LIFE-HISTORY AND SOCIAL EVOLUTION OF THE PRIMITIVELY EUSOCIAL BEE AUGOCHLORELLA-STRIATA (HYMENOPTERA, HALICTIDAE)

Life history parameters of the primitively eusocial bee Augochlorella striata (Hymenoptera: Halictidae) are summarized for a population in c entral New York, and analyzed with respect to the evolutionary mainten ance of eusociality in this species. High mortality (39%) of solitary foundresses and low mortality (12%) of social colonies indicate severe ecological constraints limiting independent (solitary) reproduction. Extreme relatedness asymmetries (3:1, due to singly-mated queens) and female-biased reproductive broods create genetic incentives favoring w orker behavior (helping). In addition, workers appear to capitalize on relatedness asymmetries by biasing the sex ratio towards their more c losely related sisters and away from their more distantly related brot hers, because eusocial colonies (headed by a mother queen; relatedness asymmetry present) consistently produce more female-biased sex ratios than parasocial colonies (headed by a sister queen after queen supers edure; relatedness asymmetry absent). Both intrinsic factors inherent in the haplo-diploid system of sex determination (relatedness asymmetr ies in conjunction with female-biased sex ratios) and extrinsic factor s (ecological constraints) therefore appear to modulate eusocial evolu tion in A. striata.