(From left to right) Lady beetle eggs, compared to the size of a penny, lady beetle larvae feeding on soybean aphids, and adult Asian lady beetle. (Photos courtesy of Dr. Chris DiFonzo, Michigan State University. )

June 30, 2006

When managing soybean aphids

Preserve natural enemy populations

Minute pirate bug nymph

Understanding how natural enemies impact aphid populations is an important component of developing a comprehensive management plan. That’s why the Nebraska Soybean Board funded a project at UNL’s Haskell Agricultural Laboratory at Concord to examine the effects of predators and parasitoids on soybean aphid populations. Tierney Brosius, a UNL entomology graduate student, was placed in charge of this project and has discovered some interesting relationships that add to our understanding of the soybean aphid in Nebraska.

For one thing, although the most visible soybean aphid predator is the Asian lady beetle, the minute pirate bug (Orius insidiosus) is the most commonly occurring predator. This is a common predator throughout Nebraska that feeds on a variety of small insects and spider mites. The study indicates that naturally occurring predators, primarily the minute pirate bug, can significantly slow soybean aphid population growth, and that initial populations of predators may reduce the rate of successful colonization of the soybean aphid. In addition, the presence of minute pirate bugs causes the aphid population to be distributed throughout the canopy, with a higher proportion lower in the canopy than in soybeans without significant levels of minute pirate bugs.

Also see: Soybean aphids in Nebraska Soybean aphid management

This has important implications for soybean aphid management. Preserve your natural enemy populations. Premature or unneeded insecticide use can rid your soybeans of these important control agents and leave your field open for aphid colonization and rapid population growth. For example, do not add an insecticide to a glysophate application simply to “clean up the field.” This can lead to later problems with the soybean aphid as well as other pests such as the twospotted spider mite. Always remember to treat only when necessary. Aphids must be present with populations growing and reaching economic thresholds. Also, when scouting for aphids, make whole plant aphid counts. A significant number of aphids may be in the middle of the canopy.

Of course, this does not mean we can leave the work to the natural enemies and not scout. When environmental conditions favor soybean aphids, they can overcome the effects of the natural enemies and aphid populations can skyrocket. We will continue to do research to determine the environmental and biological conditions that favor the soybean aphid and its natural enemies.

Tierney Brosius
M.S. Graduate Assistant, UNL Entomology
Tom Hunt
Extension Entomologist
NEREC Haskell Ag Lab, Concord

Copyright 2006 by the University of Nebraska Board of Regents. All rights reserved.

Published by University of Nebraska-Lincoln Extension in the Institute of Agriculture and Natural Resources Cooperating with the counties and the U.S. Department of Agriculture.

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