Factors facilitating synergistic predation: The central role of synchrony

Determining the phenological and diel concurrence of potentially overlappin g predator guilds in a given system provides a gauge of the potential preva lence and importance of synergistic prey suppression. The phenology of pea, aphids (Acyrthosiphon pisum) and ground- and foliar-foraging predators was determined through a combination of pitfall and sweep-net sampling in alfa lfa. These results revealed diverse guilds of ground-and foliar-foraging pr edators with a high degree of phenological overlap among individual species . One of the most common ground-foraging predators, Harpalus pennsylvanicus , was found to be significantly more active at night, but also to maintain moderate activity levels during the day. When tested individually in simple arenas with full access to aphids, the aphid-consumption rates of five com mon ground-foraging predators (H. aeneus, H. pennsylvanicus, Amara familiar is, A. octopunctatum, and Philonthus spp.) were not significantly different from that of Coccinella septempunctata, a foliar-foraging predator that is held to be one of the most important aphid consumers in alfalfa. Thus, bot h the seasonal occurrence and daily activity levels of these two aphid pred ator guilds overlap, and the ground-foraging predators, which are often ove rlooked as sources of aphid predation, were shown to be effective aphid con sumers. Three key elements emerge from the alfalfa-aphid-predator system as general predictors of the probability for the synergistic predation on pests by me mbers of a predator complex: (1) synchrony of predator species in the compl ex, (2) predator-induced escape behavior of prey resulting in habitat switc hing and encounter with a new predator guild, and (3) minimal negative inte raction (intraguild predation or interference) between the predator species . These elements can aid in identifying systems where the conservation or a ugmentation of ground-foraging predators or other interactive predator guil ds will be most effective.