Primary sex‐ratio and differential progeny survivorship in solitary haplo‐diploid parasitoids

A method of partitioning emergence sex‐ratio to give estimates of primary sex‐ratio and male and female offspring survival from oviposition to emergence in solitary haplo‐diploid parasitoids is presented. This method is applied to sex‐ratio data from a larval parasitoid, Aphidius ervi Haliday, and a pupal parasitoid, Coccygomimus turionella L., parasitizing a range of host types. There was no evidence of facultative control of primary sex‐ratio in either species. Parasitoid emergence sex‐ratios were similar for all host sizes attacked by C. turionella. In contrast, emergence sex‐ratios of A.ervi showed a significant male bias in smaller hosts. This shift in emergence sex‐ratio was attributable to differential progeny survival. Pre‐emergence mortality in both species was a function of host size, with few offspring surviving from small hosts. This suggests that host size may be an important component in the dynamics of host‐parasitoid interactions. The evolution of sex‐ratio regulatory mechanisms in solitary haplo‐diploid parasitoids is discussed in the context of parasitoid life‐history. We suggest that there is a constraint to the evolution of the facultative control of primary sex‐ratio in parasitoids attacking larval stages as a result of the uncertainty of future host resource acquisition rates.