Sex ratios of commercially reared biological control agents

We purchased samples of 27 parasitoids, six coccinellid beetles, and the pr edatory midge Aphidoletes aphidimyza (Rondani) from commercial insectaries and scored the sex ratios from groups of approximately 200 individuals from each of these samples. Parasitoid sex ratios ranged from all female to 0.7 7 (proportion males), and none of the predator sex ratios differed signific antly from 0.5. Among the parasitoids, we found no significant effect of ta xonomic affiliation (family, superfamily) or life history (gregarious vs so litary development) on the sex ratio. The pteromalid parasitoids Muscidifur ax raptorellus (Kogan and Legner), M. zaraptor (Kogan and Legner), and Naso nia vitripennis (Walker) and the eulophid Diglyphus isaea (Walker) all had significantly male-biased sex ratios, and an additional five species that d id not have male-biased sex ratios had sex ratios that had a higher proport ion of males than reported in the literature. These were Cotesia plutellae Kurdjumov (Braconidae), Dacnusa sibirica Telenga (Braconidae), Eretmocerus nr. californicus Howard (Aphelinidae), Trichogramma brassicae Bezdenko (Tri chogrammatidae), and Pediobius foveolatus (Crawford) (Eulophidae). This sug gests that it may be possible to increase the proportion of females produce d by these species under conditions of commercial rearing. In the rest of t he species studied (74% of species purchased), sex ratios either conformed to most published reports or had a higher proportion of females. We discuss the sex ratios of each species or group of species separately and review p otential explanations for the sex ratios that we found, as well as implicat ions of the results for mass rearing. (C) 2000 Academic Press.