Scientists want to use the Samurai Wasp to fight Michigan's invasive stink bug problem

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After years of waging a losing war against an invasive stink bug, scientists believe they may have found a solution. 

It’s hairy, has two zany antennas, eyes half the size of its head and legs colored iridescent orange - it also flies. A natural predator of the invasive brown marmorated stink bug, its introduction represents a new stage in the fight against invasive species. 

Since arriving in the U.S, the invasive stink bug has proven a nuisance to homeowners in the winter and a complete nightmare to farmers in the summer. Resistant to pesticides and without a native predator, the insect has wreaked havoc across the country. However, researchers have shifted efforts toward biological control. They’re now using a fight fire-with-fire technique; a parasitic wasp that burrows inside the invasive stink bug’s eggs. 

And so far, early results are promising.

Harmless to the touch but no less icky to look at, this particular stink bug is native to Japan. It made landfall in the U.S. in the mid-1990’s, first arriving in Pennsylvania, most likely stowed in packing crates from China or Japan. From there, it spread to 44 states, including Michigan. 

"It arrived in Michigan in 2010, and by 2018 it had caused serious economic damage," said Marianna Szucs, an assistant professor at Michigan State. "It usually takes about 10 years to start seeing damage, and that’s where Michigan is at."

Since establishing itself, the stink bug has become a severe agricultural pest that feeds on over 300 different plants, including dozens of economically important fruits and vegetables. While it’s impact has been felt most dramatically in Mid-Atlantic states like Pennsylvania, New York, New Jersey and Delaware, Michigan’s own apples, peaches and nectarines are now at the mercy of the bug.

"The problem with this insect is it eats everything," said Tracy Leskey, with the Department of Agriculture. "It’s hard to kill, it’s a big insect, it’s very mobile and has a lot of dispersal capacity."

Very few studies have actually quantified the economic damage of it. Leskey said studying damages can be difficult because of how quickly crops can be damaged and die. One 2010 study conducted by the American/Western Fruit Grower did find a $37 million loss in apple yield in the mid-Atlantic. Szucs also said an MSU study found farmers near Grand Rapids reported invasive stink bug damage to 60 percent of their yield early in the season to the pest - and damage to 30 percent of them at the end of the season.

"They are very difficult to control with chemicals," Szucs said. "They (pesticides) are super ineffective in damaging them"

When the stink bug eats, it largely avoids any pesticide sprayed on the surface of the plant and crop because of its syringe-shaped mouth it uses to eat and the stilts it uses to stand on. Both buffer the insect from the poison.

This combination has made pushing back against the bug particularly difficult. Enter: Trissolcus japonicus.

If you’ve heard of it before, it was probably by a more informal name: the samurai wasp. Up-close, this insect exhibits many nightmarish characteristics one would shutter at the thought of seeing fly across their yard. Except they’re small, like fit under your finger nail small - the perfect size to invade an invasive stink bug’s egg.

"It’s adapted to BMSB (brown marmorated stink bug), it picks up on their chemicals and cues when the BMSB leaves," said Szucs.

It’s so well-adapted that between 80 to 100 percent of stink bug eggs in a group can be infected by the wasp.

It sounds like a disaster waiting to happen, introducing one foreign species to control another foreign species. If the first invasive species has created disaster for one segment of the economy, why would another not magnify the issue? Maybe it would target a different species or carry over some unknown disease. It’s why anytime researchers propose this method, it can take years to get approval. In the samurai wasp’s case, it wouldn’t matter.

That’s because while researchers were testing to see if the wasp could prove a viable control agent, it appeared in the wild on its own - most likely through the same means the stink bug did. It’s now spread to several countries.

In laboratory tests, researchers found wasps infected invasive stink bug eggs over native ones when given a choice between the two.

Since its discovery in Michigan in 2018, Michigan State researchers like Szucs have collected the wasps and released them into the wild. So far,  about 4,000 adult wasps and 88 already-infected egg masses around the state - mainly in places with heavy agriculture. They also placed native stink bug egg masses in similar areas where invasive stink bug egg masses were found. The results were similar to those in laboratory settings - a good sign for researchers.

As a biological control agent, the wasp can only be distributed in states where it appeared naturally and if the state’s agricultural department gives approval. When given approval, the wasp has proven a resilient defense against the invasive stink bug,

"TJ has a huge role to play," Leskey said. "We’re seeing in the Mid-Atlantic, where we’ve seen TJ for a number of years, we are seeing the populations (of invasive stink bug) decline."

The invasive stink bug problem isn’t only a problem here either. New Zealand has already approved releasing the insect into the wild and there’s a petition in Canada to do the same.

"The thing about the wasp, it can take years to build up large enough populations," said Szucs.

Once that day is achieved, researchers hope the invasive stink bug’s populations are restored to a balance seen in its native countries. Szucs said any effort to completely eradicate the bug’s numbers in the country would be moot - it’s here to stay. That’s why efforts are now in place to control the population.

"In biological control, usually eradication doesn’t happen, but the balance is restored," Szucs said. "They will always exist in the U.S., they won’t go away now. But hopefully we’ll keep its numbers down."