Answer for controlling stink bug population may rest with other pests

Penn State researchers think they might be able to solve, or at least control, the invasion of stink bugs — those shield-shaped invaders from the Far East that seemingly have become permanent residents in Southwestern Pennsylvania.

An ally in nature could be the answer in helping keep in check the unwelcome insects, which are a nuisance to homeowners when they head indoors for the winter and a costly pest to growers of tree fruits and soft-skinned vegetables that provide warm-weather sustenance for the next generation of the bugs.

State officials estimate brown marmorated stink bugs, which emit a foul smell when disturbed, last year cost growers $35 million worth of apples that could not be sold after the insects scarred them while dining.

In response, Penn State researchers hope to identify other insects that can perform pest control by laying their eggs in and eventually destroying stink bug eggs.

Hillary Peterson, a doctoral student from Brunswick, Maine, last year discovered that the tiny samurai wasp, another foreign invader in Southeastern Pennsylvania, does just that. While researchers study whether it will be effective and safe to culture and release the samurai wasp as a biological control, Peterson is testing how well wasps native to Pennsylvania can perform the same task.

“I hope that native (wasps) will adapt to utilize brown marmorated stink bug eggs, but it could take decades,” Peterson said when announcing the project. “Sometimes, (the wasp eggs') development is not successful because they have not evolved with these bugs.”

Scientists haven't traced exactly how stink bugs made the journey from their native habitats in China, Japan, the Koreas and Taiwan to the Allentown area in eastern Pennsylvania, where they were discovered in 1998. Since then, the pest has spread throughout the state and much of the country.

It's too early to tell how large the stink bug population will be in the region this growing season, said Lee Stivers, a Penn State extension educator based in Washington County who specializes in horticulture. Now that the bugs have been in the area for a number of years, growers “know they're here and that they need to manage them along with other insect pests,” she said.

According to Stivers, pesticides — if timed right — can be effective in controlling stink bugs. Fabric row covers also can provide an alternative for smaller, organic farmers.

Stink bugs are most susceptible in their small, nymph stage, before they fully mature, Stivers said.

“Like most insect pests, the earlier you come in with a control measure, the greater chance of effective control you'll have — when the population is still small, or the individual insects are in an early stage,” she said.

Jeff Norman annually uses a pesticide to protect his 20-acre apple orchard near Tarentum from stink bugs.

“We have to spray insecticide to control them in the spring and summer,” he said. “They sting the fruit and cause deformities.”

Instead of selling them in their most valuable, whole state, he may convert the damaged fruit into apple butter or cider.

Three years ago, when the bugs were at their peak, they damaged about 10 percent of his crop, Norman said.

Fortunately, the bugs' numbers seem to have dropped off, at least to Stivers.

“The frequency of me seeing them in the orchard is probably down about 40 percent,” he said.

Over the past several years, stink bugs have sucked some of the juice out of Unity farmer Neil Palmer's tomato crops — but not enough to warrant treatment with a pesticide.

“I'm on guard for stink bug damage, but I've just been grateful that it hasn't been too bad,” Palmer said. “We scout our plants regularly for pest damage twice a week throughout the season. One out of every few hundred tomatoes may be damaged.”

Former Irwin-area resident Michael Skvarla, director of Penn State's insect identification lab, noted stink bugs may be displaying the downswing that a non-native species can experience after initially surging into new territory.

“Oftentimes, the population will lower and just kind of stabilize at whatever the local environment can sustain,” he said. “Now, they're probably past the hump stage. Unfortunately, they're here to stay.”

Jeff Himler is a Tribune-Review staff writer. Reach him at 724-836-6622, jhimler@tribweb.com or via Twitter @jhimler_news.