Host discrimination, superparasitism and infanticide by a gregarious endoparasitoid

When a female parasitoid encounters a previously parasitized host she may reject it or accept and oviposit in/on it (superparasitism), frequently adding one or more eggs after killing some of the offspring in the initial clutch (infanticide). Herein we document these behaviours in a facultatively gregarious endoparasitoid wasp, Metaphycus flavus (Hymenoptera: Encyrtidae), when females encounter unparasitized and parasitized brown soft scales, Coccus hesperidum (Hemiptera: Coccidae), 2 h, 2 days or 4 days after their initial parasitism. We also report the consequences of such behaviours for their offspring survival. Females discriminated unparasitized scales from parasitized scales independent of the time elapsed since the first oviposition and they often oviposited on parasitized scales after killing some of the offspring in the first clutch. Immature parasitoid mortality was a dominant feature of this host–parasitoid interaction and it depended on the occurrence of superparasitism and the time interval between ovipositions. In single clutches, encapsulation of parasitoid eggs was the major source of immature mortality. Encapsulation rates decreased when a second clutch of eggs was added; consequently, superparasitism appears advantageous. When the time interval between ovipositions was long (2–4 days), encapsulation rates decreased again, but most of the younger larvae of the second clutch were consumed by the older larvae of first clutch in superparasitized hosts. Under these circumstances a female should avoid superparasitizing these hosts, or she should kill the eggs or larvae already present in it before allocating a clutch of eggs.