SEX-RATIO MANIPULATION IN RESPONSE TO HOST SIZE IN THE PARASITOID WASP SPALANGIA-CAMERONI - IS IT ADAPTIVE

Many species of parasitoid wasps produce a greater proportion of sons in small than in large hosts. As described by the host-size model, natural selection is becoming a standard explanation for the evolution of this phenomenon. We examined a critical assumption of the host-size model, that host size has a more positive effect on female than on male reproductive success. In laboratory experiments with the parasitoid wasp Spalangia cameroni, females that developed on larger hosts contained more eggs at emergence. However, more eggs did not translate into more offspring, at high or low density and regardless of whether a female had to burrow to reach hosts. The size of host on which a female developed was also unrelated to her longevity, regardless of the presence or absence of hosts. The size of host on which a male developed had no effect on his sperm production or ability to inseminate females, regardless of whether insemination ability was measured by the amount of sperm transferred to a female, by the proportion of a male's mates that produced any daughters, or by the proportion of daughters that a male's produced. Thus, despite data on multiple measures of fitness under a range of conditions, sex ratio manipulation in response to host size, host size, Hymenoptera, parasitoid wasps, Pteromalidae, reproductive success, sex allocation, sex ratio.