Aggregation in field parasitoid populations: foraging time allocation by a population of Diadegma (Hymenoptera, Ichneumonidae)

Abstract

1. A field study was made of foraging time allocation by a population of parasitic wasps, Diadegma spp. (Ichneumonidae), to plants containing different densities of their hosts, the caterpillars of Pkutella xylostelka (L.). 2.The parasitoid population exhibited a clear aggregative response, spending more total time on higher density patches, which probably resulted from wasps making more and longer visits to these densities.3. Despite this aggregation, positive density dependent parasitism was not found. The functional response of the Diadegma population exhibited an upper asymptote at high host densities, probably due to an increase in the proportion of time spent handling hosts, which countered the effect of aggregation.4. While Diadegma may select and forage preferentially on plants with higher host density, they d o not exhibit the tendency, predicted by some optional foraging models, to exploit progressively less profitable plants during a foraging bout. Some factors affecting patterns of parasitoid foraging in the field are discussed.

Density-Related Mortality in Cameraria hamadryadella (Lepidoptera: Gracillariidae) at Epidemic and Endemic Densities

“…Birds are the major predators of C. hamadryadella larvae and pupae, particularly members of the genus Parus. We have observed predation scars on leaf-mines that appear to be caused by invertebrate Density estimates In , 1983In , 1988In , 1989In . and 1991 (Connor 1991).…”

“…Sinee death due to host resistanee and intraspecifie competition are positively spatially density-dependent, the chance that the pattern of parasitism would appear to be density-independent or inversely densitydependent is increased. In addition, sinee C. hamadryadella occurs at densities of fewer than 0.1 individual/leaf in most years and locations, the ability of parasitoids to respond to high host densities may be constrained evolutionarily by their rates of searching, handling, and egg productitin (Hassell 1982, Waage 1983, Hassell et al 1985.…”

Foraging Behavior and Patch Time Allocation by Fopius arisanus (Hymenoptera: Braconidae), an Egg-Larval Parasitoid of Tephritid Fruit Flies

“…An effective parasitoid should concentrate search in areas of high quality host patches to maximize its rate of host attack (Waage, 1983;Wang and Keller, 2002). The present study documents the foraging behavior of Fopius (= Biosteres) arisanus (Sonan), a solitary endoparasitoid attacking eggs of tephritid fruit flies, and describes the effect of host patch quality on the parasitoid's patch residence time.…”

Testing the impact of laboratory reared indigenous leafroller (Lepidoptera: Tortricidae) parasitoids (Hymenoptera: Ichneumonidae, Braconidae) on sentinel hosts in controlled orchard releases

“…Lightbrown apple moth, Eiphyas postvittana (Walker) (Lepidoptera: Tortricidae) larvae, exit webbing on leaves and spin down or crawl over the leaf surface when probed by the parasitoid Dolichogenidia tasmanica (Hymenoptera: Braconidae) (Suckling et al, 2001) and diamond-back moth, Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae) larvae, have been observed to hang by silk from plant leaves after attack by Diadegma spp. (Hymenoptera: Ichneumonidae) (Waage, 1983). Host escape behaviour in response to parasitoid probing in the orchard may cause a leafroller larva to move away from its feeding site, making it more vulnerable to movement off the tree and mortality from predation, starvation or desiccation.…”