Relationship between offspring survival and host selection: case of a solitary parasitoid Pachycrepoideus dubius [Hymenoptera: Pteromalidae]

In solitary parasitoids, only one individual can emerge per host. Therefore, females should reject already parasitized hosts. However, when unparasitized hosts are scarce, superparasitism becomes advantageous and females should choose hosts that offer the best survival chances to their progeny, which depend on the developmental stage of the first parasitoid. In ectoparasitoids, the first larval instar is generally considered as the fighting stage, the only one involved in larval competition. We tested this hypothesis in Pachycrepoideus dubius, a solitary ectoparasitoid. Our results show that all the larval instars are combative, the later instars winning the competition more often. Nevertheless, as soon as the first parasitoid has reached the pre-pupal stage, the competition ends and both individuals can complete their development. Moreover, choice experiments show that the acceptation rate of hosts presenting larvae of different ages is perfectly correlated to the offspring survival rate when the first parasitoid is less than 10 days old. When the first parasitoid has reached the pre-pupal stage, females tend to reject these hosts while offspring survival rate is about 40%. This discrepancy between female choice and survival rate of their offspring is discussed.