BATTLE OF THE BUGS
Josh Milnes, a graduate student at Washington State University, is using tiny wasps to fight off an invasive stink bug species threatening Washington’s crops.
Story by Madeleine Jeffers | Photos by North Joffe-Nelson
Two dozen baby-blue eggs, collectively the size of a grain of rice, lie on a small, green leaf. Although they were laid by a brown marmorated stink bug, an entirely different insect emerges. At first, they appear to be miniature black ants, but closer inspection reveals them to be tiny wasps. Observing this process through a microscope, Josh Milnes, an entomology graduate student at Washington State University, is on a mission to protect Washington state’s agricultural industry with the samurai wasp.
A new invasive species from East Asia, called the brown marmorated stink bug, is threatening agriculture in Washington state. First discovered in Allentown, Pennsylvania in the late-1990s, the stink bug has made its way across North America. Although it targets a wide-range of crops, from vegetables to legumes, the stink bug is primarily drawn to tree fruits, including apples, pears, cherries, and peaches. Brown, hexagonal in body shape and the size of a thumbnail, the bug inflicts damage by piercing the surface of its dinner with it’s long nose. Apples attacked by the stink bug look diseased, covered in small brown bruises reaching all the way to the core.
In 2010, the brown marmorated stink bug population skyrocketed, causing $37 million in damages to apple growers in the Mid-Atlantic. During the same time, the bug also made its way to the Northwest, crossing the Oregon border into Clark County. Since then, it has been spotted in 21 of Washington’s 39 counties.
As the stink bug travels across the state, many people are concerned for Washington’s apples, an industry worth $2.4 billion a year. But Milnes is preparing a counter-attack. His research, taking place in Prosser, Washington, focuses on the samurai wasp — the stink bug’s natural predator — as a first line of offense.
Smaller than a sesame seed, the wasp is a reminder that looks can be deceiving. The wasp is a parasitoid, meaning it lays its eggs inside stink bug eggs. Similar to the film Alien, the developing wasps kill the hosts before they can surface as full-grown adults.
Milnes was first introduced to the stink bug in 2015. He set out to find other organisms that might counter the bug and soon discovered the samurai wasp. Like Batman and the Joker, the samurai wasp and the brown marmorated stink bug are natural enemies.
“This wasp is our long-term solution, we believe, to regulating the stink bug populations,” Milnes said.
Although others across the country are conducting similar research — including the United States Department of Agriculture — Milnes is in a unique situation. Because he found the samurai wasp already living in Vancouver, Washington, he can release the wasp throughout the state without government permission. In fact, the samurai wasp has made appearances in nine other states.
“The cat is out of the bag already,” said entomologist Merrill Peterson at Western Washington University. Whether they are released by scientists or get there on their own, the wasps will eventually end up spreading, he said.
Although the agricultural industry is in danger, urban areas currently contain the most stink bugs because they travel with people. So, homeowners should also be on the lookout.
“I probably had maybe twelve on my windows upstairs in my bedroom and they have been coming into the house as well. One grazed me coming out of the shower,” said Melinda Presley, an Olympia resident. “I have been known to eat stink bugs by mistake, so I make sure I look at my blackberries before I pop them in my mouth.”
The bugs tend to hide as the weather gets colder, so their presence does not bother Presley for now. But some Washington residents may not be as comfortable sharing their home. Stink bugs are appropriately named for the distinct odor they emit when crushed, which Milnes compared to cilantro or a smelly sock.
Even though homes and agriculture are being invaded, not everyone is on board with the use of samurai wasps as a response.
“I tend to be pretty uncomfortable with the notion of nonnative species being used to control other nonnative species,” said Patrick Tobin, an insect ecologist at the University of Washington.
But extensive research on the subject leaves Tobin on the fence. Scientists know the wasp will also go after native stink bugs, but they don’t know what the environmental impacts of that will be. The challenge is weighing known economic impacts with unknown environmental ones, he said.
However, Milnes is confident the samurai wasp will not have severe long-term effects on native stink bugs, nor the ecological health of the state.
The samurai wasp strongly prefers to parasitize brown marmorated stink bug eggs, Milnes said. These eggs are the ideal habitat for their development. The question is, what happens if there are no brown marmorated stink bug eggs nearby? The samurai wasp will use native stink bug eggs. However, those circumstances are not ideal and the wasps will be significantly less successful in producing offspring. Native eggs tend to be smaller, with thicker shells. This makes them tougher to break through, so many wasps die trying to emerge. Because of this, Milnes claims the populations of the brown marmorated stink bug and the samurai wasp will eventually reach a balance.
Chris Looney, an entomologist at the Washington State Department of Agriculture, believes biological control is the preferred instrument for controlling invasive species, compared to the widespread use of pesticides.
“We know from the experience back East that [the stink . bug] has the potential to be a serious agricultural pest, and honestly, it is probably just a matter of time until it starts having that role in Washington state,” Looney said.
Just like spotting a disease before the symptoms set in, scientists and farmers hope Washington can halt the spread of the brown marmorated stink bug before it causes significant agricultural and economic damage.
“If we do this right, we can hopefully stop the stink bug population from moving into the [agricultural] industry. That’s one of my goals, I would love to see that,” Milnes said. “We’re fighting a war and Washington state is at the frontline.”
