mites on Sasa leaves and occurred on the most hirsute leaves. Almost all phytoseiid mites collected in the nests of the spider mite St. longus were T. bambusae. The critical photoperiods of five spider mite species ranged from 13.5 to 14.5 h at 18°C, which occured between late August and mid-September in Sapporo. The dates by which 50% or more individuals entered diapause were between late August and late September, roughly corresponding with timing predicted by the critical photoperiods. The maximum number of generations that could be produced in a year was estimated as four or five based on the total degree-days accumulated above the lower temperature threshold (10.2-12.1°C) of five spider mite species and the thermal constant (164.5-217.7 DD) of these mite species.