Manipulation of Myzus persicae, green peach aphid, and Leptinotarsa decemlineata, Colorado potato beetle, to determine predator distribution in potatoes

Generalist predators may search out prey species that are nutritious even when they are uncommon in the environment, such that rates of predation will not necessarily track prey abundance. This study examined patterns of predation for two species of insect predator, Nabis alternatus and Geocoris bullatus, in potato field plots where pest densities were experimentally manipulated using selective insecticides. In a subset of plots, we manipulated densities of green peach aphid (Myzus persicae) using Beleaf (Flonicamid), and/or densities of Colorado potato beetle (Leptinotarsa decemlineata) using Novodor (Bacillus thuringiensis Tenebrionis). In no-spray control plots, we withheld these sprays to allow pest populations to flourish. Predators were collected from each plot. PCR was used to test whether predators had eaten aphids or potato beetles, and whether N. alternatus had consumed G. bullatus. At the same time, the entire potato-insect community was sampled to determine total density and composition of other potential prey. We found that both predator species consumed Colorado potato beetles and aphids, and that Nabis consumed Geocoris. Predators found in plots with fewer Colorado potato beetles and green peach aphids nonetheless commonly consumed these prey items. This suggests that the predators search out both species of prey even when rare, perhaps because they provide a unique nutritional contribution to the predators’ diets. Future studies will compare the nutritional value of different prey species, and will look at what other prey items are being consumed by these predators in potato fields.