Colemegilla maculata (Coleoptera : Coccinellidae) predation on pea aphids promoted by proximity to dandelions

The impact of a predator on its prey may depend on the presence of other sp ecies in the community. In particular, if predators are attracted to areas containing one prey species, another prey species may suffer greater predat ion if it occurs in the same areas. If the predator is omnivorous, this may occur even if one prey species is an animal and the other is a plant. We i nvestigated the role of local dandelion densities on the impact of the pred ator Coleomegilla maculata on pea aphids in alfalfa fields. At small spatia l scales, increased dandelion densities were associated with high C. macula ta densities, presumably because these omnivorous ladybird beetles aggregat ed to pollen resources. In turn, the high C. maculata densities were associ ated with low aphid densities, presumably because of increased predation. W e used laboratory cages to simulate C. maculata foraging in two adjacent pa tches of alfalfa, one with dandelions and one without. As in the field, the laboratory experiment showed that C. maculata aggregated to alfalfa inters persed with dandelions, which resulted in increased predation on aphids on alfalfa. This study demonstrates that a pollen-producing plant can indirect ly decrease nearby herbivore densities by attracting an omnivorous predator .