Stink bugs are common in soybeans after bloom, but as of yet, rarely cause severe economic damage in the northern states - Photo: R. Ottens, University of Georgia.
There are three species of stink bugs common in northern soybeans: the green stink bug (Acrosternum hilare), brown stink bug (Euschistus servus), and the spined soldier bug (Podisus maculiventris). Several other species of stink bug are found in southern states and may be moving north. These include the red-shouldered stink bug, the red-banded stink bug, and most recently, the brown marmorated stink bug, an invasive species introduced from Asia and making its way across the continent.
Stink bugs are relatively large insects, from 1/2 to 1-inch long as adults, with a characteristic "shield" shape. Stink bugs are attracted to soybean plants in the bloom to early pod-fill stages and use their piercing and sucking mouthparts to feed on developing seed
Green stink bug adults are easily identified as large, bright green insects with black bands on their antennae. Nymphs are multicolored (black/green, and yellow or red), and rounder in shape, similar to a beetle.
Brown stink bugs are brown on the upper side, and yellow to light-green on the underside during summer. Nymphs are copper-brown.
The spined soldier bug is a beneficial insect that preys on pest insects, especially larval forms of pest caterpillars and beetles. Spined soldier bugs are also brown on the upper side, but have more pronounced and pointed “shoulders”, a black spot on the abdomen, reddish legs and are cream-colored on the underside.
Brown stink bug nymph (left) and adult (right) - Photo: M. Rice, Iowa State University - Click on image to view a larger version.
Green stink bug nymph (left) and adult (right) - Photo: M. Rice, Iowa State University - Click on image to view a larger version.
Immature stink bugs are called nymphs, and look similar to adults
Photo: University of illinois Extension
Both nymphs and adults are attracted to developing seed in maturing soybean fields. They will also feed on soybean stems, foliage and flowers. Direct feeding mainly reduces soybean quality. Young seed can become deformed or remain undersized; older seed discolored or shriveled. The feeding wound provides an entry for secondary diseases, and affected seed more likely to deteriorate in storage.
Stink bugs prefer soybean, but will also feed on developing fruit, fruit trees, corn and other crops. Stink bugs cannot clip silks in corn, however, as they do not have chewing mouthparts.
Stink bugs overwinter as adults or older nymphs in protected wooded areas beneath leaf litter or logs. Most stink bugs in the upper midwest have probably migrated from overwintering sites further south. Stink bugs go through a simple metamorphosis with egg, nymph, and adult stages.After hatching, the wingless nymphs molt several times before becoming full-sized, winged adults. There is usually one generation per year in the north.
During early summer, stink bugs feed on berries, pods, and seeds in uncultivated, wooded areas, and move to crops as seed and fruit mature.
Spined soldier bug nymph Photo credit: R. Ottens, Univ. of Georgia
Because female stink bugs are highly attracted to the soybean plant once it starts to bloom, sampling should begin at that time. Counts the number of older nymphs (larger than 1/4 inch) as well as the adults.
Use sweep nets or shake plants over a drop cloth. Sweeps are more appropriate for drilled, narrow row beans. A “shake sample” to dislodge bugs from the canopy on to a light colored cloth placed between rows is suitable for wide row beans.
Stink bugs aggregate, and it’s more common to find them at field edges or in groups on plants in localized spots, rather than in the middle of a field or distributed throughout a field. Therefore, check 5 different areas of the field; for example, 20 sweep net samples at each of 5 locations. Calculate stinkbugs per sweep (or per row foot) based on the whole field, and not an infested clump at one field edge or corner.
Stink bug thresholds range from 1 to 3 bugs per foot of row as soybean pods begin to fill. Check with your state Extension entomologist for the recommended threshold in your area. Because stink bugs usually reduce quality more than they do quantity; soybean grading standards are helpful to determine the need for rescue insecticide treatments. Thresholds would also be higher for seed beans than grain soybean.
Stink bug populations are partially suppressed by predators and parasitic wasps. The egg parasitoid Telenomus podisi is a common parasitoid that can significantly reduce the number of stink bug eggs in a field. Parasitized stink bug eggs are typically darker than nonparasitized ones.