Halictus sexcinctus is a large halictine bee species widely distributed across central Europe and into the Middle East. Although its behaviour had not previously been studied in detail, it is known to exhibit solitary behaviour in central Europe. An aggregation nesting beside the seashore at Pyla-Daimonia, Demos Molai, in the southeastern Peloponnesos, Greece, was studied during the summers of 1997 and 1998. In southern Greece, H. sexcinctus exhibits weakly eusocial colonies, based on a partially bivoltine colony cycle, so across its range it is socially polymorphic. Weak eusociality in this Mediterranean population is characterized by haplometrotic nest-founding, a relatively high degree of queenworker size dimorphism, high rates of worker mating and ovarian development, relatively short queen life-spans, and relatively low second-brood productivity. Overall, the sex ratio of the first brood is highly female-biased, while that of the second brood is variable, the proportions of males and females varying significantly in the 2 years. An unusual characteristic of nest foundresses in this population is that some are un-inseminated and produce all-male first broods rather than workers.
