Testing an interference competition hypothesis to explain native lady beetle decline.

Project Investigators: Chelsea Smith and Mary Gardiner

Lady beetles (Coccinellidae) provide valuable biological control services in agricultural settings in Ohio, and throughout the United States. Recent population surveys show a dramatic decline of several native coccinellid species, which coincides with the establishment of exotic coccinellid populations. Interference competition via intraguild predation (IGP) of native coccinellid eggs and larvae by exotic coccinellids has been proposed as a mechanism to explain this decline. I have conducted preliminary testing of this hypothesis measuring levels of egg predation experienced by coccinellids within three focal habitats: alfalfa, soybean, and grassland. The declining native species, Hippodamia convergens, experienced the most predation when compared to the recently established exotic species, Harmonia axyridis, and another native species, Colemegilla maculata, which is not in decline. Given the evidence that declining native coccinellids face elevated egg predation, the next important question to ask is: What actually preys on the egg masses? This research aims to use camera systems to directly observe the community of predators that attack eggs of H. axyridis and H. convergens. This proposed research will also determine how the composition of the surrounding landscape influences IGP and the guild of potential egg predators. Currently, the reason(s) behind the decline of native coccinellids are not understood. This research will greatly advance our understanding of threats to native lady beetle populations, which is a concern for future biological control services, as well as the conservation of an ecosystems biodiversity.

Completed: 2012