Host size selection and sex allocation behaviour among parasitoid trophic levels
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1. Sex ratio in the ectoparasitoid Chrysocharis nephereus, when attacking larvae of the lepidopteran leafminer Cameraria jacintoensis inhabiting the scrub oak Quercus dumosa, varies as a function of host size. 2. Female progeny are overproduced on large hosts and male progeny are overproduced on small hosts. Whether a host is perceived as large or small depends on the distribution of sizes of hosts encountered. Lastly, the primary sex ratio is consistently male biased. These patterns are not due to variation in progeny sex specific mortality, but are probably a result of maternal choice. 3. Female wasp size increases at a greater rate than does male wasp size with an equivalent increase in C.jacintoensis larval size. Although the average adult longevity of female C.nephereus is significantly greater than the average longevity of male C.nephereus, male wasp longevity increases at a greater rate than does female wasp longevity with an equivalent increase in C.jacintoensis larval size. 4. Chrysocharis nephereus developing on large C.jacintoensis are more likely to be hyperparasitized by Closterocerus sp. than are C.nephereus developing on smaller sized C.jacintoensis. Closterocerus sp. hyperparasitize female C.nephereus progeny with significantly greater frequency than male progeny. 5. Female C.nephereus overproducing daughters on large hosts and sons on small hosts may experience fitness trade-offs between the benefits associated with producing offspring on large hosts and costs associated with these offspring becoming hyperparasitized.
