Shared enemies exert differential mortality on two competing parasitic wasps

Extrinsic Inter- and Intraspecific Competition in Parasitoid Wasps

The diverse ecology of parasitoids is shaped by extrinsic competition, i.e., exploitative or interference competition among adult females and males for hosts and mates. Adult females use an array of morphological, chemical, and behavioral mechanisms to engage in competition that may be either intra- or interspecific. Weaker competitors are often excluded or, if they persist, use alternate host habitats, host developmental stages, or host species. Competition among adult males for mates is almost exclusively intraspecific and involves visual displays, chemical signals, and even physical combat. Extrinsic competition influences community structure through its role in competitive displacement and apparent competition. Finally, anthropogenic changes such as habitat loss and fragmentation, invasive species, pollutants, and climate change result in phenological mismatches and range expansions within host-parasitoid communities with consequent changes to the strength of competitive interactions. Such changes have important ramifications not only for the success of managed agroecosystems, but also for natural ecosystem functioning.

The Ecology of Hyperparasitoids

Hyperparasitoids are some of the most diverse members of insect food webs. True hyperparasitoids parasitize the larvae of other parasitoids, reaching these larvae with their ovipositor through the herbivore that hosts the parasitoid larva. During pupation, primary parasitoids also may be attacked by pseudohyperparasitoids that lay their eggs on the parasitoid (pre)pupae. By attacking primary parasitoids, hyperparasitoids may affect herbivore population dynamics, and they have been identified as a major challenge in biological control. Over the past decades, research, especially on aphid- and caterpillar-associated hyperparasitoids, has revealed that hyperparasitoids challenge rules on nutrient use efficiency in trophic chains, account for herbivore outbreaks, or stabilize competitive interactions in lower trophic levels, and they may use cues derived from complex interaction networks to locate their hosts. This review focuses on the fascinating ecology of hyperparasitoids related to how they exploit and locate their often inconspicuous hosts and the insect community processes in which hyperparasitoids are prominent players.