Stink Bugs in Corn and Soybeans

Eileen Cullen, Extension Entomologist, UW Entomology Dept.

Stink bugs are making an appearance in corn and soybean fields this late season, in higher numbers than usual, particularly the green stink bug. Both the green stink bug, Acrosternum hilare, and brown stink bugs , Euschistus spp. can be found in fields during August. Green stink bug nymphs and adults have been reported from corn and soybean fields in Langlade, Polk, Clark, Portage and Shawno Counties. You have likely observed them in other locations as well.

Stink bugs are unlikely to cause economic damage to corn and soybeans in the Upper Midwest. In fact there are no damage relationships or economic injury levels established for stink bug on field, seed or processing sweet corn at this late stage in the season. On soybeans, the green stink bug is a key pest (feeding on pods and seeds) and typical economic problem in the southern United States, but rarely in the northern states. Scouting and threshold information are provided below for soybeans.

Feeding Behavior and Field Distribution

• Stink bug nymphs and adults feed with piercing-sucking mouthparts. They seek out seed pods, fruits, grain heads, inserting their needle-like mouthpart, injecting enzymes to dissolve plant tissue, then sucking out “pre-digested” plant fluids.
• Stink bugs cannot clip silks in corn (do not have chewing mouthparts).
• Edges/sides of fields adjacent to wooded habitat are likely spots to find stink bugs, rather than throughout the field or in the middle of the field. (During early summer, stink bugs feed on berries, pods, seed heads in uncultivated, wooded areas).
• Males emit a pheromone which signals to other members of the same stink bug species a call to “clump” together (suitable food, mates, habitat).
• Stink bugs aggregate, and it’s more common to find them on field edges and in groups on plants or spots in field sides/edges – rather than distributed throughout a field, or in the middle of fields. 
• Stink bugs emit a strong odor as a defense mechanism. 

Life History

• Stink bugs overwinter as adults under protected areas like leaf litter, wooded areas, river edge vegetation.
• In the Upper Midwest, stink bugs are thought to migrate northward from overwintering sites in their adult stage. There is usually one generation per year in this region. 

Identification

• Stink bug adults have a shield shaped body, with pointed “shoulders”.
• Green stink bug adults are bright green with black bands on their antennae. Nymphs are multicolored (black/green, and yellow or red), rounder in shape (resembling a “beetle”).
• Brown stink bugs are brown, and nymphs are copper/brown. Stink bug nymphs remain clustered near the egg mass after eclosing, and disperse further after molting to 2^nd instar. Adults are brown on the upper side, and yellow to light-green on the underside during summer.
• The spined soldier bug, Podisus maculiventris, is a beneficial insect – preying on pest insects, especially larval forms of Lepidoptera (pest caterpillars) and Coleoptera (beetles). Spined soldier bugs are also brown on the upper side, but have more pronounced/pointed “shoulders”, a black spot on the abdomen, reddish legs and are cream-colored on the underside.

Green stink bug, Acrosternum hilare, nymph (left) and adult (right). 

Photo Credits/Source: Dr. Marlin Rice,

Prof./Extension Specialist, Iowa State University Entomology Dept.

Feeding and Damage Relationships in Corn and Soybeans

• Monitor several sites in a given soybean field. This is important due to the aggregated field distribution of stink bugs. (You may have a spot of damage near field (edges) but no where else in the field).
• Check 5 different areas of the field (for example, 20 sweep net samples at each of 5 locations).
• Sweep net or drop cloth samples can be used. 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.
• Combine nymphs and adults in sample total. 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. Based on sweep net samples, for grain soybean 0.4 bugs per sweep (40 in 100 sweeps), and for seed beans 0.20 bugs per sweep (20 in 100 sweeps). (while pods are still green).