Variable host quality, life-history invariants, and the reproductive strategy of a parasitoid wasp that produces single sex clutches

Abstract

The parasitic wasp Achrysocharoides zwoelferi (Hymenoptera, Eulophidae) produces clutches consisting of only one sex. Moreover, male clutch size is invariably one while female clutches are in the range one to four. We designed field experiments to determine the effect of host quality on clutch composition. We found that solitary male and solitary female clutches were reared from the same size mines, and that larger mines tended to produce gregarious female clutches. A higher proportion of male clutches were placed in older hosts, despite their large size. Variation in body size, both between and within clutches, was measured in order to test the predictions of models that take into account the constraint that clutch size is an integer trait, something of potential importance when absolute clutch size is low. Our data supported several predictions of these models, including the trade-off-invariant rule for optimal offspring size developed by Charnov and Downhower. However, while most invertebrate clutch size models assume equal resource share among members of the same clutch, we found an increase in inequality in larger clutches. Key words: body size, clutch size, Hymenoptera, sex allocation, sex ratio, trade-off. [Behav Ecol 12:577–583 (2001)]