Sex ratios of commercially reared biological control agents

We purchased samples of 27 parasitoids, six coccinellid beetles, and the predatory 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 0.77 (proportion males), and none of the predator sex ratios differed significantly from 0.5. Among the parasitoids, we found no significant effect of taxonomic affiliation (family, superfamily) or life history (gregarious vs solitary development) on the sex ratio. The pteromalid parasitoids Muscidifurax raptorellus (Kogan and Legner), M. zaraptor (Kogan and Legner), and Nasonia vitripennis (Walker) and the eulophid Diglyphus isaea (Walker) all had significantly male-biased sex ratios, and an additional five species that did not have male-biased sex ratios had sex ratios that had a higher proportion 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 (Trichogrammatidae), and Pediobius foveolatus (Crawford) (Eulophidae). This suggests that it may be possible to increase the proportion of females produced by these species under conditions of commercial rearing. In the rest of the 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 potential explanations for the sex ratios that we found, as well as implications of the results for mass rearing. (C) 2000 Academic Press.