Brown Stink Bug
Appearance and Life History
Stink bugs are pests of many crops throughout the world. In the United States, plant feeding stink bugs are most often associated with soybean, tobacco, peaches, crucifers, tomatoes, small grains, red clover, and cotton. They are also known to feed on a host of weed species. Their occurrence in corn has been documented, however, little is known of the true impact of this insect on corn.
There are several species of brown stink bugs that may attack corn. The species that has most often been noted in Indiana is the one spotted stink bug, Euschistus variolarius. This stink bug is brown and approximately 7/16 inch (9 mm) in length when full grown. Adults are broad, somewhat flat, and shield-shaped. The area immediately behind the head, the pronotum, is sharply pointed at the sides and often orange-tipped. The underside of the body is pale green to yellowish. Males of this species have a distinct dark spot near the tip of the underside of the abdomen. Nymphs are similar in appearance to the adults, however they are smaller and do not have fully developed wings. As the nymphs develop, wing pads become evident. Other species of brown stink bugs, such as Euschistus servus and Euschistus euschistoides, are similar in appearance. A predaceous species of stink bug, Podisus maculiventris, looks very similar to these species. However, this species has a faint smudge of dark color in the clear portion of the wing and several pairs of dark spots on the femora, or "thigh", of the rear legs.
The one-spotted stink bug overwinters in the adult stage in wooded areas, grass bordering cultivated crops, cover crops, and/or in small grain fields. There is one generation per year. Mating occurs in the spring and eggs are laid after a preoviposition period of approximately 27 days. The total time for development from egg to adult is approximately 56 days. Both overwintered adults and nymphs have been observed in corn. Movement to corn most often occurs when small grains mature or when cover crops or weeds are treated with herbicides or removed for corn planting.
Stink bugs feed by sticking their tubular mouth parts into the plant tissue and suck the plant juices. They inject an enzyme into the plant which helps digest the plant tissue. The plant tissue at or near the feeding site will show some form of injury. This could result in partial destruction of the plant tissue or plant deformity, such as irregular twisting or growth of the stalk. Plant damage is most evident after approximately plant growth stage V5. These plants will often have round to elongated holes in the rapidly expanding leaves. These holes can vary somewhat in size. The holes are often ringed with plant tissue that has turned yellow, the edge of the hole is generally transparent. Although these holes may appear to have been caused by a chewing insect, closer examination reveals that they have been caused by a piercing of the leaf while it was small and rolled up in the stalk or whorl. The holes get larger as the leaf expands. The holes are similar to those caused by billbugs, however, leaf tissue has not been removed by chewing on the leaf.
Other above ground symptoms often observed include suckering (tillering) and other forms of growth deformity. In some cases the plants may split open, leaving a ragged brown slit in the side of the stalk. A jelly-like substance produced by the plant may be evident in the damaged area. Plant dissections often reveal that the growing point has been injured or killed. The damage appears to be most serious in small plants.
Late whorl stage plants are fed on below the leaf through the leaf sheath. This feeding has been reported to sometimes cause injury to the leaf sheath and developing ear behind the sheath. As the ears emerge the bugs shift their feeding activity to the lower outside portion of the ear. Feeding in this area may cause abortion of individual kernels at the feeding site. Since feeding occurs on only one side of the ear, the ear could curve away from the stalk as it grows. Damage, in the form of discoloration, is usually apparent on the shuck surrounding the ear. Although damage to late whorl stage corn or plants in the silking stage can be serious, it is unlikely that economic levels of damage occur very often at this plant stage in the Midwest.
If brown stink bugs or their damage are found in corn, evaluate 20 consecutive plants, beginning with a randomly selected plant in each of 5 areas of a field. In corn, from emergence to mid whorl, record the percentage of plants showing damage.
Note the severity of the damage:
- plants with holes in leaves
- evidence of plant deformity
- slits in the stalk
- dead or dying plants
Also, determine if the bugs are still present. Note if they are at ground level, on stalks, or in whorls. In corn, from late whorl through silking, record the percentage of plants showing stink bug feeding damage, either on leaf, ear sheaths, or developing ears, and note the level of infestation.
Corn Insect Control Recommendations: E-series 219-W (PDF)
Early planting should help reduce the potential for damage. The sooner corn is established, the less chance there is for stink bugs to cause significant damage. This is even the case where corn is no-tilled into a winter cover crop. However, where planting is delayed, especially in no-till situations, stink bugs can be a problem. In this situation, there is very little time to observe stink bug feeding before a control is needed. It is important to remember that spiking corn plants are most vulnerable to attack and damage, especially when seed slots are not closed properly at planting (i.e., soil too wet).
The necessary precautions for managing this pest must be adopted prior to crop emergence. Regular field scouting before planting or crop emergence is recommended. If stink bugs are noted and a burn down herbicide will be used to kill the vegetation within a field prior to planting, the use of a herbicide-insecticide tank mix may be advisable (check labels for specific recommendations and compatibility information). A field can be made less attractive or suitable for stink bugs by tilling the field, thus eliminating the plant cover that can harbor the bugs. If in no-till, closure of the seed slot is absolutely essential in order to prevent the bugs from feeding below ground on the growing point of seedlings.
If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.