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Project 8

Project Title: Impact of the landscape structure and intraguild interactions on the biocontrol of soybean aphid, Aphis glycines.
Investigators: Mary Gardiner, Doug Landis, Chris Difonzo, Matt O’Neal, George Heimpel, Claudio Gratton, Nick Schmidt, Emily Mueller, Jeremy Chacon.
Contact: Mary Gardiner (gardin18@msu.edu)

Abstract: The soybean aphid, Aphis glycines Matsumura, a native of Asia, was first detected in the U.S. in 2000.  Its current distribution extends throughout the North-Central U.S. and into Canada.  Within this introduced range landscape structure has critical influences on soybean aphid, its predators, and their interactions in agroecosystems.  The impact of the predator community on soybean aphid population dynamics varied across 12 sites sampled in Michigan, Wisconsin, Minnesota and Iowa. In 4 of the 12 sites, predators had no impact on aphid population growth.  In the remaining 8 sites, predators either delayed (4 sites) or prevented (4 sites) aphid populations from reaching threshold.  We examined the relationship between coccinellid species abundance and the amount of non-crop habitat (woodlots, wetlands, pasturelands, grasslands, and urban areas) in the landscape as well as overall landscape heterogeneity.  Exotic lady beetles (Harmonia axyridis, Hippodamia variegata, and Coccinella septempunctata) were positively correlated with non-crop habitat and habitat heterogeneity.  Native lady beetle populations (Hippodamia convergens, Coleomegilla maculata, Cycloneda munda, and Hippodamia parenthesis) were negatively correlated with habitat heterogeneity; they were most abundant in homogeneous landscapes dominated by corn and soybean.  These findings suggest that native and non-native predators of soybean aphid may be experiencing landscape influences in different ways.
 
In addition to understanding how landscape can influence the structure of a predator community, we also were interested in how interactions between species within a soybean field impacted biocontrol of A. glycines.  Since soybean aphid is attacked by a large guild of predators, intraguild interactions such as intraguild predation may occur, and influence overall aphid suppression.  We examined interactions between the exotic coccinellid Harmonia axyridis, the native gall midge Aphidoletes aphidimyza and the native lacewing Chrysoperla carnea.  We explored the impact of intraguild predation on soybean aphid population dynamics by comparing aphid populations in microcosms with either A. aphidimyza larvae or C. carnea larvae alone, with both a H. axyridis adult and either A. aphidimyza or C. carnea larvae, and without predators.  When H. axyridis was present with larval A. aphidimyza or C. carnea, the lady beetle acted as an intraguild predator.  However, intraguild feeding did not result in a release of aphid populations compared with microcosms containing only the intraguild and aphid prey.  A similar result was found in field cages.  Cages allowing large predators had reduced numbers of A. aphidimyza and C. carnea larvae but also significantly fewer aphids compared with predator exclusion cages. Thus, in both lab and field studies the direct impact of H. axyridis on A. glycines overcame its negative impact as an intraguild predator.
 
For more information: 
Mary Gardiner, gardin18@msu.edu, 517-432-5282