Green stink bugs are being found in soybean near Ames but their populations are relatively small and I do not expect economic damage to occur. It would not be unusual to find them throughout at least the southern half of Iowa, especially because many people are in their fields looking for soybean aphids. This insect occasionally is a problem in Illinois. Mike Gray, extension entomologist at the University of Illinois, provides the following information on stink bug biology and treatment considerations.

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Green stink bug.

Many field observers tend to overlook stink bugs and the potential injury they can cause, even though they may be the most important pod feeders in Illinois. Watching for stink bugs, especially in the southern half of the state, should be a high priority for soybean producers.

Green stink bugs are thought to migrate northward from overwintering sites (wooded areas beneath leaf litter) as adults. During early summer, the adults feed on berries in trees, especially dogwoods. Stink bugs are first found in soybean fields during August. They undergo incomplete metamorphosis (immature bugs resemble the adults), which requires approximately 45 days from nymphal hatch to adult emergence. There is usually only one generation of green stink bugs per year in Illinois.

Immature stink bugs (nymphs) have a flashy display of black, green, and yellow or red, and short, stubby, nonfunctional wing pads. The adults are large (approximately 5/8 inch in length), light green, and shield-shaped with fully developed wings. Both adults and nymphs have piercing and sucking mouthparts for removing plant fluids. Stink bugs feed directly on pods and seeds; however, their injury is difficult to assess because their mouthparts leave no obvious feeding scars. Stink bugs use their mouthparts to penetrate pods and puncture the developing seeds. They inject digestive enzymes into seeds, and the feeding wound provides an avenue for diseases to gain entry into the pod. Seed quality also is reduced by stink bug feeding, and beans are more likely to deteriorate in storage. An insecticide application for control of stink bugs may be warranted when the level of infestation reaches one adult bug or large nymph per foot of row during pod fill. Penncap-M is labeled for control of stink bugs at 1-3 pints of product per acre. Do not apply within 20 days of harvest.