Brown Stink Bug as a Pest of Corn in the Southeastern United States

There are several pest species of stink bugs found in the southeastern United States, including the green stink bug, Chinavia hilare, the southern green stink bug, Nezara viridula, the rice stink bug, Oebalus pugnax, and brown marmorated stink bug, Halyomorpha halys. One of the most common species is the brown stink bug, Euschistus servus (Say). The brown stink bug is a pest of numerous cultivated crops, including soybean, cotton, and corn. The brown stink bug is a native species in a large portion of the United States and has historically been considered a sporadic pest of many cultivated crops. Due to farm management practices, such as reduced and no tillage, favoring large overwintering populations, and reduced use of broad-spectrum insecticides, the brown stink bug has become a perennial pest in many cases. Field corn is particularly susceptible to injury from brown stink bug, which can occur throughout much of the growing season.

Identification

Eggs of the brown stink bug are cylindrical and laid in clusters of around fourteen to forty-two eggs. Eggs are translucent yellow, and the top of each egg turns pink as it matures (figure 1). The brown stink bug develops through five nymphal stages or instars. Nymphs are similar in appearance to adults, except that they are smaller and lack wings. First instars congregate on the egg mass and begin to disperse as second instars. Early instars are brown to black (figure 2), and as they mature, begin to turn light greenish yellow with some brown on the margins (figure 3). Nymphs of the brown stink bug have a characteristic longitudinal brown patch on the ventral (top) side of the abdomen that can help distinguish it from other similar stink bug species (figure 3). Adult brown stink bugs are brownish-yellow, shield-shaped insects measuring 10-15 mm long and 7-9 mm wide (figure 4). The ventral side (underside) of adults is green initially and slowly turns yellowish-brown as they reach maturity.^1,2

Figure 1. Mature brown stink bug eggs. Image credit: Herb Pilcher, USDA Agricultural Research Service, Bugwood.org.

Figure 2. First instar brown stink bug nymphs. Image credit: Herb Pilcher, USDA Agricultural Research Service, Bugwood.org.

Figure 3. Fifth instar brown stink bug nymph. Image credit: Herb Pilcher, USDA Agricultural Research Service, Bugwood.org.

Figure 4. Brown stink bug adult. Image credit: Herb Pilcher, USDA Agricultural Research Service, Bugwood.org.

Life Cycle

Brown stink bugs overwinter as adults in crop residues, leaves, weeds, and crevices in trees. They produce two to three generations per year and generally are active from April through October. It takes four to five weeks, on average, to complete the life cycle from eggs hatching to a mature adult.² Often, the first generation each year will feed and oviposit in a weedy host or a winter crop host, such as wheat. Manipulation of weedy borders along corn fields has not been found to influence populations of the brown stink bug in corn, suggesting that other hosts, such as wheat or woodlands, are more important overwintering and early season hosts.³ The second generation will migrate into field corn. Migration of brown stink bugs from winter wheat into corn before or during wheat harvest is well documented, and wheat can be a significant source of infestations during susceptible stages of corn development.⁴

Injury to Corn

Stink bugs have piercing-sucking mouthparts and excrete digestive enzymes into plant tissue when feeding. A combination of mechanical injury from inserting mouthparts and physiological injury from digestive enzymes causes injury throughout the season to corn. Corn is susceptible to injury at several stages throughout its development. Descriptions of each growth stage of corn can be found in Ritchie et al. 1986.⁵ From emergence through around the six leaf stage (V6), stink bugs feed directly on the growth point of developing plants and can cause stunting, tillering, and plant death in severe cases (figure 5 and 6).^6–9 Early injury from stink bug feeding ultimately results in yield loss. Several weeks prior to tasseling, during the ear elongation stages of corn, stink bugs feed through the stalk on developing ears, which leads to deformed ears and reduced kernel weight (figure 7). Once the ear emerges, during the first two reproductive stages of development (R1-R2), ears are susceptible to direct kernel injury from stink bug feeding, resulting in discolored or aborted kernels (figure 8).¹⁰ Stink bug feeding during late vegetative and early reproductive stages of can also introduce entry points for fungal contamination, reducing the quality of harvested grain.¹¹

Figure 5. Multiple tillers as a result of stink bug feeding. Image credit: Tim Bryant, Clemson University.

Figure 6. Severe stunting of corn fed on by brown stink bugs. Image credit: Tim Bryant, Clemson University.

Figure 7. Varying degrees of ear deformation as a result of brown stink bug feeding during ear elongation. Image credit: Tim Bryant, Clemson University.

Figure 8. Direct kernel injury from feeding during reproductive corn growth. Image credit: Tim Bryant, Clemson University.

Management

Economic Thresholds and Chemical Management

Brown stink bugs can be controlled with insecticides and, the timing of application and coverage are critical for effective control. Sampling of cornfields should be conducted to determine if brown stink bug infestations are either above (treat) or below (do not treat) economic thresholds, which are one per ten plants from V1 to V6, one per eight plants from V14 to VT, and one per four plants from R1 to R2.

As an alternative to a fixed sampling plan, where a predetermined sample size is chosen (for instance, twenty-five plants in a row at four locations in a field), a sequential sampling plan was developed based on research conducted at North Carolina State University that consists of adjusting sample size based on the number of stink bugs found during initial samples. The advantage of sequential sampling plans is that it can reduce sampling time compared with a fixed sample size.

In addition, scouting time can be reduced by sampling only the areas of the plant where brown stink bugs are most likely to be found.^12,13 When using a sequential sampling plan, one hundred plants are scouted in a given field, and the total number of stink bugs are counted. If the number of bugs exceeds the given number, sampling should cease, and treatments should be applied; if it falls within the lower range, sampling should cease with no treatment applied; and if the number is in the intermediate range, sampling should continue until a decision can be made (table 1).

Table 1. Sequential partial plant sampling plan for brown stink bugs in corn. Sample 100 plants throughout the field, and, if the number of bugs falls within the “Take more samples” range, more samples need to be taken. If the number of bugs detected is below or above this range, stop sampling and follow the recommendation. Only the area described under “Area to sample” needs to be searched to accurately assess the infestation level.¹⁴

When fields reach thresholds, most pyrethroids provide some level of control; however, bifenthrin provides the best control of brown stink bugs.¹⁵ Low residual activity and poor penetration into the canopy can lead to ineffective control in some cases, particularly late in the season.⁴ It is important to use the highest available rate, as well as proper pressure and volume, to allow the insecticide to penetrate the canopy and come into direct contact with target pests.

Several production guides recommend insecticide seed treatments for early season control of stink bugs. Research-based data on the efficacy of seed treatments against brown stink bugs are lacking; however, a large percentage of seed is pre-treated with seed treatments for a range of other pests.

Biological Control

Natural enemies of stink bug eggs have the potential to reduce populations significantly.^16,17 Parasitoids are the primary species attacking stink bug eggs, and in some cases, predation by generalist predators can also be substantial. Telenomus podisi is the primary parasitoid species found in brown stink bug eggs in the Southeast.^16,17 Parasitization rates of eggs generally range from 25% to 90% year to year, with some level of population reduction occurring. Parasitoids are highly susceptible to broad-spectrum insecticides often used for control of brown stink bug¹⁸, emphasizing the need for using insecticides only when populations reach damaging levels.

Summary

The brown stink bug is an increasingly common pest of field corn throughout the majority of the growing season. If left untreated, yield loss and quality reduction of corn grain can occur. Applying insecticide at the proper time (threshold) is the most critical aspect of managing brown stink bugs in corn.

References Cited

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18. Koppel AL, Herbert DA, Kuhar TP, Malone S, Arrington M. Efficacy of selected insecticides against eggs of Euschistus servus and Acrosternum hilare (Hemiptera: Pentatomidae) and the egg parasitoid Telenomus podisi (Hymenoptera: Scelionidae). Journal of Economic Entomology. 2011;104(1):137–142.