Female-biased sex ratios in social insects lacking morphological castes.

Sex-investment ratios were measured in a Polistes exclamans population and found to be female-biased (1976, 74% females; 1979, 63% females) or close to even (1977, 58% females; 1978, 53% females). Sex ratios are female-biased in years of high levels of bird predation on nests and low overall nest success. Males emerge later from the nest so anything that results in an early end to the colony cycle decreases the numbers of males. Sex ratios on nests whose original queens were replaced by a mated worker did not differ from sex ratios on nests with original queens. Sex ratios may be generally female-biased because a female can become either a worker or a gyne, so females are a more flexible asset to a nest than are males. Thus, nests producing females before males may be able to produce greater total numbers of reproductives. This flexibility may be important for high reproductive success of nests given highly variable date of cool weather onset in central Texas.-from Author