The real dirt: Watch for with the invasion of the brown marmorated stink bug

The brown marmorated stink bug is a plant-destroying pest making its way into the area now.The brown marmorated stink bug is a plant-destroying pest making its way into the area now.U.S. Department of AgricultureBe on the lookout for the brown marmorated stink bug, says Emily Symmes, the newly-appointed Butte County Director for UC Cooperative Extension.

Symmes, who earned her Ph.D. in entomology at UC Davis, also covers five Northern California counties as integrated pest management adviser.

In a recent talk given to the Butte County Master Gardeners on the topic of emerging arthropod pests, Symmes provided a great deal of useful information on the stink bug (halyomorpha halys) and stressed the importance of educating community members so they can recognize and prevent the spread of this voracious pest.

There are a large number of stink bugs — all “true bugs” in the order Hemiptera — whose common trait is the piercing-sucking mouth part (stylus) which can do great damage to commercial and ornamental plants.

The brown marmorated stink bug is an equal-opportunity feeder, foraging on up to 300 species of produce, trees, and other vegetation, according to some estimates. Although serious commercial crop damage has been limited to the Eastern U.S., the bug is on the move in California, and could pose a threat to Northern California farmers and ranchers. It may include almonds in its culinary repertoire although problems have not been observed yet.

This pest doesn’t limit itself to the outdoors. Because it likes warm conditions, in late summer and early fall it will seek shelter in the warm cavities between residential home walls, and even in cars. The first brown marmorated stink bug formally identified in Butte County was found crawling on the walls of the enclosed back porch of this writer’s home in July of 2013. A few months later, I spotted one inside my car.

Resist the urge to smash it: the stink bug earned its colloquial name for a very good reason.

Stowed away on a cargo ship from Asia, the brown marmorated stink bug entered the U.S. in the late ’90s. According to a 2012 article in the Wall Street Journal, the U.S. Department of Agriculture noted that this immigrant pest had spread to 36 states; in 2010 trade groups reported $37 million worth of damage to apple crops alone.

In California a reproducing population was first found in the Los Angeles County areas of Pasadena and San Marino in 2006. The bug has since been detected in many other parts of the state, making its way north to Sacramento and Yuba City by 2013.

During her presentation, Symmes pointed out that home gardeners can be of key assistance in preventing the spread of this exotic, invasive species.


The brown marmorated stink bug exhibits the traditional shield-shaped body of all stink bugs and is five-eighths of an inch long. Distinct white and brown bands on its antennae and legs distinguish it from other stink bugs.

“Marmorated” means streaked or marbled, and the body of this particular stink bug is mottled in shades of brown. It lays barrel-shaped eggs in tidy rows on the underside of leaves; these eggs range in color from white to pale green.

While the number of its life cycles in our area is not known, the bugs are inactive during the colder months, and produce more generations in warmer climates. Please see for identifying specifics about the bug’s five nymphal instar stages before adulthood.


Brown marmorated stink bug nymphs and adults feed on leaf and fruit tissue by injecting digestive enzymes to facilitate nutrient extraction. This feeding results in localized necrotic spots. Direct feeding on developing fruit can lead to severe distortion and in some cases fruit drop.

Stink bugs can also contaminate fruit products. For example, if infested grapevine clusters are pressed for their juice, the bugs will also be crushed, and the juice destroyed.

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