Mutualistic and antagonistic trophic interactions in canola: The role of aphids in shaping pest and predator populations

Aphids have important effects on the abundance and occurrence of tending ants, predators, and pests in agronomic systems, and DNA-based gut content analysis can aid in establishing predator-prey interactions. The purpose of this study was to determine how the presence of aphids, ants, and pest individuals interact within canola (syn. oilseed rape) fields. Using seasonal data from canola fields, the relationships among ants, aphids and pest individuals were determined, along with the use of PCR techniques in order to amplify aphid DNA and confirm food web links on predators who consume aphids. We determined that aphid presence positively influences the number of ants and predators in a community, and diminishing aphid populations over the growing season were associated with declines in both ants and predators. These reduced populations of predators and aphids may have provided the opportunity for a key pest, Pieris rapae to build populations as the season ensued. This research suggests that complex interactions among herbivores and shared predators contribute to pest outbreaks.