Life table studies of the walnut leaf beetle, Gastrolina depressa (Coleoptera: Chrysomelidae), with special attention to aggregation

Summary In order to make clear the relationship between the mortality processes and aggregation on the walnut leaf beetle, Gastrolina depressa, life tables of individual colonies were developed and the major mortality factor and the mode of its action were investigated. Furthermore, the influences of the larval colony size on the survival rate and the developmental period were also investigated in the laboratory. In the laboratory, when the larvae were reared on suitable (soft) host plants, the larger the group size, the faster the development. When the larvae were reared on unsuitable (hard) host plants, the larger the group size, the higher the survival rate. In the field, one of the major mortality factors of the egg stage was physiological death. However, there was no particular relation between the egg mass size and hatchability. On the other hand, another mortality factor of eggs, predation by A. hexaspilota, tended to act more on the larger sized egg masses. The mortality of the 1st instar larvae decreased with the increase of colony size. During the larval stages, the major mortality factor was predation by A. hexaspilota and P. japonica. Both predators tended to attack the colony in an all‐or‐none manner. The number of male adults was much less than the number of females in the Ina populations.