Foraging strategies and patch distributions: intraguild interactions between Dicyphus hesperus and Encarsia formosa

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Ecological Entomology





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Abstract 1. Competing foragers are affected by the distribution of resources, but can also affect resource distribution. Intraguild predators may affect the distribution of both the shared prey and the intraguild prey, which are also their competitors. 2. Variation in foraging strategies and their effects on resource distributions may influence the outcome of intraguild interactions between an intraguild predator and its intraguild prey. This was tested using whitefly Trialeurodes vaporariorum as the shared resource, the parasitoid Encarsia formosa as the intraguild prey, and Dicyphus hesperus, an omnivore, as the intraguild predator on tomato (Lycopersicon esculentum) and mullein (Verbascum thapsus) plants, within enclosures in a greenhouse. Treatments were established with and without the intraguild predator and at high and low intraguild prey densities. 3. The interaction between D. hesperus and E. formosa showed significant asymmetry, with D. hesperus populations being unaffected by E. formosa densities, although E. formosa populations were reduced by the inclusion of D. hesperus. However, the inclusion of D. hesperus diminished density-dependent effects limiting E. formosa populations at high release densities. 4. Dicyphus hesperus reduced the average patch size and the proportion of patches occupied by whitefly. Increasing the release rate of E. formosa had no effect on any distributional measure. Based upon the foraging ecology of both species, the foraging activities of D. hesperus appear to have modified the patch distribution so that its foraging strategy becomes more successful than that of E. formosa. These properties may provide an important mechanism determining the outcome of species interactions.