Comparing the consumptive and non-consumptive effects of a native and introduced lady beetle on pea aphids (Acyrthosiphon pisum)

Abstract

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 (C. septempunctata), on the ability of the coccinellid complex to control pest aphids. Specifically, we compared the consumptive and non-consumptive effect of each coccinellid species on aphids. The consumptive effect was measured by determining the functional responses for each lady beetle and calculating attack rate, handling time, and maximum feeding rate on a shared prey item, the pea aphid (Acyrthosiphon pisum). Non-consumptive effects were examined by assessing pea aphid dropping rates in response to foraging by the coccinellids on fava bean plants. Our results indicate that C. septempunctata has both a significantly greater consumptive effect and non-consumptive effect on A. pisum than C. novemnotata. Modeling indicates that C. septempunctata should 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.