Geographical variation of sociality and size-linked color patterns in Lasioglossum (Evylaeus) apristum (Vachal) in Japan (Hymenoptera, Halictidae)

Lasioglossum (Evylaeus) apristum was studied at 2 localities in Japan. By rearing bees in a greenhouse in Matsue (lat. 35 degrees 29', alt. 170 m), south-western Japan, it was revealed that the bees had an eusocial life cycle with 2 distinctly discrete brood rearing periods, i.e., a solitary phase in spring and an eusocial phase in summer. The life cycle and sociality were of the same pattern as those at Mt. Daisen (lat. 35 degrees 22'. alt. 800-1000 m), 50 km from Matsue, where females reared in the greenhouse were collected. On the other hand in Sapporo (lat. 43 degrees 03', alt. 20 m), northern Japan, the solitary life cycle was suggested by a phenological survey. The effective accumulative temperature was compared for each locality, as an index of local thermal condition. The accumulative value at Mt. Daisen and Sapporo did not differ. The fact suggests that short flying season at high latitudes, such as in Sapporo does not induce the solitary life cycle in L. apristum. Approximately 39% of workers in the eusocial colonies at Matsue had well-developed ovaries, suggesting that they were possible egg-layers. No clear proof of the allocation of foraging in relation to the size and age of workers was obtained. Uninseminated, small, worker-sized females were also produced together with new queens at autumn at Mt. Daisen. Hibernation by these uninseminated females was suggested. The size-linked color patterns of the metasoma were recognized among the pre-hibernating females at both localities.