Overwintering ecology of two species of spider mites (Acari: Tetranychidae) on different host plants.
The overwintering ecology of two species of spider mites was studied on different host plants in central Wakayama Prefecture, southwestern Japan. Starting from 20 October 1998, leaves of Clerodendrum trichotomum, Akebia quinata and peas were sampled for Tetranychus kanzawai infestation, while leaves of peas and chrysanthemums were sampled for T. urticae infestation. Sampling was continued at one-month intervals until mid-March. Laboratory diapause-inducing experiments showed that populations of T. urticae on peas and chrysanthemums both had a very low inherent capacity for diapause, and the population on chrysanthemums continued development and reproduction throughout the winter. On the other hand, populations of T. kanzawai had a genetically strong diapause capacity, regardless of the host species on which they occurred. However, the proportion of field-induced diapause females was lower in the population occurring on A. quinata, an evergreen host that had ample fresh leaves throughout the winter, than the populations on peas and C. trichotomum, a deciduous tree, the leaves of both of which deteriorated or defoliated in winter. The low incidence of diapause on A. quinata seemed due to weak diapause induction and/or earlier diapause termination in the plastic response to ample food conditions. On A. quinata, high proportions of eggs and immatures remained throughout the winter, suggesting that development and reproduction are possible throughout the winter in this area under ample food conditions.