No. 7 Article 7/May 12, 2006

Survey of Buckthorn Reveals Low Soybean Aphid Overwintering Densities

In early May, two seasoned entomologists, David Voegtlin, Illinois Natural History Survey, and Bob O'Neil, Purdue University, spent four days and 1,300 miles looking for overwintering populations of soybean aphid in Indiana, Michigan, and Ohio. They carefully examined thousands of leaves of known hosts (Rhamnus alnifolia, alder-leaf buckthorn; and Rhamnus cathartica, common buckthorn). In addition, they searched for soybean aphids on suspected hosts (Frangula alnus, glossy buckthorn; and Rhamnus caroliniana, Carolina buckthorn). They were unable to find any soybean aphids on alder-leaf buckthorn, glossy buckthorn, or Carolina buckthorn. Two colonies of soybean aphids were found on common buckthorn near Bronson, Michigan (located near the Indiana and Michigan border). Infestations of soybean aphids in Michigan reached impressive levels last year, with an estimated 80% of soybean acres receiving an insecticide application.

David Voegtlin coordinated the establishment of the soybean aphid suction trap network throughout the North Central Region and continues to interpret the predictive potential of these data collected each season. David indicates that the 2005 fall flight of soybean aphids in Illinois was greater than fall flights in 2001 and 2003. However, he also noted that the 2005 flight was approximately half of the 2002 and 2004 flights, both of which were followed by more impressive infestations the subsequent growing seasons. Of particular interest is David's observation that the number of male soybean aphids in the fall flight of 2005 was very low. This observation was common among the cooperators participating in the North Central Region suction trap network. In 2005, the greatest captures of fall migrants occurred in Iowa and Minnesota. If economic infestations develop, David anticipates that we are most likely to see them develop first in these areas of the Midwest. In other areas of the North Central Region, economic levels of soybean aphids may not develop until much later in the growing season. Time will tell. We thank David Voegtlin and Bob O'Neil for sharing the results of their survey efforts!--Mike Gray

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