SUPERPARASITISM AND MUTUAL INTERFERENCE IN THE EGG PARASITOID ANAGRUS-DELICATUS (HYMENOPTERA, MYMARIDAE)

1. In nature, interference among Anagrus delicatus (Hymenoptera: Mymaridae) parasitoids reduced the per-capita number of hosts parasitized. Interference increased with parasitoid density. 2. Anagrus delicatus did not avoid parasitizing hosts that had recently been parasitized by conspecific wasps. Evidence indicated that this superparasitism was largely a random process, increasing with the ratio of parasitized to unparasitized hosts. 3. Individual parasitoid efficiency, the number of hosts killed per wasp per unit time, decreased with increasing wasp density. This occurred whether wasps searched the patch together (simultaneously) or one by one (sequentially), and was the result of an increase in time spent superparasitizing hosts at higher wasp density. This is known as indirect mutual interference. 4. Increasing numbers of parasitoids together on the same patch caused a significant decline in the rate and per-capita number of hosts parasitized. However, there was not a correspondent decline in searching efficiency with increasing wasp density (i.e. no direct mutual interference). 5. These forms of parasitoid density dependence should contribute to the stability of the host-parasitoid interaction.