Host preference and offspring performance are linked in three congeneric hyperparasitoid species

1. The optimisation theory predicts that insect mothers should oviposit on resources on which they attain the highest exclusive fitness. The development of parasitoid wasps is dependent on limited host resources that are often not much larger than the adult parasitoid. 2. In the present study preference and development in three congeneric species of secondary hyperparasitoids attacking cocoons of two congeneric primary parasitoids that differ significantly in size were compared. Gelis agilis ( F abricius) and G . acarorum ( L .) are wingless hyperparasitoids that forage in grassy habitats, whereas G . areator ( P anzer) is fully winged and forages higher in the canopy of forbs. 3. The three species were reared on cocoons containing pupae of a small gregarious endoparasitoid, C otesia glomerata ( L .), and a larger solitary species, C . rubecula ( M arshall), both of which develop in the caterpillars of pierid butterflies. 4. Adult mass was correlated with initial cocoon mass in all three species, whereas development time was unaffected. Wasps were larger when developing in C . rubecula . However, for a given host mass, wasps were larger when developing on the smaller host, C . glomerata . This suggests that there is a physiological limit to hyperparasitoid size that was exceeded when C . rubecula served as host. 5. All three hyperparasitoids strongly preferred to attack cocoons of the larger species, C . rubecula , often avoiding cocoons of C . glomerata entirely. 6. Preference and performance are correlated in the three G elis species. However, owing to variation in the distribution and thus abundance of their hosts, it is argued that cumulative fitness may be still higher in the smaller host species.