The brown marmorated stink bug (BMSB), native to eastern Asia, is an invasive pest insect which was introduced to North America in the mid-1990s, and subsequently spread into many other countries in the following years. In the USA, BSMB have been detected in 42 states. They are most problematic in the mid-Atlantic states; a large outbreak of BSMB in 2010 caused an estimated $37 million in damages to this region’s apple crop alone. Brown marmorated stink bugs are polyphagous, feeding on a list of more than 170 host plants. They cause serious damage to many row crops, tree crops, ornamentals, specialty crops, and wild plant species.  Although they are polyphagous, some host plants provide poor nutrition for them, so normal development requires a diverse diet with multiple host plant species.

BSMB development requires a host plant with fruiting structures, and the bugs preferentially feed on fruits, moving from host species to host species to find what is in season. The nymphs seem to prefer fruit which has not yet been fed upon, perhaps because the nutritional content is higher. Both adults and nymphs readily relocate to find a more suitable plant host, contributing to their ability to invade new areas quickly. Their movement seems to be guided by volatile compounds released by plants and developing fruit. Adult brown marmorated stink bugs are capable of long-distance flight, with some individuals flying up to 100 km in 24 hours. However, this is an extreme case. Most individuals fly an average of 5-6 km per month, and walk the rest of the time. In field conditions, nymphs can walk up to 20 meters in 4 hours, meaning they can quickly travel between wild habitats and connected agricultural landscapes. Forest habitats play a role in stink bug development, and stink bugs spend time in both forests and open agricultural fields. Stink bugs are considered primarily nocturnal and more active at night.

Photo of an adult brown marmorated stink bug. Image from Flickr.

Hailing from Asia, BSMB are intolerant of cold temperatures, but they are able to acclimate to colder regional climates. Adult brown marmorated stink bugs overwinter in sheltered locations such as beneath dead bark, in rocky outcroppings, or in man-made structures. In the mid-Atlantic states, the adult BSMB begin to emerge from their overwintering sites in April. The emerging adults locate food and use their mouthparts to pierce and suck nutrition from the leaves of trees in forested areas, or young agricultural crops in the critical early growth stage.

Female BSMB begin to deposit eggs on the undersides of leaves after about two weeks of feeding, and feeding and egg laying continues throughout the summer. Females can deposit about 30 eggs at a time and up to 15 egg masses in a lifetime. The eggs take 35-45 days to hatch, depending on the incubation temperature. Stink bugs can have upwards of two generations per year in the right climate, allowing their population to rapidly expand. Additionally, overwintered females seem to produce more eggs than first-time egg-layers.

There are a number of stink bug species native to North America. Within the southeastern USA, there are three native stink bug species that cause the most problems in agriculture. These species are Euschistus servus, Euschistus tristigmus, and Chinavia hilaris. A large-scale study conducted in 2021 found that E. servus was more often found associated with crops, whereas the other two species were more often associated with forest habitats. Both Euschistus species are pests of corn, cotton, elderberry, and peanuts in the region. C. hilaris feeds on cotton, as corn and peanuts are a poor host for this species. C. hilaris also feeds on black cherry, elderberry, and mimosa. All three of these stink bug species as well as the brown marmorated stink bug seem to preferentially colonize host plants near forest edges. A 2014 study found that stink bug densities were consistently higher in fields adjacent to forest habitat compared to fields in open areas, indicating that forest habitats play a significant role in the development of these bugs.

Photo of a brown marmorated stink bug nymph. Image from Flickr.

The piercing mouthparts of stink bugs leave small discolored pinpricks or bruises on fruit. In corn and beans, feeding sites can shrivel and discolor. In tomatoes and peppers, the feeding site is often lighter colored than the rest of the fruit, and severe feeding may discolor the entire fruit. Fruits that have been fed upon may develop a corky texture below the skin of the injured areas. In addition to the direct damage caused by their feeding, stink bugs may increase the prevalence of certain pathogens by transmitting them while feeding on plants. Stink bugs have specifically been tied to the transmission of anthracnose on tomato plants caused by Colletotrichum.

A wide range of generalist predators such as beetles, spiders, slugs, and even small vertebrates prey upon BSMB adults, nymphs, and eggs. Supporting populations of these natural predators is foundational in the control of stink bugs and other pest insects. A two-year field study on multiple crop species found that total predation of BSMB eggs only reached around 10%. These results are consistent with other studies, indicating that biological control of BSMB is somewhat ineffective. The authors found that the rates of predation tended to be significantly higher in organically grown crops as compared to conventionally grown crops, indicating that organic systems support more natural enemies of stink bugs.

Within the USA, there are at least 12 native parasitoid wasps which are able to parasitize the eggs of BSMB. There are many more parasitoids from the stink bug’s native range in Asia, some of which have been intentionally or accidentally imported to be researched as biocontrol agents. That said, research has found very low rates of parasitism (<5%) by parasitoid wasps, indicating that other types of predation are more important than parasitism in the context of stink bug biocontrol. However, most of these studies on parasitoid wasps have involved “sentinel” egg masses placed by the researchers, rather than naturally-laid egg masses. Researchers suggest that this could be suppressing parasitism rates in their studies by removing some of the chemical cues that parasitoid wasps use to find the eggs.

Typical organic pest remedies, such as neem oil and insecticidal soap, are relatively ineffective against adult BSMB, but can cause >60% mortality in nymphs. A particle film of kaolin sprayed on plants was shown to be effective protection against adults and nymphs. Spinosad and pyrethrins (organic insecticides) have shown promise in laboratory studies but have yet to be proven effective in field settings. Organic insecticides are often detrimental to the populations of predators and pollinators as well, and using these products can actually lead to more outbreaks in the future by eliminating their predators. Stink bugs are mobile, and field applications of any insecticidal spray will only affect bugs which happen to be on those plants at that specific time, likely leaving lots of nearby stink bugs unaffected.

Methyl (2E,4E,6Z)-decatrienoate (known as MDT) and the BSMB pheromone have been used in the field to cause BMSB aggregation in an attract-and-kill system. In combination, MDT and BSMB pheromones applied to apple trees retained adult BSMB for nearly 24 hours, compared to only 3 hours on unbaited trees. There is potential for these pheromones to be used to aggregate stink bugs in one location for a more effective insecticidal treatment. In addition, a 2014 study discovered that the density of stink bugs was highest within 3 meters of the edge of farm plots, and reached the lowest densities more than 9 meters from the edge. With this insight in mind, any insecticidal treatments aimed at stink bugs could be applied around the edges of a field rather than the entire field, with large reductions in treatment cost while retaining high efficacy.

Trap cropping with a polyculture of flowering plants such as sunflower and sorghum can attract stink bugs away from the main cash crop. A 2017 study examined the effects of a sunflower and sorghum trap crop around the perimeter of a cash crop of peppers. The authors found that the trap crop harbored greater densities of stink bugs than the peppers, but unfortunately this only reduced pepper injury by 2%. However, a perimeter of attractive plants may have actually attracted more stink bugs towards the peppers, counteracting the intended effect. Perhaps side-by-side plots of trap crops and cash crops would be more effective and attract more bugs away from the cash crop. Trap cropping to control stink bugs is a relatively new system that is still being developed and improved.

Preventing stink bug damage by placing barrier screens over plants has been tested before and is effective, although labor-intensive. A 2016 study conducted on peppers found that mesh screens with an opening size of 1/6- to 1/8 inch were enough to reduce stink bug damage in areas with minimal stink bug populations. In areas with large populations and high stink bug pressure, mesh screens with an opening size of 1/25 inch were more effective, but also excluded some beneficial species, creating opportunities for outbreaks of secondary pests like aphids.