Life cycle and social behavior in a heathland population of the allodapine bee, Exoneura bicolor (Hymenoptera: Apidae)

Previous studies of the allodapine bee Exoneura bicolor have utilised a predominantly social population from tall montane forests. In this report we examine aspects of the sociality and biology of a population from subcoastal heathland in western Victoria, Australia. Entire colonies, nesting in Xanthorrhoea minor, were collected at monthly intervals over 12 months between February 1989 and January 1990. In addition, three collections from Melaleuca squarrosa were made over three consecutive winter months. The heathland population differs from the montane population in several aspects associated with sociality: (i) it shows lower levels of co-occupancy in both newly founded and re-used nests; (ii) foundress dispersal occurs over a larger proportion of the year; and (iii) there may be a partical second brood produced in late summer, during and after adult eclosion of the first brood. The occurrence of a partial second brood gives rise to opportunities for sib-rearing and eusociality. Colony sizes tend to be larger in M. squarrosa than X. minor, but still smaller than colonies from the montane population. Egg-laying commences several weeks earlier in multifemale colonies than in single female colonies, before spring dispersal begins. It appears that multifemale colonies are more successful at preventing brood loss than single females and that the mean number of brood per female is larger in multifemale colonies than in single female colonies. These two populations, which display differences in several life history traits, provide an ideal system for studying the mechanisms maintaining social behavior.