Nature 331, 346 - 348 (28 January 1988); doi:10.1038/331346a0

Local resource enhancement and sex ratios in a primitively social bee

Michael P. Schwarz

Department of Zoology, La Trobe University, Bundoora, Victoria 3083, Australia

'Queen-worker conflict'¹ and 'local mate competition'^2,3 have frequently been used to help explain female-biased sex ratios in the social Hymenoptera. In this report I show that neither of these theories is able to explain brood-size dependent sex ratios in an allodapine bee, Exoneura bicolor. Most nests of this species contain two or more related females, and reproductivity per female increases as a function of the number of individuals cooperating in joint nest use. I argue that 'local resource enhancement' may explain sex-ratio bias in this species and that similar bias may be expected in other presocial insects.

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