Maternal body size affects sex allocation in a gregarious parasitoid

In parasitoid wasps, body size is a key predictor of reproductive success, as size is often correlated with increased gamete production. In Hymenoptera, due to haplodiploid sex determination, sperm are required to produce daughters but not sons, so sex allocation relies on a female's ability to obtain and manage a finite supply of sperm. Body size may, therefore, affect sex allocation if smaller males provide fewer sperm, or if larger, more fertile females deplete their sperm supplies by fertilizing more eggs. We examined the importance of male and female body size on offspring production and sex allocation in the parasitoid, Nasonia vitripennis (Walker). We predicted larger females would experience constrained sex allocation due to limited sperm, especially if mated with smaller males. We categorized 80 males and 80 females by size (large or small) into 4 mating groups: large females with large or small males, and small females with large or small males. We analyzed brood size and offspring sex ratios after each female oviposited on 12 pupae of Sarcophaga bullata (Parker). Overall, larger females produced more offspring and a greater proportion of males. Sex ratios became more male-biased with increased offspring production, indicating that sperm depletion had affected sex allocation in larger females. In contrast, male size did not affect sex allocation, but exhibited a small positive effect on females' offspring production. Our study highlights a complex relationship between body size, fecundity, and sex allocation, enhancing our understanding of reproductive strategies in haplodiploid organisms.