A relatively new insect known to cause feeding damage in peaches and almonds is expanding its territory throughout the state, according to an entomologist with the University of California.

Mostly seen as a nuisance pest throughout the United States and in places like downtown Sacramento, the Brown marmorated stink bug (BMSB) can cause feeding damage on developing fruits and nuts, mostly from March to July, leading primarily to nut drop in almonds from March to May, says UC Integrated Pest Management Adviser Jhalendra Rijal.

Though the bugs can be found in great populations in urban and suburban areas, their existence is largely a nuisance in those cases since they are not harmful to humans or pets, though they can produce a malodorous chemical.

Particularly troublesome to agriculture, adults and all immature stages, except the first instar, can actively feed on developing fruit, leading to severe damage, Rijal says. Because they have a wide plant host range, control can be difficult.

The University of California reports that the BMSB is known to feed on over 100 different host plants in Asia, including tree fruit, vegetables, shade trees and leguminous crops. Elsewhere in the United States where the pest is well-established it is known to actively feed on stone fruit, lima beans, peppers, tomatoes, field corn, soybean, blueberries, grapes and pecans. Its wide host range coupled with an absence of natural enemies makes the pest one of concern throughout agricultural and within urban landscapes.

Identifying the insect can be tricky because other stink bug species look similar, Rijal says. Adult BMSB are about one-half to two-thirds of an inch long, and unlike other stink bug species, have white band marking on their antennae and legs.

Bugs can be collected for identification. Simply collect them in a sealed container, note where the insects were found, and deliver it to the local Cooperative Extension office for identification.

Typical population spikes happen from summer into fall. The pest will infest late season hosts before overwintering in a variety of locations, including under the peeling bark of older or dead trees, or in homes. Insecticides can help control the pest, though they are largely more effective on overwintering generations than summer generations.

First detected in Pennsylvania in the late 1990s, widespread economic loss spanning the Mid-Atlantic states was reported in 2010. The pest is now established in 16 California counties, including much of the northern half of the San Joaquin Valley. Several Sacramento Valley counties including Glenn, Butte, Sutter, Yolo and Sacramento also have established populations. Detections have been confirmed across southern California, except for Imperial County, where to date they have not been found.