The Brown Marmorated Stink Bug (BMSB) is a shield-shaped insect known for the noxious chemical odor it releases when threatened or crushed. They are a common household nuisance because they congregate in large numbers to seek shelter, often entering homes and other structures to overwinter. Fluctuations in their visibility and population size result from their establishment in a new environment, their life cycle, and the development of natural and human-driven controls.
The Invasion and Establishment
The Brown Marmorated Stink Bug was first documented in North America around 1998, having accidentally arrived as a stowaway, likely in shipping containers from East Asia. This introduction marked the beginning of a rapid geographical spread throughout the United States and Canada. The insect thrived and multiplied quickly because it arrived without its natural predators and parasites, creating a “lag period” where its population exploded unchecked. Its wide-ranging diet, which includes over 100 plant species, contributed to its successful establishment across diverse climates and habitats, leading to the massive populations observed in the 2010s.
Seasonal Movement and Visibility
The public’s perception of the stink bug population is heavily influenced by its annual behavioral cycle. As temperatures drop in the fall, adult bugs enter a resting state called facultative diapause, seeking protected locations for overwintering. This is when they become a noticeable household nuisance, aggregating on the sunny sides of buildings and entering homes through small cracks. Once inside, they remain dormant until the following spring, often hiding in attics, wall voids, or behind baseboards. When warmer weather returns, the overwintering adults emerge from their resting sites and move back outside to feed, mate, and lay eggs, which explains why they suddenly reappear indoors and then vanish from the home.
Biological and Environmental Population Controls
The population of the BMSB has begun to ease due to the emergence of both biological and environmental controls. The most significant biological factor is the parasitic Samurai Wasp, Trissolcus japonicus, a specialized natural enemy from the BMSB’s native range in Asia. This tiny wasp attacks the stink bug by laying its own eggs inside the BMSB eggs, preventing the stink bug from developing. Although the Samurai Wasp was being studied in quarantine for potential release, adventive populations were discovered in the United States in 2014. Its establishment is now contributing to a long-term reduction in stink bug numbers by successfully parasitizing a high percentage of egg masses.
Environmental factors also regulate the BMSB population across North America. Severe cold snaps during the winter months can cause high mortality rates among the overwintering adults, especially those that chose less-protected shelters. Furthermore, prolonged periods of cool, wet weather in the spring can negatively affect the viability of the eggs and the survival of the newly hatched nymphs. These weather-related pressures, combined with predation from native generalist predators like spiders and earwigs, prevent the population from reaching the peak numbers seen during the initial invasion.
Human-Implemented Management Strategies
Human intervention continues to manage the BMSB, particularly in agricultural settings and residential areas. Integrated Pest Management (IPM) techniques are used to mitigate crop damage, including the deployment of specialized pheromone-baited traps to monitor and mass-trap the bugs. Researchers use synthetic aggregation pheromones that are effective at attracting the insects, allowing growers to target pesticide applications more effectively or to use perimeter-based treatments on the edges of fields. For homeowners, the most effective strategy is exclusion, which involves sealing exterior cracks and crevices, repairing damaged window screens, and ensuring doors are properly weather-stripped before the adults seek overwintering sites in the fall. Chemical controls, such as broad-spectrum insecticides, are generally restricted to agricultural use and are not recommended for indoor nuisance control.