Superparasitism of Lygus hesperus Knight Eggs by Anaphes iole Girault in the Laboratory

Anaphes iole Girault is a solitary egg parasitoid which attacks Lygus spp. In a low-parasitoid-density experiment (parasitoid:host ratio = 1:40) 10.0% of available Lygus hesperus Knight eggs were superparasitized by A. iole. However, in experiments with a high parasitoid density (parasitoid:host ratio = 1:9), superparasitism of L. hesperus eggs was 33.3, 66.7, and 82.2% after exposure for 2, 6, and 24 h, respectively. Anaphes iole females were likely to superparasitize hosts previously parasitized by conspecific females, as 81.2% of such hosts were accepted for parasitization. High superparasitism rates resulted from a weak tendancy to discriminate against host eggs parasitized by a conspecific and a high rate of encountering such hosts at a high parasitoid density. Female parasitoids demonstrated an ability to discriminate against host eggs that they had recently parasitized, but it was not sufficient to prevent superparasitism from occurring at a high parasitoid density. Mean numbers of ovipositor piercing scars/host egg and parasitoid eggs/host egg increased with, but not in proportion, to the exposure period. The frequency of ovipositor penetrations, without egg deposition, also increased as the exposure period increased at the high parasitoid density. These data suggest that parasitoids are sensitive to some chemical and/or physical changes that occur both on the exterior and interior of the host egg, which causes the host egg to become less acceptable once it has been parasitized. The implications of superparasitization for mass rearing of these parasitoids are discussed.