Natural Enemies of Cereal Aphids in Michigan Wheat: Aphid Suppression and Relative Importance of Ground-dwelling and Foliar -foraging Predators

Natural enemies (predators and parasitoids) are effective biological control agents which can suppress pest populations in many crops. We conducted two independent studies in 2012 and 2013 to quantify the impact natural enemies have on cereal aphid population growth in winter wheat (Triticum aestivum L.). Experiments were conducted in four fields on the Michigan State University campus farm in East Lansing, Michigan. Wheat plants were infested with Rhopalosiphum padi (L.) and Sitobion avenae (F.) (Hemiptera: Aphidae). Mesh cages were used to exclude natural enemies and open plots without any barriers were used as a control. For our first study we investigated the role of the entire natural enemy community (foliar-foraging and ground-dwelling predators) on aphid population growth. We found that the natural enemy community was very effective at suppressing cereal aphid population growth in our fields. For our second study we investigated the relative role of each natural enemy feeding guild (foliar-foraging versus ground-dwelling predators) independently. Results from our second study showed significantly greater cereal aphid densities in plots where ground-dwelling predators were excluded compared to plots where foliar-foraging predators were excluded. This suggests that in our system ground-dwelling predators are more important than foliar-foraging predators in keeping aphid populations below critical thresholds. Overall, the results from both studies confirm that the natural enemy community in Michigan wheat fields can effectively suppress cereal aphid population growth.

Keywords: Natural enemies, foliar-foraging predators, ground-dwelling predators, cereal aphids.