Differences in diapause attributes between two clinal forms distinguished by male‐to‐male aggression in a subsocial spider mite, Schizotetranychus miscanthi Saito

The nest‐weaving spider mite Schizotetranychus miscanthi Saito showed a cline in male‐to‐male aggression intensity with minimum winter temperature. The altered kin structure in spring nests, which might be caused by winter harshness, was hypothesized to be a key factor responsible for the cline in male‐to‐male aggression. In Japan, we found two forms (high‐ and low‐aggression forms) that showed different clinal trends with similar regression slopes and different intercepts. The former is characteristic of local populations from milder climates, whereas the latter occurs in harsher climates. We hypothesized that the intensity of female diapause, which may determine whether males are produced during late winter, was one of the factors separating these two clinal forms. In the four populations studied, short day length during the developmental period (egg to adult emergence) induced diapause in females. Diapause intensity varied greatly among populations, and particularly between the high‐aggression and low‐aggression forms. These data, together with data on winter harshness between the localities, led us to believe that female diapause is one of the factors affecting relatedness between interacting males in nests and can explain why the two forms of S. miscanthi have different clinal trends in male aggression in Japan.