CLUTCH SIZE IN A LARVAL PUPAL ENDOPARASITOID - CONSEQUENCES FOR FITNESS

1. Aphaereta minuta (Hymenoptera: Braconidae) is a gregarious larval-p upal endoparasitoid of many Diptera species. Several larval instars ca n be parasitized and the size differences between host species can be considerable. After parasitization, however, the host larva continues to grow and the parasitoid's eggs hatch after the host pupates. We que stion whether this delay between the moment of oviposition and that of resource availability for offspring development hampered the oviposit ing female in making optimal clutch size decisions.2. Using an optimal ity approach we analysed the relationship between clutch size (number of eggs) and fitness in different instars of the host Delia antiqua in the laboratory. 3. Clutch size was artificially manipulated, and the relationship between clutch size and fitness was quantified using the following parameters: offspring egg to adult survival, sex ratio of em erging adults and size of emerfing daughters (since size and number of eggs are positively correlated, size is a measure of fecundity). 4. S urvival to adult stage was slightly positively correlated with clutch size in first instar host larvae and negatively correlated with clutch size in second instar host larvae. Sex ratio (proportion daughters) i ncreased with increasing clutch size. The size of both males and femal es on emergence was negatively related to clutch size, and more strong ly to the number of emerging adults. 5. The calculated Lack clutrch si ze (whereby fitness is maximized per clutch) increased with larval hos t stage, as did the observed clutch size. 6. For each instar the obser ved clutch size was lower than the calculated Lack clutch size. We arg ue that under natural conditions females are selected to lay a clutch lower than the Lack clutch size.