In most species, the numbers of sons and daughters are equal, and this 1:1 sex ratio is found generally in animals with large, randomly mating populations. Even sex ratios are a consequence of chromosomal sex determination (e.g. mammals, in which females are XX and males are XY). In animals with this kind of sex determination, there is little or no genetic variation for sex ratio. In Hymenoptera (bees, ants and wasps), however, sex is not determined in this way; female offspring arise from fertilized eggs, and males arise from unfertilized eggs. Sex ratios that regularly differ from 1:1 are found in parasitic wasps. The hosts of parasitic wasps are distributed in patches, so mating among the offspring from a patch is not random. When mating is not random throughout a population, there is no reason to produce more sons than are necessary to inseminate all the females, so the theoretically expected sex ratio is female-biased. Furthermore, theory predicts that there will be little genetic variation in sex ratio even when sex ratio is female-biased. Despite theoretical predictions, genetic variation in sex ratio has been demonstrated in a number of parasitic wasps. Muscidifurax raptor is a wasp that attacks the pupae of various fly species. It is used for biological control of houseflies and stableflies at poultry farms and cattle feedlots. The investigators will conduct a series of experiments that will describe the genetic variation in sex ratio and related characters like lifetime fecundity, longevity, and survival of offspring. Mechanisms that could maintain genetic variation for sex ratio will also be examined. This research also has applications for biological control because it will point out how artificial selection for sex ratio will affect other traits, and determine whether favored traits are expressed equally in all environments.
