Pecan growers in New Mexico and other areas of the Southwest have a new pest menace — the brown marmorated stink bug (BMSB) — that has the potential to take a serious bite out of profits.
Carol Sutherland, New Mexico State University Extension entomologist, says no one knows yet how it compares to native stink bugs in terms of a damage threat or how difficult it would be to control with available materials.
So far, the invasive pest hasn’t been found in any New Mexico pecan orchards in New Mexico, but last November it was discovered inside a trailer hauling household goods from southern Pennsylvania. Sutherland confirmed its identity.
Not long after that, it was found on a recreation vehicle in Corpus Christi, Texas, and more recently, a reproductive population of the insect was confirmed in that area.
A native of East Asia, it is believed to have entered the U.S. on cargo shipments, possibly from China, Japan or Korea. It was identified in Pennsylvania in 2001 and began causing widespread crop damage by 2009. It has since spread to at least 29 states.
Seven years ago, it was found in a cargo shipment at an airport in southern California, and it has appeared in tree fruit orchards in Oregon. Two years ago, apple and peach growers in the Northeast lost as much as 70 percent of their crops to BMSB.
“We don’t know yet,if the brown marmorated stink bug will be become a key pest of pecans,” Sutherland says. ”It took over a decade for the insect to be recognized as a key pest for a variety of crops, but it seems to be hitchhiking its way across country. The few findings of generally nondescript bugs in New Mexico and Texas make you wonder where else in this region they might be.”
Feeding by BMSB may cause immature nuts to fall, as well causing brown or black spots on harvested and cracked nut kernels. The mouth parts of stink bugs damage fruit in two ways — by puncturing the fruit, vegetable or nut, sucking up sap and nutrients, and also by injecting saliva into the feeding wound.
All stages of nymphs and adults may injure their plant hosts. But, the more likely cause of nut loss and kernel damage is the salivary enzymes the insects release as they feed, she notes.
“The enzymes in their saliva continues to act and kills the surrounding cells,” Sutherland says. “That causes sunken areas and brown or black spots on the nut or other affected fruit. It can also impart a bitter taste to the nut.”
Several species of stink bugs native to New Mexico and other areas of the Southwest can feed on pecan nuts. In 2010, for example, the conchuela (Chlorochroa ligata) was the likely culprit in many New Mexico pecan orchards, causing black and brown withered spots on pecan kernels.
The shield-shaped adult conchuela, about the size of a thumbnail, varies in color from dark green to very dark olive or even gray. Many have a narrow orange or reddish orange rim on their bodies.
Like other stink bug species, the conochuela and its nymphs blend in with their surroundings and will hide behind a branch or trunk of a tree when they detect any nearby movement.
“This pest is probably more common in orchards than many growers think,” Sutherland says. “They only find out how damaging this particular stink bug is after the crop is harvested and nuts are cracked and evaluated.
In New Mexico, pecans probably are most susceptible to feeding damage from stink bugs sometime after July 1, when the kernel is developing and before the woody shell develops around it.
“The kernel is just leaving the water stage and developing into the doughy stage,” Sutherland says. “There are lots of proteins, fats and complex carbohydrates to provide a very nice meal for the insect.”
The brown marmorated stink bug gets its name from the Latin word for marbled, marmor, to describe the marble-like pattern of tiny brown dots on the back of the adult. Another distinguishing feature, which none of the common western stink bugs have, are the white bands on its antennae.
While the host list for BMSB in east Asia is long, it is likely to get longer as the pest invades new areas in the U.S. and encounters new potential host plants, Sutherland says.
Its impact on the US pecan industry remains to be seen. It can also be a serious pest of apples, pears, cherries small fruits, grapes, and fruiting vegetables, including corn, tomatoes, peppers, and legumes. Also, it can severely damage ornamentals and nursery crops by feeding on buds, twigs, branches and the thin bark on young trunks.
In addition to its economic toll, BMSB is a major nuisance, especially in the fall when it gathers in large numbers around homes and other structures, and around outdoor lights.
“When overwintering, the bugs survive on stored body fat and won’t reproduce,” Sutherland says. “They find and enter any sort of crack or crevice in a structure or elsewhere in the environment. When that crevice leads to a void in a wall or attic, they can literally fill it up. Like other stink bugs, BMSB emits a strong, unpleasant odor when disturbed.”
In the U.S. the brown marmorated stink bug has few, if any, effective natural enemies. Adults are very strong flyers and can disperse into new habitats or reenter crop fields previously treated for other pests. She advises pecan growers to be on look out for the BMSB.
“You need to be on your toes for this creature,” Sutherland says. “If you see anything moving in your orchard, stop and take a closer look. Whack a branch with your hand or a tool and see if stink bugs fall off. Take anything you can’t identify to your county Extension agent to determine exactly what’s in your orchard.”
A variety of insecticides with different active ingredients and modes of action are currently registered in New Mexico, and probably most other states, for stink bugs, she says. “Many of these products have been registered on pecans for years.”
Scientists have launched major research efforts to determine the best methods to control BMSB. Although pyrethroids will kill on contact, this group of chemicals also kills beneficial insects. Researchers are also working on population monitoring methods, including a pheromone and trap combination that could be used to track populations over time.