The brown marmorated stink bug (Halyomorpha halys), simply known just as the stink bug is part of the Pentatomidae insect family that is native to China, Japan and Taiwan. It is considered to be an agricultural pest and has affected the crops of the United States since it was accidentally introduced in this country two decades ago. It can be easily identified by its shield-shaped body, which is almost as wide as it is long. With few natural predators in North America, BMSB has spread quickly in the United States, but also in other countries as well, where it also posses great threat to crops of all types. As it isn’t a picky eater, it can easily affect orchard crops, small fruit, grapes, vegetables, and ornamental plants throughout each growing season.
Description and distribution of stink bugs
The adult individual can reach 1.7 cm (0.67 in) long, as well as wide, forming the characteristic shield shape of the stink bug. They are colored in different shades of brown, with gray, off-white, black, copper, and bluish markings. They have patches of coppery or bluish-metallic colored punctures (small rounded depressions) on the head and pronotum. The name “stink bug” refers to the scent glands located on the dorsal surface of the abdomen and the underside of the thorax. Their eggs are elliptical, light yellow to yellow-red with minute spines forming fine lines. They are attached, side-by-side, to the underside of leaves in masses of 20 to 30 eggs.
The Brown Marmorated Stink Bug has five nymphal stages, and ranges in size from 2.4 mm to 17 mm in length. Unlike the adults who blend in very well with bark, the nymphs are more brightly colored with red and black. In the first stage, in which they have a “tick-like” appearance, the stink bugs are not very active and remain around the hatched egg mass. Nymphs are characterized by dark reddish eyes and a yellowish-red abdomen that is also striped with black, and wit legs and antennae colored in black with white banding.
This insect originated in China, Japan and Taiwan, but was introduces to other countries as well through packing crates shipped from its origin countries. As these bus are able to survive long periods of time in hot or cold conditions, it allowed them to enter the United States or other counties relatively easily, as the survived the means of transportation used. Currently stink bug populations are on the rise because the climate in the United States is ideal for their reproduction. In optimal conditions an adult stink bug will develop within 35 to 45 days after hatching. In warmer climates, multiple generations can occur annually, which can range from two generations in states such as Virginia to six generations in states such as California, Arizona, Florida, Louisiana, and Texas. Currently there does not appear to be any environmental limiting factors that are slowing their distribution across the United States. They also are extremely mobile insects capable of moving from host to host without causing disruption in their reproductive processes, as they are becoming an invasive species with a rapidly expanding range in North America and Europe.
Following the accidental introduction and initial discovery of stink bugs in Allentown, Pennsylvania, USA, this species has been detected in 41 states and the District of Columbia in the USA. Isolated populations also exist in Switzerland, France, Italy and Canada. Recent detections also have been reported in Germany and Liechtenstein. Ecological niche modelling indicates that the area of invasion suitable for the stink bug is quite extensive worldwide, so preventive measures must be thoroughly applied when it comes to this pest.
The stink bug as a pest – agricultural effects
This insect has over 100 reported host plants. It is widely considered to be an arboreal species and can frequently be found among woodlots. Such host plants are important for development as well as supporting populations, particularly during the initial spread into a region. Damage to apples and pears in the USA was first detected in Allentown, Pennsylvania, and Pittstown, New Jersey. In particular, peaches, nectarines, apples and Asian pears are heavily attacked. Feeding injury causes depressed or sunken areas that may become cat-faced as fruit develops, which renders the fruit as unmarketable, due to its lack of fresh appearance. Similar damage occurs in fruiting vegetables such as tomatoes and peppers, although frequently later in the season. Feeding can cause failure of seeds to develop in crops such as maize or soybean. The stink bug has also been found feeding on blackberry, sweet corn, field corn as well.
It is also known to cause allergic reactions (rhinitis and/or conjunctivitis) in some individuals who are sensitive to the bugs’ odor (an aeroallergen). These chemicals are produced by dorsal scent glands. Individuals sensitive to the odors of cockroaches and lady beetles are also affected by the BMSB. Additionally, if the insects are crushed or smashed against exposed skin they have been reported to produce dermatitis at the point of contact. This is particularly important regarding agricultural workers picking fruits and vegetables.
Controlling this pest has proved to be quite difficult due to the fact that they are developing resistance to certain insecticides. Also, as the bugs are mobile, and a new population may fly in after the resident population has been killed, making permanent removal nearly impossible. As new populations move back into the area, or the existing population simply moves to unaffected areas, the stink bug has proved to be a nuisance, especially to farmers.
Several spider species attacked both the eggs as well as live stink bugs. Woodlice eat stinkbug eggs. The wheel bug, however, is the most voracious predator and attacks the eggs as well as adult stink bugs more consistently. However, relaying on other insects as a means to deter stink bugs may not be the most efficient method. Mechanical exclusion is the best method to keep stink bugs from entering homes and buildings. Cracks around windows, doors, siding, utility pipes, behind chimneys, and underneath the wood fascia and other openings should be sealed with good quality silicone or silicone-latex caulk. Damaged screens on doors and windows should be repaired or replaced.
Exterior applications of insecticides may offer some minor relief from infestations where the task of completely sealing the exterior is difficult or impossible. Unfortunately, because insecticides are broken down by sunlight, the residual effect of the material will be greatly decreased and may not kill the insects much beyond several days or a week.
Nuisance impacts are especially problematic in rural areas, and have been reported in many urban and metropolitan regions. In the autumn, the stink bug moves to structures, often by the thousands, generating numerous complaints. Similar to the impacts on commercial growers, homeowners are also experiencing damage to backyard fruit and vegetable gardens. This is why preventive measures need to be applied early on, in the hopes that a stink bug infestation can be avoided.