By Bryan Jensen
The brown marmorated stink bug (BMSB) is a new stink bug species which was first detected in North America in 2001 and Wisconsin during 2010. BMSB has a wide host range and overwinter as adults. Likely, there will be a single generation per year in our state. Nymphs were recently observed by PJ Liesch, UW Insect Diagnostic Lab, and I thought it would be a good time to give you a quick heads-up.
After initial detection within an area/state, the normal progression of events is that BMSB first becomes established as a household nuisance before they become an economic agricultural pest. In some areas of the state we are past that first stage and now is the time to start looking for them in the field. Likely, we are a few years away from significant problems, however, it is better to become familiar with them prior to a serious infestation.
We do have several native stink bug species that can be found in agricultural setting but there are subtle differences. Most native adult stink bugs are slightly smaller (1/2 inch) compared to BMSB (5/8 inch). All species, including BMSB, will have a very distinct “shield-shape”. The most identifiable characteristics of the adult BMSB are 1) alternating light to brown spots on the outer edge of their abdomen 2) antennae have alternating brown and light bands and 3) the eyes of fresh specimens are dark red. Please see PJ’s ID picture below. BMSB do have brown/white mottling; however, this characteristic does not separate BMSB from native stink bugs. The immature BMSB is smaller than the adults and range in size from a pin head to ½ inch in length. Nymphs are oval and have dark red eyes similar to adults. Nymphs vary in color and appearance with age. Initially, they range in color from a yellowish red to a creamy white with reddish spots just prior to turning into adults.
BMSB have piercing sucking mouth parts and damage to corn and soybean is commonly found along field edges. In soybean, economic damage is from pod and/or seed feeding which results in absent, discolored or shriveled seed. Furthermore, foliage may stay green longer. In corn BMSB feed through the husk and individual kernels may become shriveled and discolored.
Economic thresholds specific to BMSB have not been established. Until more information is known, consider treating soybean if 40 stink bugs are found/100 sweeps. In corn, economic thresholds are not well developed especially for the reproductive stages. Again, economic damage is not expected at this point in time.