Seasonal occurrence of Oligota kashmirica benefica Naomi (Coleoptera: Staphylinidae) on arrowroot and effect of prey consumption rate on development and oviposition

The seasonal population dynamics of a phytophagous mite (Tetranychus urticae (red form)) and its natural enemies were observed on a leguminous arrowroot, Pueraria lobata, in 1989. The mite population density showed a typical bimodal pattern with two peaks in June and October. A staphylinid, Oligota kashmirica benefica (O.k. benefica) was the most abundant insect predator, and its population trend was closely synchronized with that of its prey mite. Another Oligota species, O. yasumatsui, was observed at low density throughout the season. Among predacious mites, Amblyseius longispinosus was predominant and seemed to play a significant role as a natural enemy at low prey densities. Laboratory studies were conducted to clarify the predacious ability of O.k. benefica on the spider mite. Larvae of the beetle preyed on an average of 379.6 eggs of T. urticae (green form) each during the larval period at 25°C. The mean longevity of adult females was 73.9 days, and the average total number of prey consumed by an adult female was 7, 478.8 eggs. Females oviposited an average of 226.6 eggs in their life. These results suggest that the population dynamics of the beetle on arrowroot are affected by the population densities of spider mites, and the beetles have a significant effect on spider-mite populations.