Sex ratio and foundress number in the parasitoid wasp Bracon hebetor

As predicted by the theory of local mate competition, the offspring sex ratios of many parasitoid wasps become increasingly male biased as the number of conspecific females ovipositing in a patch rises. The braconid wasp Bracon hebetor appears to be an exception. Recent experiments have suggested that wasps ovipositing in the presence of a conspecific female produce more daughters than solitary wasps. Larval competition is more intense when two females oviposit together and it has been suggested that females lay fewer sons in these circumstances because the resultant small males have poor mating success. Experiments are reported that (1) compare the sex ratio of solitary and paired B. hebetor; (2) investigate the importance of differential mortality and (3) explore the relative mating success of small and large wasps. Paired and solitary wasps produced the same sex ratio and there was no evidence of differential mortality. Small males were able to mate both large and small females and, at least in the laboratory, appeared to suffer no disadvantage in competition with larger males. There are statistical problems with some previous analyses of sex ratio and foundress number in B. hebetor, and there are also problems in making inference about adaptation from inbred strains of a naturally outbred species.