On the robustness of split sex ratio predictions in social hymenoptera

Using inclusive fitness models, this study determines the optimal patterns of split-sex-ratio allocation for hymenopteran workers when colonies have a single queen, and queens mate with either one or two males. This particular colony kin-structure is common in social Hymenoptera. Importantly, the basic split-sex-ratio pattern of allocation, with some colonies producing exclusively or largely males and the others producing exclusively or largely queens, is shown to be robust with respect to the parameters investigated: errors in the assessment of queen mating frequency by workers, male-production by workers, unequal male contributions to paternity in double-mated queens, and partial queen control. Conditions under which split sex ratios are not expected, or may be non-extreme, are discussed. (C) 1997 Academic Press Limited.