The brown marmorated stink bug has managed to spread all across the world in the past two decades. [Credit: Peter Jentsch]
When Marianna Szucs moved to Michigan three years ago, she found hundreds of little black and brown insects, their hard shells knocking against each other, filling every crevice of her new house.
“It wasn’t that shocking because I’m an entomologist. I think it would shock other people more,” said Szucs, an insect biocontrol specialist who moved for her job at Michigan State University.
The intruders were brown marmorated stink bugs. They have infiltrated more than 33 countries and 46 U.S. states, and are spreading fast. In fact, experts say this Asian native is one of the most highly invasive species worldwide, and that its voracious appetite for almost anything green makes it a major threat to agriculture.
Not wishing to join the cohort of nations assailed by the insect, Australia and New Zealand are on high alert, says Valerie Caron, an entomologist at the University of Canberra in Australia. She says both countries are very worried about the stink bug’s potential for crop damage and have been taking stringent steps to try and prevent its arrival to their island nations.
With its low stance and brown, shield-shaped body (about two-thirds of an inch in each direction), the brown marmorated stink bug does not look like a fearsome pillager. Its success lies in its prowess as a ravenous eater and stubborn squatter, rather than as a powerful fighter.
Due to the vast range of plants stink bugs devour, it’s difficult to calculate the damage they inflict on crops. One horticulture group estimates that mid-Atlantic apple growers alone lost $37 million in 2010. A survey in 2012 reported that stink bugs nearly destroyed entire sweet corn crops and almost 40% of okra pods in Beltsville, Maryland.
The brown marmorated stink bug can probably eat more than 300 plant species, says Peter Jentsch, an entomologist at Cornell University. So “once they get in, it takes probably millions if not billions of dollars to just keep the lid on it.” The stink bug’s large palate also means that it is impossible to control via pesticide. If the stink bug can eat every crop, he adds, then you have to spray every crop — not a realistic solution.
What’s worse, even if entire fields were sprayed, the bugs can just move indoors. Pests are generally either urban or agricultural, rarely both, says Jentsch. But unfortunately, this bug has no problem trading trees for chairs and vice versa. Its presence in people’s homes is what makes management so difficult, he says — folks don’t want to fill their homes with insecticides.
As with most invasives, the brown marmorated has no predators outside of its native East Asia. One of its primary predators is the samurai wasp, which has also invaded the U.S., making it an “adventive” species. When it finds stink bug eggs, the tiny wasp lays its own eggs inside them. Then when the wasp larvae hatch, they consume the stink bug eggs that hosted them.
Jentsch says that while most entomologists would technically classify the samurai wasp as an invasive species, its net effect in North America has been positive because the wasp rarely targets any other insects. The problem is that there aren’t nearly enough samurai wasps to make a significant dent in the booming stink bug population.
Not wanting to even consider biocontrol and management strategies, New Zealand and Australia are being meticulous in preventing the stink bug from reaching their countries.
“We’re trying to be two steps ahead of the bug all the time,” says Caron, the Australian entomologist. Australia’s current policy is to intercept and inspect all arriving cargo at sea before it can reach port.
Being island nations, both Australia and New Zealand have a big advantage compared with other countries: they don’t need to worry about land borders and only need to be wary of stowaways on ships. But checking all cargo shipments is easier said than done. Both countries have extensive policies and protocols outlined on their respective websites that are specifically designed to keep the brown marmorated stink bug at bay.
Scrutinizing every cargo shipment is a huge undertaking, but crucial since the stink bug can latch onto essentially anything. Michigan State’s Szucs says that the big reason why the brown marmorated stink bug is such an effective invader is its hitchhiking ability. The bugs are incredibly robust and successful travelers: they cling to cars, trucks, and boats, and stay there for hours, finding new plants to feed on once they eventually hop off.
The bug’s tenacity and diverse diet mean that cargo searches have to be both precise and comprehensive. “This stink bug can come in any type of cargo, so they have to be really vigilant,” says Caron. Car orders from Italy have been especially problematic, she says; Australia has had to turn around several shipments of luxury vehicles.
But even Australia’s best efforts won’t be enough to keep the brown marmorated stink bug at bay forever. “Because it’s so widespread and it’s already in so many countries, we’re kind of bombarded,” says Caron.
There’s even a possibility that the bug may already be in Australia, but in populations too small to be easily detectable. “If it is introduced, it might take a couple of years before it’s found — it could be breeding now, and we don’t know,” says Caron. Regardless, she says, any years they can deny the brown marmorated stink bug access to Australian crops are worth the effort.
For the U.S., eradication is off the table, says Szucs — it’s simply too late. Even if a more aggressive attempt to control the brown marmorated with the samurai wasp was widely used, we are stuck with the stink bug for life, she says.
Szucs still gets stink bug lodgers every winter — they like to spend the colder seasons indoors. This year, there were probably fewer than 100, and she’s getting used to having them in her home life. “My cats eat them,” she says, “and their breath is really bad for a while, but it’s fine.”