Chapter 23 - Sex Ratio and Quality in the Culturing of Parasitic Hymenoptera: A Genetic and Evolutionary Perspective

Abstract

Species of parasitic Hymenoptera are used extensively in biological control as agents for permanent suppression of a pest or as insectary-reared, augmentative agents for seasonal suppression of a pest. Both approaches require the agent to be cultured but the methods used to culture them often affect their quality, especially that of females. Poorly producing cultures frequently manifest detrimental sex-ratio changes, occasionally becoming entirely male with the consequent extinction of the culture. These sex-ratio changes arise from the interactions among conditions within the culture and factors such as sex determination, sex allocation, haplodiploidy, sex-ratio distorting elements, or unusual life histories of the parasitoids. In addition to the interaction between inbreeding and the sex-determining mechanisms, sex-ratio distortion due to several other factors that alter offspring sex ratios have been detected in Hymenoptera. Some of them have the potential to extirpate a culture or to reduce its productivity. Sex-ratio distorters in these cases involve heritable elements either within the genome or the cytoplasm and include such factors as sperm morphology, the paternal sex-ratio (PSR) element, primary male syndrome, maternal sex ratio, son-killer trait, nonreciprocal cross-incompatibilities, and thelytoky.