Department of Crop Sciences University of Illinois at Urbana-Champaign

Agronomy Day 2006

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50 Years of Invasive Insect Pests: Managing Soybean Aphids, a New Foe

Kevin Steffey Kevin L. Steffey
Professor and Extension Entomology Specialist
Department of Crop Sciences
ksteffey@illinois.edu
217-333-6652

Invasive insects in soybean production systems in Illinois are few. Although only two invasive species regularly concern soybean growers in Illinois, those two species are “whoppers”—Japanese beetle and soybean aphid. Japanese beetles have threatened soybean in some areas of the state for decades, and attempts to control them are legendary. However, no insect has had such a dramatic annual impact on soybean production as the soybean aphid.

figure 1

Soybean aphids
(photo courtesy of Gary Bretthauer)

First discovered in the United States in August 2000, the soybean aphid has since spread rapidly throughout the major soybean-growing states in the Midwest, into Canada, and to the East Coast. The impact of the soybean aphid on soybean yields is not consistent every year, especially in Illinois (i.e., soybean aphid populations reach economic levels more frequently in the relatively cooler, northern Midwestern states). However, in 2003 when soybean aphid densities reached outbreak levels in many states, millions of acres were sprayed with insecticides, and estimates of yield losses were exorbitant. Since then, soybean associations, including the Illinois Soybean Association, have invested funds to support research to improve management strategies for the soybean aphid.

The presence of soybean aphids in the United States has changed the way we perceive and practice soybean insect management. Many producers and agribusiness professionals have responded to the threat of soybean aphids in much the same manner that people have responded to the threat of corn rootworms in corn. To produce a crop for which insect control costs were mostly insignificant in the 20th Century, many producers now expect to spend money annually for insect control. Some soybean producers seek prophylactic solutions or enact knee-jerk responses to anticipated insect threats. Consequently, considerable soybean aphid research is designed to determine best management practices, considering both economic and ecological impacts of soybean aphid control.

figure 2

Japanese beetle
(photo courtesy of Ron Hines)

Among the most important early, practical findings from soybean aphid research was development of an economic threshold that has been adopted throughout the Midwest—250 soybean aphids per plant, with 80% of the plants infested. Follow-up research has verified the conservative nature of this threshold, i.e., economic losses usually do not occur until densities reach 1,000 soybean aphids per plant (economic injury level). Because the economic threshold is lower than the economic injury level, soybean producers have time to react before economic losses occur.

Other funded areas of soybean aphid research include: (1) efficacy of foliar- and seed-applied insecticides; (2) efficacy of soybean germplasm that is resistant to soybean aphids; (3) impact of predators (e.g., insidious flower bug, multicolored Asian lady beetle) on soybean aphid populations; and (4) importation of natural enemies of soybean aphids from Asia, and their impact on soybean aphid populations. In addition, sampling efforts are underway to refine information about the population dynamics of soybean aphids in several Midwestern states, with some hope of being able to forecast soybean aphid outbreaks.

Ultimately, the combined research efforts of entomologists throughout the Midwest should result in a comprehensive, multi-tactic, and effective program of soybean aphid management with minimal impacts in the environment. Results from research efforts in 2006, if relevant, will be discussed.