Brown Marmorated Stink Bug

(View photos to identify stink bugs)

Brown marmorated stink bug is an invasive pest that was introduced into the eastern United States in the early 2000s. In California, the first established population and damage in agricultural crops were reported in 2016 and 2017 in peach and almond orchards in Stanislaus County. As of 2023, this pest is established in many counties in the northern and central regions of the Central Valley.

The adult brown marmorated stink bug has a shield-shaped body similar to other stink bugs; it is about 0.6 inch (1.5 cm) long and brown with marbled (marmorated) markings. It has distinct white bands on the antennae and legs. Females are slightly larger than males.

Brown marmorated stink bug migrates into orchards from overwintering sites in the spring. Unlike other stink bugs, brown marmorated stink bug adults overwinter in large aggregations in sheltered areas such as buildings, barns, woodpiles, or under the bark of large trees. Within 2 weeks after emergence in spring, overwintering adults mate, and females deposit eggs on host plants. Eggs are round to barrel shaped, white to pale green, and laid on the underside of leaves in clusters, often with 14 to 28 eggs. Nymphs shed their exoskeleton (molt) as they progress through 5 growth stages (nymphal instars) before becoming adults. Nymphs range in size from 0.1 inch (2.5 mm) during the first instar to just under 0.5 inch (12 mm) during the fifth instar.

The newly hatched nymph has an orange abdomen with dark brown plates and a brown head and thorax. First instars remain clustered around the egg cases, feeding from the egg before dispersing, sometimes remaining until they molt to the second instar. The newly molted second instar has an almost black appearance and resembles a tick. Subsequent instars (third through fifth) have a marbled brown head and thorax and reddish-brown, black, and white abdominal markings. Like other stink bugs, fourth and fifth instar nymphs have visible wing pads. Newly molted adults may be white. Peach is a preferred host, and brown marmorated stink bug can complete its entire life cycle in peach.

Do not confuse pest stink bugs with rough stink bugs (Brochymena sulcata and other Brochymena spp.), predators that are speckled white and gray and can also be found in peach orchards. Nymphs of rough stink bugs can be brown mixed with red or white patterns. The most effective way to distinguish nymphs of rough stink bugs from brown marmorated stink bug nymphs is to look for the two white bands on the antennae that identify the brown marmorated stink bug.

For more information on identifying brown marmorated stink bug, see the University of California Integrated Pest Management video, Brown Marmorated Stink Bug (BMSB): Identification and Monitoring in Almond Orchards.

Damage by brown marmorated stink bug is indistinguishable from damage by other stink bugs. However, brown marmorated stink bug may reach very high numbers, with multiple individuals present on a single fruit. Because one bug can feed on many fruits, losses can be severe. Brown marmorated stink bug may be present all season, including in early spring, resulting in a high risk of damage throughout the season. By contrast, native stink bugs cause damage midseason or late season.

Like other stink bugs, brown marmorated stink bug inserts its needlelike mouthparts into fruit and feeds on plant juices. Both adults and nymphs can feed on fruit, but adults and later stages of nymphs cause the most damage. Feeding damage on young fruit may appear as oozing sap. As the fruit expands, it ultimately becomes dimpled or distorted. Internal feeding damage ranges from simple brown discoloration underneath the skin to cork-like flesh and necrosis. Any such feeding damage makes fruit unmarketable.

Brown marmorated stink bug can feed on more than 170 plant species and often moves between noncultivated hosts and agricultural crops. Because of this pest’s ability to feed on a large variety of food sources, brown marmorated stink bug numbers can quickly increase and consequently lead to more crop damage. Brown marmorated stink bug enters orchards from nearby woodlots, residential host plants, and overwintering structures. Orchard edges, therefore, are at the greatest risk for crop damage. Monitoring brown marmorated stink bug by using pheromone-baited traps and conducting beating tray sampling and visual searches is essential for effective management. If this insect is detected in peach orchards in the early season, targeted pest management can begin as early as March and continue through September in some late-season peach varieties.

Several generalist arthropod predators may provide biological control by attacking this pest and its eggs. Trachelas spp. are common egg predators in California urban settings. However, this spider damages only a few eggs with each visit. Other predators include assassin bugs, ground beetles, lady beetles, jumping spiders, praying mantises, earwigs, damsel bugs, and some species of crickets and katydids. These predators have been reported to attack native stink bugs as well as brown marmorated stink bug in various regions of the United States, but their impact in reducing brown marmorated stink bug densities is minimal.

Several species of native wasps parasitize the eggs of native stink bugs. However, these wasps do not frequently parasitize brown marmorated stink bug eggs, so they do not significantly reduce this stink bug’s abundance. These native parasitoids, therefore, may not provide adequate control to minimize the economic loss in commercial peach orchards.

In 2018, a brown marmorated stink bug–specific egg parasitoid from Asia, Trissolcus japonicus, was detected in Los Angeles County. Surveys from China (part of this parasitoid’s native home range) indicate that T. japonicus can provide effective biological control for this pest. Lab and field studies in North America show promise for targeted biological control because this parasitoid has a limited ecological host range with a strong preference for brown marmorated stink bug eggs. University of California Cooperative Extension and the California Department of Food and Agriculture are leading an effort to release this parasitoid in orchards on a small scale for research purposes. However, this parasitoid’s actual impact on brown marmorated stink bug in orchard systems throughout California has yet to be evaluated.

Remove potential overwintering sites and alternate hosts, such as tree of heaven (Ailanthus altissima) and lima bean, which support brown marmorated stink bug populations throughout the season and can serve as a source of orchard infestations. See StopBMSB for a detailed list of plant hosts.

Use biological and cultural controls in an organic production system. Protectants such as kaolin clay may help to reduce fruit damage when fruit is thoroughly covered. Insecticides containing active ingredients such as spinosad, azadirachtin, and pyrethrins are approved for use in organic orchards.

To monitor for brown marmorated stink bug, use pheromone traps, inspect plants for the insect and its damage, and sample with beating trays.

Growing Degree-Days

The number of brown marmorated stink bug generations per year depends on seasonal temperatures. First-generation eggs are laid in midspring, but the specific timing is weather dependent. To calculate degree-days once the timing of egg laying has been identified, use a lower threshold of 62.6°F and an upper threshold of 91.4°F. For complete development (egg to adult), 538 degree-days (DD) are needed, plus 148 DD to egg laying, for a total of 686 DD from egg to egg.

Generations begin to overlap by July. The length of time in each stage also varies depending on seasonal temperatures. Generally, two full generations are expected. However, in cooler parts of California only one generation may occur and in the warmest areas of the state up to three generations may occur.

The degree-days model was developed in other states and has not been validated in California.

Traps, Lures, and Other Sampling Methods

A trap baited with a brown marmorated stink bug aggregation pheromone and pheromone synergist (methyl decatrienoate and murgantiol) is effective for monitoring adults and nymphs throughout the season, even when low numbers are present. Affix 9-by-12-inch double-sided sticky panel traps near the top of wooden stakes, about 4 feet above ground level. Suspend the lures at the top of the stakes near the sticky panels. For each orchard, use a minimum of three sticky panel traps, separated by approximately 160 feet to avoid interference. Place the traps in a tree row adjacent to open fields, houses, or other potential overwintering sites from which adult brown marmorated stink bug may migrate into the orchard. Traps effectively catch both adults and nymphs. It is important to carefully inspect traps for early nymphal stages (second and third instars) because this pest is small at these stages and hot summer weather can easily dry them out.

Trap captures may not represent brown marmorated stink bug density in a monitored orchard because lure performance can vary depending on the crop. As one of brown marmorated stink bug’s preferred hosts, peach often has trap counts that underrepresent an orchard’s population and damage, and adults and feeding activities have been seen in orchards where no trap captures were recorded.

If brown marmorated stink bug is believed to occur in the area, it is important to regularly scout for the pest’s life stages and damage in the orchard. Visually observing the insect (egg masses, nymphs, adults) and damaged (deformed) fruit, and sampling with a beating tray (shaking branches and twigs to dislodge insects onto a light-colored surface), are early detection methods. Conducting visual observations for the presence of insects and fruit damage in the trees along orchard edges is highly recommended. Sample in the early morning because adults may fly away during warmer times of the day. If eggs or young nymphs are found, an insecticide application targeting the more vulnerable nymphal stages may be warranted.

No treatment threshold has been developed for brown marmorated stink bug in peach orchards in California. At this time, the presence of any brown marmorated stink bugs in traps, together with a confirmation from visual surveys, should be of concern because peach is a preferred host of this pest. Consider a spring insecticide application for control; however, it is critical to properly identify this pest before making management decisions because many other insects can be mistaken for brown marmorated stink bug.

Because brown marmorated stink bug is a newly established pest in California, management programs for California crops are still being developed. Consult your local University of California Cooperative Extension advisor for more information on management plans for brown marmorated stink bug in your area.

Pyrethroid insecticides are considered effective against this pest. However, pyrethroids have short residual control. They are also a poor fit in an integrated pest management program, especially early in the season, because they kill natural enemies. For example, using pyrethroids in spring can cause an increase in spider mite numbers.

If multiple insecticide applications are needed, consider spraying follow-up applications along orchard edges because brown marmorated stink bug tends to be found along edges, near potential overwintering hosts.