Have you noticed more stink bugs in your home in recent years? It’s not your imagination. The brown marmorated stink bug, halyomorpha halys, an invasive species native to Asia, has exploded since making its way to New York State in 2007, causing millions of dollars in crop damage and making a nuisance of themselves to homeowners.
Their odor, which they emit when stressed, has been likened to a smelly sock or pungent cilantro. But the problem isn’t how they smell; it’s what they eat, which is pretty much everything.
Unlike our native stink bugs, this species has no natural predators. They’re hard to kill for a few reasons. At around 1.7 cm, they’re quite large for an agricultural pest, which means more pesticide is needed to be lethal. The bugs tend to do a lot of damage at the end of the season, when pesticide application needs to be tapered off to minimize the hazard for consumers. Beyond size, they have other physical characteristics that make them less vulnerable. Only the tips of their legs make contact with fruit or leaves when they walk, which minimizes the surface area where they can absorb the pesticide. They feed by penetrating their proboscis into the fruit or vegetable, which also minimizes their contact with the surface. They’re also mobile, able to fly miles from one farm to another, so even if a local population is reduced significantly, a new group can quickly take its place.
Not content to suck the life out of our apples, beans and peppers, they also invade our homes each fall to wait out the cold weather. A drowsy stink bug bouncing off a light fixture in the dead of winter is now a common sight. Some homeowners find themselves hosting thousands. When stink bugs find a good spot to hide, they secrete an aggregation pheromone that attracts other individuals. A Maryland wildlife biologist counted 26,000 in his home in one six-month period.
As Kathryn Schulz put it in The New Yorker, “the brown marmorated stink bug has made a name for itself by simultaneously threatening millions of acres of American farmland and grossing out the occupants of millions of American homes.” It is this dual role that has inspired scientists to seek help from the public in controlling its numbers.
A new citizen-science program by the Hudson Valley Research Laboratory in Highland is seeking local volunteers to help release the stink bug’s natural predator, the samurai wasp, trissolcus japonicus, which seeks out stink bug eggs and lays its own eggs in them. It’s estimated that 60 to 90 percent of brown marmorated stink bug eggs in Asia are destroyed in this way. While the stink bugs are rather large and dietarily indiscriminate, their foe is small (just 2 millimeters) and specialized.
In 2017, the wasps were introduced on 28 orchards in six New York State counties. Scientists want to expand the program beyond the fields and orchards to target other areas where the stink bugs over-winter.
“The general public participation is absolutely critical,” said Peter J. Jentsch, senior extension associate at the lab. If the samurai wasp can be established near homes where the stink bug over-winters, it can immediately reduce the population in the early season before a second generation is hatched, which is when it really does the most agricultural damage. “The people that are really growing large volumes of food are just struggling with trying to control this insect and [the public’s] participation really does make a difference in being able to reduce the brown marmorated stink bug population before they really can escalate late in the season,” said Jentsch.
The obvious question is whether the introduction of the wasps might have unintended consequences. As sciencemag.org notes, “many of the best-known biocontrol efforts are the historical disasters: the mongooses unleashed for rat control in Hawaii in 1883 that devastated native birds and turtles, and the cane toads sent to Australia in 1935 that failed to control sugarcane-destroying beetles but—because the toads themselves are poisonous—killed native reptiles, frogs, birds, and mammals that ate the toads.” Less well-known are the successes. Apoanagyrus lopezi, another parasitic wasp, has been used in Africa and Southeast Asia to control the cassava mealybug, saving millions of lives without harming other species in the ecosystem. In the first half of the 20th century, the introduction of two beetles from Australia helped halt the spread of klamanth weed (aka St. John’s Wart), which induces light sensitivity and causes skin problems when ingested by livestock.
Jentsch acknowledged that the wasps could have some impact on native stink bug populations. He mentioned the spined soldier bug, a beneficial predatory stink bug that feeds on variety of other arthropods, as one of the few stink bugs whose eggs the wasp also will prey on in the absence of its preferred host. But taking into account the relatively small expected harm, and weighing it against the damage wrought by the brown marmorated stink bug and the large volume of pesticide needed to keep it at bay, he says the consensus is that the samurai wasp is the best solution.
Locally, prior to any local distribution of the wasp by scientists, a population of wasps was found in Milton on Hepworth Farms, an organic vegetable grower, in 2016. So the program is not so much an introduction of a non-native species as it is a boost to one who found its way here anyway, helping the wasp population grow faster than it would on its own to bring the stink bug to heel sooner.
Participants will receive a Petri dish with “parasitized” stink bug eggs— that is, eggs laid by lab-raised stink bugs that lab-raised wasps have laid their own eggs inside. They will then hang the dishes on a tree near their homes and, after a few weeks, collect the dishes and return them to the lab via mail for analysis (researchers want to see how many hatched).
Those interested in participating should send an e-mail to ek538@cornell.edu using the subject heading “Samurai Wasp Redistribution.” A donation is requested to offset the cost of shipping and handling, as well as other program costs. Shipments will begin in early June.
Jentsch said there are no plans to repeat the program next year and, though samurai wasps have been released by scientists elsewhere, he isn’t aware of any other programs open to the general public. If you’d like to be involved, this could be your one and only shot.
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