Stink bug

John Van Duyn, North Carolina State University, Entomology Extension Specialist

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Stink bugs are important late season insect pests of the soybean seed and reduce both yield and quality by their feeding. Although "grain soybeans" are affected by stink bug, "seed soybeans" and "vegetable soybeans" are more vulnerable in terms of severity and frequency of loss. Stink bugs have piercing mouth parts and feed on tender terminals, blooms, pods, and developing seeds within pods. When feeding, both adults and nymphs (immatures) inject a digestive saliva into the plant which helps liquify plant tissues for easy extraction by the bug. The salivary fluid causes direct tissue damage and also can carry yeast organisms that grow within the seeds. Feeding may also create an avenue for pathogen entry into the plant. Germination and general seed quality can be affected by stink bug feeding. Additionally, feeding injury during early seed formation can result in aborted seeds and undersized, deformed seeds.

These shield-shaped bugs can be found in fields across the state but usually do not reach pest levels in areas outside of the mid and southern coastal counties and adjoining areas. Three kinds of stink bugs may become abundant in soybean, the green stink bug, southern green stink bug, and brown stink bug. Of the three species, the southern green stink bug has the greatest damage potential. However, overwintering southern green stink bugs are affected by cold weather and seldom become a problem in seasons following winters with temperature periods in the teens. The green and brown stink bugs are more cold hardy and are present each year. A single species is seldom a problem individually, but as a complex of stink bugs, they may reach damaging levels. Stink bugs affect fruiting soybeans and reach peak populations in late August through early October, primarily in mid-September. They may be active until frost.

Both the adult and immature (nymphs) stink bugs are found in soybean fields. Stink bugs are highly attracted to fruiting soybeans and colonization of fields is influenced by planting date and cultivar maturity. At our latitude, there appears to be two to three generations (depending on the season and location) and damaging populations usually do not occur until at least late August. Nymphal stink bugs are not very mobile and remain in the vicinity of the egg cluster through the third growth stage (for about 2 weeks). However, the larger nymphs (fourth and fifth instars) and the adults are more mobile. Small stink bug nymphs may be mostly black (southern green stink bug), reddish brown to pale green with black and white stripes on the abdomen (green stink bug), or pale yellow to tan with brown spots (brown stink bug). Large nymphs (last two stages) are pale green with pink, black, and white markings (southern green stink bug); green with yellow and black markings or yellow with black markings (green stink bug); or dull yellow/tan (brown stink bug). Adults are green/yellow green with red bands on the antennae (southern green stink bug), bright green with black bands on the antennae (green stink bug), or brown with a yellow underside (brown stink bug). The brown stink bug looks similar to a predatory stink bug, the spined soldier bug, but has rounded shoulders whereas the soldier bug has sharp, pointed shoulders.

Stink bugs often occur in an uneven distribution within soybean fields. Adults move into fields from the edges and, therefore, may be more numerous along the margins during a colonization period. Eggs are laid in masses and after hatching the young nymphs remain in the same area until reaching an intermediate growth stage. Because of this clumping, individual scouting samples may give artificially high, or low, counts of small stink bugs, but these samples may not reflect the general stink bug population in the field. As stink bugs develop into larger nymphs and adults, they move throughout the field. Adult stink bugs are strong fliers and will move to soybeans of differing maturities as they enter the bloom/pod fill period.

Management of stink bugs relies on scouting and thresholds to identify where and when treatment is necessary, and the use of insecticides. Both of the green stink bug species are relatively easily controlled with phosphate and pyrethroid insecticides but the brown stink bug is less easily affected. Brown stink bug should only be treated with phosphate insecticide (e.g. Penncap-M) at higher rates and sometimes this does not give the desired results. Good application technique is very important when attempting to control stink bugs.

Soybean Page

Other Resources

  1. North Carolina Agricultural Chemicals Manual
  2. North Carolina Cooperative Extension Service

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This page (http://www.ces.ncsu.edu/plymouth/pubs/stinkbug.html) was created by John W. Van Duyn Ph D. Extension Entomologist, Wayne Modlin, Res. Tech. III.

Date Created 2/22/00.
Last revised on 2/05/04.

Published by North Carolina Cooperative Extension Service

Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

CAUTION: The information and recommendations in these Notes were developed for North Carolina conditions and may not apply elsewhere.