Newark, Del. — The brown marmorated stink bugs that took a $37 million bite out of the Mid-Atlantic’s apple crop last year have awakened from winter hibernation, mated and morphed into a possibly larger threat to farmers and homeowners.
These stink bugs are the offspring of the same plague that freaked out Maryland, West Virginia and Pennsylvania homeowners last fall when they crawled into houses to hibernate after the feast, seeking warmth in cracks, and, in some cases, near sleeping humans.
They started creeping out of hibernation and coupling in late May. Their eggs hatched within three weeks, and their babies, or nymphs, reached adulthood within six weeks. They will possibly return to homes and other warm places when temperatures dip in late September.
Government entomologists say this year’s plague seems worse in many areas, and they expressed a particular worry about this invasive species from Asia, which has no natural predators in the United States. The warmth-loving insects appear to be migrating from eastern Pennsylvania, where they were first spotted in 1998, to the sunny Southeast, where the population might explode.
“If they get to Florida, it could be like the atomic bomb going off,” said Douglas G. Luster, research leader for the U.S. Department of Agriculture’s Agricultural Research Service. “They’re starting to show up in North Carolina.”
In a desperate search for a solution, the Environmental Protection Agency recently approved limited use of two insecticides to help control the pest, and researchers at a government lab in Delaware are conducting studies to determine whether a non-stinging parasitic wasp that preys on brown marmorated stink bug eggs in China, Japan and South Korea can be introduced here.
The Asian wasp isn’t much bigger than a period that ends a sentence, but introducing the insect is risky because it, too, could become invasive and attack native insects that are beneficial to the Mid-Atlantic’s ecosystem. If the wasp became a threat, it would join a host of species from Asia on the government’s most unwanted list of harmful plants, insects and animals.
But the risk might be worth it, entomologists said. Detected in 33 states and the District, the brown marmorated stink bug munches on hundreds of varieties of plants and trees. It has a taste for fructose, stabbing its mouth — or proboscis — into apples, peaches, grapes and other fruit at the start of harvest season. Last year, it ruined nearly half of Pennsylvania’s peach crop, worth $15 million, said experts at the Penn State Cooperative Extension.
“The growers who have the most fear are the fruit growers,” said Jerry Bruste, secretary and treasurer for the Maryland Vegetable Growers Association. “It will devastate them.”
In a secured section of the Beneficial Insect Introduction Research Unit at the University of Delaware in Newark, researcher Kathleen Tatman described last week how the Asian wasp kills the stink bug.
As stink bugs lounge on paulownia leaves and suck on vegetables and fruit, the wasps target stink bugs’ tiny clusters of perfectly round, milk-colored eggs and use them as hosts for larvae that eat them from the inside. Asian stink bug eggs are thought to be the perfect size for the wasp, its mortal enemy.
“There are many kinds of insects that are very specialized, feeding on only one or two other insects,” said Kim A. Hoelmer, a research entomologist who is leading the study. “Many times . . . an invasive insect or plant comes into North America . . . without its natural enemy. In Asia, [the stink bug] feeds on the same plants as here, but it never has a population explosion because of its predators.”
The United States has native parasitic wasps and native stink bugs, such as the spined soldier bug and the two-spotted stink bug , all beneficial species. But native wasps target a variety of insects, going after only 2 percent of brown marmorated stink bug eggs.
The fear is that the Asian wasp will diversify its attack and kill native species. Hoelmer said the wasp’s introduction won’t happen for at least another two years — or possibly not at all — as entomologists study how it behaves amid other species.
The last thing agriculturalists want is another bad-acting predator from Asia. They’re already in an uphill battle to control the Asian tiger mosquito, which slipped into Houston in a shipment of used tires in 1985.
Trade between the United States and Asia has increased nearly 80 percent over the past 10 years, causing more harmful species to slip into the country.
The Chinese mitten crab came via ships in 2005. Its constant burrowing erodes riverbanks. The Asian emerald ash borer arrived in 2002; it was stowed away in cargo ships. Its larvae feeds on native ash trees, killing them. And the northern snakehead was introduced from Asia in 2002 after a man released one into a Crofton pond; he had ordered it from a New York market for medicinal purposes. Snakeheads eat native fish in the Chesapeake Bay watershed.
No matter whether they’re less than an inch, such as the Mexican fruit fly, or up to 28 feet, such as the Asian reticulated python, invasive species can wreak havoc on native plants and animals.
The larvae of fruit flies gorge themselves each year on millions of dollars worth of Texas citrus. Florida formed a Python Patrol to deal with an estimated 30,000 snakes in the Everglades that eat everything from mice to deer to alligators but fear no natural predator. The United States hosts hundreds of invasive species in every state.
Regardless of the risk, “the wasps are needed” to control the brown marmorated stink bug and its damage to crops, said Tracy Leskey, a research entomologist for the Agricultural Research Service.
“This is our priority number one for sure,” Leskey said. Research was stepped up because of the brown marmorated stink bug’s population boom. “In an experiment, we trapped 15 gallons of stink bugs in three months last year: August, September and October.”
Vegetable growers in some areas have spotted the insect’s bites on every kernel on an ear of corn. Winery owners in the Mid-Atlantic and on the Pacific Coast said the insect’s odor changed the flavor of wine when a few were mixed with crushed grapes.
The EPA has approved two insecticides, including dinotefuran, sold under the names Venom and Scorpion, for emergency use. The poison is effective, farmers said, but has a major downside.
“You kill some” with the insecticide, but it kills the natural enemies of other pests that prey on crops, Bruste said. Having wiped them out, “you’re totally dependent on chemicals,” which are expensive.
Dan Derr, owner and operator of Spring Valley Farm in Cecil County, Md., said stink bugs ruined at least a third of his peach crop this year. On a scale of one to 10, Derr said, his level of worry is at an eight. He welcomed government efforts to end the threat.
“It’s just that, all of a sudden, they start swarming,” he said. Derr said he could afford to lose half of his peaches but not his chief crop. “I don’t want them to get in my blueberries.”