Nov 8, 2010

Bug raising a stink this year

On Sept. 22, nearly 14,000 people visited the Penn State College of Agricultural Sciences’ website to learn about the brown marmorated stink bug.

The brown marmorated stink bug (BMSB) is relatively new to Pennsylvania and the United States. It is known to be a pest in its native range in Asia, but it was first noticed in Pennsylvania only in 1998. The bug has been a nuisance to homeowners for several years. It spends the winter as an adult in sheltered locations, so it begins to congregate on the outside of homes this time of year, and it can find its way inside, to the chagrin of residents.

This summer, however, we saw a different side of BMSB. It has emerged as a significant pest of food and feed crops. Fruit growers are noticing serious injury – the BMSB feeds by sucking plant fluids through its beak, and the damage at the feeding site leads to rejection of the fruit by the consuming public. In addition to fruit, BMSB is attacking a range of vegetables and even agronomic crops such as soybeans. Farmers may notice some significant loss of crop yield as harvest progresses.

BMSB are approximately 17 mm long, with shades of brown on both the upper and lower body surfaces. They are the typical “shield” shape of other stink bugs, almost as wide as they are long. To distinguish BMSB from other stink bugs, look for lighter bands on the antennae and darker bands on the membranous, overlapping part at the rear of the front pair of wings. They have patches of coppery or bluish-metallic-colored, 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.

Even though the bug has been around since 1998, it has caused a greater stir this year, according to Steven Jacobs, Extension entomologist in Penn State’s College of Agricultural Sciences.

“First, this year’s warm spring and early summer allowed the stink bug to reproduce at a faster pace,” Jacobs said. “Normally, you’d see one generation of stink bugs per growing season, but this year we’ve had three generations, leading to higher and faster-spreading populations.”

In fact, in parts of sub-tropical China, records indicate the pest may produce from four to possibly six generations per year. Adults will emerge sometime in the spring of the year (late April to mid-May) and mate and deposit eggs from May through August. The eggs hatch into small black and red nymphs that go through five molts. Adults begin to search for overwintering sites from September through the first half of October.

“But in addition to being a nuisance, it has become a serious agricultural pest, just as it is in its native range of China, Japan, Korea and Taiwan,” Jacobs said. “In 2010, stink bugs have caused extensive damage in some Pennsylvania apple and peach orchards and have been found feeding on blackberry, sweet corn, field corn and soybeans. In neighboring states, they also have damaged tomato, lima bean and green pepper crops. In all, they can attack an estimated 300 host-plant species.”

The real danger of the BMSB, is that it is such an important pest in apples that growers may feel compelled to apply additional pesticides to protect their crop. This could basically take us back 30 years in our efforts to work with orchardists to reduce pesticides based on the principles of integrated pest management, or IPM. We’ve helped apple growers drastically reduce their pesticide use over recent decades, all based on research that led to improved understanding of pest biology and the use of natural enemies and alternatives to chemical pesticides to manage the pests. These alternatives don’t control the BMSB, so a return to pesticide treatments targeting this new pest could completely disrupt our IPM progress.

Greg Krawczyk, tree fruit entomologist at Penn State’s Fruit Research and Extension Center in Biglerville, Pa., noted that because the insect is native to Asia, it has few if any natural enemies in the United States to help control its populations. And pesticides are not a particularly good option for growers, some of whom have lost 40 percent to 50 percent of their crops to stink bugs.

“If control is needed to protect fruit crops, our preliminary data suggest that broad-spectrum, contact insecticides should work best,” Krawczyk said. “But these compounds may not provide adequate control because they don’t show residual activity, meaning that bugs migrating into an orchard after spraying can start a new population very quickly.”

A Penn State fact sheet about BMSB is available at http://ento.psu.edu/extension/factsheets/brown-marmorated-stink-bug.

— By Bruce McPheron, Penn State University