Nesting Biology and Occurrence of Social Nests in a Bivoltine and Basically Solitary Halictine Bee, Lasioglossum (Lasioglossum) scitulum Smith (Hymenoptera : Halictidae)

The life cycle and sociality of the halictine bee, Lasioglossum (Lasioglossum) scitulum were studied in a greenhouse at Matsue (lat. 35°22′N), south-western Japan in 1988 and 1989. This species was a bivoltine bee with solitary to primitively social behavior. During the summer brooding period of 1988, 51 solitary nests and 8 multi-female nests (3 matrifilial and 5 sororal nests) were discovered. In 1989, 11 multi-female nests (3 matrifilial and 8 sororal nests), together with 59 solitary nests were also found. Although summer females mostly dispersed and nested solitarily, some of them stayed in their natal nests and formed sororal social nests. When oviposition by mother bees was extended until the emergence of her daughters, matrifilial nests were formed. Multi-female nests usually were composed of 2 cohabitants. Task allocation between them was relatively distinct in foraging activity. Usually, both cohabitants had well developed ovaries, suggesting that they both were egg-layers. Reproductive efficiency (=number of provisioned cells produced/day/female) in the sororal nests was conspicuously lower than that in the solitary nests. Probably, multi-female nests arise accidentally when more than one female remained in their natal nests. The lack of some social traits such as ovarian inhibition and behavioral conflict indicates that L. scitulum is basically solitary species.