August 10, 2010

Reports of stink bugs in Nebraska corn and soybean have been increasing the last few years. In the past, stink bugs have not been considered a significant pest of corn or soybean in Nebraska, but they are economic pests to a variety of crops in the southern United States.

Over the last five to ten years there appears to be a general trend of increasing stink bug populations in more northern states, including Nebraska. Because stink bugs were only an occasional pest in seedling corn in Nebraska, we do not have well researched stink bug management recommendations. Therefore, the Nebraska Soybean Board funded a study to assess the damage potential for stink bugs in Nebraska and to develop a stink bug integrated pest management program.

Nebraska Stink Bugs

The major stink bug species in Nebraska are the brown stink bug (Euschistus servis, Figure 1), the one-spotted stink bug (Euschistus variolarius), and the green stink bug (Acrosternum hilare, Figure 2). In general, adult green stink bugs are bright green, and adult brown stink bugs are brown with a yellow or light green underside. Green stink bug nymphs change color and pattern as they grow, but brown stink bug nymphs are yellow to tan with brown spots down the center of the abdomen. The onespotted stink bug looks similar to the brown stink bug, except it has a small spot on the underside of the abdomen.

Recent surveys (2009-2010) indicate several other economically important stink bug species are present in Nebraska. These include redshouldered stink bugs (Thyanta, Figure 3) and dormant stink bugs (Holcostethus limbolarius). In addition, the spined soldier bug (Podisus maculiventrus) has been collected. This is a beneficial insect predator. Ongoing studies will determine how important these species are to Nebraska crops.

General Biology

Adult stink bugs overwinter primarily in leaf litter, under bark, or in wood piles. We believe that the green stink bug migrates north. We typically begin to find the green stink bug in July. Brown and one-spotted stinkbugs, as well as the other recently collected species, appear to overwinter in Nebraska.

In the spring, adult stink bugs leave the overwintering sites and feed on a variety of wild and cultivated hosts. Early spring sampling indicates brown and one spotted stink bugs prevalent in alfalfa and wheat. After feeding a few days, stink bugs mate and lay clusters of eggs. As the season progresses, female stink bugs are attracted to a variety of flowering plants, including corn and soybean. There are likely one to two generations in Nebraska, depending on species.

Stink Bug Injury

Stink bugs have piercing and sucking mouthparts and feed by piercing a plant part (or another insect in the case of the spined soldier bug), injecting digestive enzymes, and removing fluids.

Nymphs and adult stink bugs injure reproductive stage corn by piercing the husk and feeding on the developing kernels from the beginning of kernel formation through milk stage, although they can feed through the hard dough stage. Damage appears as missing or shrunken kernels. Severe damage causes ears to curve (banana ears). ( Also see the May 7, 2010 CropWatch article, Scouting for and Treating Stink Bugs on Seedling Corn).

Nymphs and adult stink bugs injure soybeans by puncturing various soybean plant parts and extracting plant fluids. They prefer young tender growth and developing seeds. As they feed they inject digestive enzymes, which cause deformation and abortion of seeds and pods, and predispose the feeding site to various pathogens. In addition, stink bugs can cause delayed maturity and deformed leaf growth. Yield and quality losses depend on when the bugs injure soybean, and can be severe.

Injury in either corn or soybean often appears first on field borders as the stink bugs move into the field. With time the stink bugs can move throughout the field.

Stink Bug Management

In general, thresholds are based on counts of large nymphs and adults, as those are the most damaging stages. Green stink bugs are more numerous in soybeans and brown stink bugs more numerous in corn, but don’t be surprised to find a mix of species.

For Soybeans

Thresholds for stink bugs on soybeans vary considerably by state, and also do not explicitly consider variable costs of control or market value. They range from 0.3 per ft-row (Illinois) to 3 per ft-row (Wisconsin), or 0.2 per sweep (Indiana) to 6 per sweep (Ohio) and are not consistent with respect to timing, row spacing, or soybean use (seed or grain). The most common threshold for stink bug in soybeans is 1per row-ft during the reproductive stages. If thresholds are met, the standard insecticides registered for soybean should be effective.

For Field Corn

Florida recommends that “for corn in the early silk through milk stage, treatment may be justified when there is 1 stink bug per 5 plants. From the end of milk through the hard dough stages treatment may be justified when there is an average of 1 stink bug per plant. Only stink bugs 1/4 inch or longer should be considered when determining thresholds.”

Georgia advises that “corn is most sensitive to stink bug injury during ear elongation before pollen shed. The treatment threshold at this stage is one bug per four plants (25% infested plants). Once pollination occurs, feeding through the husk causes damage to individual kernels. Kernels are susceptible to damage up until the milk stage (R3) and possibly early dough stage (R4). The threshold at this time is one bug per two plants (50% infested plants).”

Tom Hunt, Extension Entomologist, NEREC Haskell Ag Lab, Concord
Bob Wright, Extension Entomologist, UNL Entomology Department, Lincoln
Keith Jarvi, IPM Assistant, NEREC, Norfolk