Consumptive and non-consumptive effects on pea aphids, Anthrosiphon pisum, by native and invasive lady beetles

While the importation and release of foreign natural enemies in classical biological control programs can be cost-effective, the released control agent can have unintended effects, such as the displacement of native natural enemies. In this study we examined the effect of the replacement of a native coccinellid, the nine-spotted lady beetle (Coccinella novemnotata) by an exotic biological control agent, the seven-spotted lady beetle (Coccinella septempunctata) on the ability of the coccinellid complex to control pest aphids. Specifically, we compared the consumptive and non-consumptive effect of each species. The consumptive effect was measured by analyzing functional responses and calculating attack rate, handling time, and maximum feeding rate and non-consumptive effects were examined by assessing the dropping rates of a shared prey item, the pea aphid (Acyrthosiphon pisum).  Our results indicate that C. septempunctata has both a significantly greater consumptive effect and non-consumptive effect on A. pisum than C. novemnotata.  Further modeling indicates that C. septempunctata will potentially have a greater impact on A. pisum populations but that its greater predatory efficiency could also lead to decreased stability in the interactions between predator and prey populations.