Predation of green peach aphids by generalist predators in the presence of alternative, Colorado potato beetle egg prey

In Washington State two insect herbivores commonly co-occur on potato (Solanum tuberosum L.), the green peach aphid ("GPA," Myzus persicae Sulzer) and the Colorado potato beetle ("CPB," Leptinotarsa decemlineata Say). Locally, generalist predators dominate the community of natural enemies in potato fields. The presence of multiple prey species might distract generalists from feeding on any single target pest. In the laboratory, we examined whether consumption rates of several predator species on focal (GPA) prey was reduced in the presence of alternative (CPB egg) prey. In initial measurements of predation rates we found that two predator species, Nabis spp. and Geocoris spp. bugs, had the highest consumption rates on aphids, potato beetle eggs and small potato beetle larvae. So, we focused on Nabis spp. and Geocoris spp. in later experiments. In Petri dish arenas Nabis ate significantly more GPA per capita than did Geocoris; both predators exhibited weakly suppressed aphid consumption rates when CPB eggs were also present. However, in experiments in larger greenhouse microcosms including potato plants, this weak disruptive effect of CPB eggs disappeared. Geocoris ate nearly identical numbers of aphids across a 4-fold range of CPB egg density. Nabis, in contrast, ate significantly more aphids when 40 CPB eggs were included in microcosms, compared to microcosms with no alternative prey present. Thus, we would not expect any strong disruption of M. persicae control by Nabis spp. or Geocoris spp. when L. decemlineata eggs are also present in the field.