Parasitoid theory: From aggregation to dispersal.

Models that stabilize the Nicholson-Bailey equations of population interactions have dominated theory about insect pests and their natural enemies. However, nonequilibrium behavior is conspicuous in real interactions, and versions of these models that are based on extremely concise descriptions of aggregation of risk to pests are simplistic in ignoring density relationships and movement within generations. Recent theory is less concerned with equilibrium. Within generations, attention to details of enemy movement, foraging and aggregation leads to models that actually predict pest mortality patterns for specific cases. Among generations, dispersal is a key facet of nonequilibrium persistence. Dispersing parasitoids can cause high local mortalities of host insects.