Intraguild predator interference of a classical biological control agent of the soybean aphid

An attempt is underway to use a non-native parasitoid wasp to control the invasive pest of soybean crops in North America, the soybean aphid. Successful establishment of Binodoxys communis (the parasitoid) and B. communis' successful control of Aphis glycines (the aphid) may be inhibited if predators interfere with B. communis. My dissertation research examined if and when B. communis is interfered with by predators through a series of field experiments in soybean plots in Minnesota in 2005-2009. First, I studied establishment and predation of a different parasitoid of the soybean aphid in the presence and absence of soybean aphid predators using field cages and found that predators reduced parasitoid reproduction but that the parasitoid still enhanced aphid control. In a second, similar experiment that used B. communis, I found that predators interfered with B. communis reproduction, like in the previous study with the different parasitoid. Unlike the previous study, B. communis did not always enhance aphid control.;After these experiments determined that predators can interfere with B. communis establishment, I tried to determine if predator interference of B. communis is context-dependent. First, I found that predation risk to B. communis pupae on single plants was higher when there were more soybean aphids cohabiting the plant because predators aggregated to plants with many aphids. However, when I released many B. communis into larger soybean plots with high or low aphid densities, predation risk did not depend on aphid density, although B. communis establishment was better at high aphid density. Taken together, the results from my dissertation research suggests that predators will interfere with attempts to establish B. communis, but also that by understanding the relationship between aphid density and predation of parasitoids we may be capable of minimizing predator interference.