Split sex ratios have been predicted in haplodiploid populations with high proportions of reproductive virgins, but there has been little empirical support. We found such split sex ratios in the gall-inducing thrips, Kladothrips rugosus. Sex ratios of juveniles from 96 galls were determined using chaetotaxy over two consecutive summers. The population-wide sex ratio was unbiased, but bimodal. Twenty-four per cent of galls only contained male juveniles. These galls were induced by a female that was probably a virgin. The mean sex ratio of all other galls was 0.36 ± 0.02, which is not significantly different from the theoretical evolutionarily stable sex ratio of 0.34, calculated from a previous model (Godfray, H.C.J. 1990. J. Evol. Biol. 3: 3-17) for 24% constrained females in a panmictic population. These data provide the first empirical support for the constrained sex allocation model of Godfray.
- Split-sex ratios