Bug versus bug

By Mary Elizabeth Williams-Villano

Scientists are fighting one invasive insect with another invasive insect.

Brown marmorated stink bug
Susan Ellis, Bugwood.org

An invasive insect may have finally met its match — another invasive insect. According to a FOX 2 Detroit news report, scientists are finding success siccing one bug on another one.

Get ready for the grudge match of the century: in this corner, out of Japan, it’s Halyomorpha halus, commonly known as the brown marmorated stink bug. In the other corner, also out of Japan, it’s the challenger, Trissolcus japonicus, a.k.a. the samurai wasp. The BMSB can’t be happy about facing this opponent.

Not a looker, this hairy flying wasp has two wacky-looking antennas, big, scary eyes and iridescent orange legs. But it’s not frightening because of its looks. This tiny bug, small enough to fit under a fingernail, just happens to be the BMSB’s natural predator.

Don’t judge the samurai wasp by its small size. Even though the BMSB is much larger, this wasp’s teensy-ness is its secret weapon: it’s tiny enough to tunnel into the stink bug’s eggs and devour the innards.

The story of this rivalry begins somewhere back in the 1990s, when the BMSB is believed to have come here as a packing-crate stowaway from Japan or China. It stopped first in Pennsylvania and has since been on a marathon road trip. Not having a native predator to keep it in check, it’s traveled to 44 states so far.

This invasive stink bug has done more than annoy homeowners during the winter. Since establishing itself, BMSB has become a severe agricultural pest that feeds on over 300 different plants, including dozens of economically important fruits and vegetables. Its impact has been felt mostly in the Mid-Atlantic states -- Pennsylvania, New York, New Jersey and Delaware. But Michigan agricultural officials are worried about the bug targeting the state’s apple, peach and nectarine orchards.

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

To add insult to invasion, the BMSB is “very difficult to control with chemicals,” Szucs is quoted as saying. “They (pesticides) are super ineffective in damaging them.” That’s because of the manner in which it eats: its syringe-shaped mouth and stilt-like legs allow it to feast with impunity, without coming into contact with any pesticide that might be sprayed on the surface of the plant.

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

Frustrated for years, entomological researchers experimented to see how effective the samurai wasp is in killing the BMSB. The early results have been promising.

Usually, when scientists propose introducing one foreign species to control another, it can take years to get approval because it raises fears that the insect intended as the control might also target another, more beneficial bug, or be a vector for some unknown disease.

In the samurai wasp’s case, though, those concerns are moot. While researchers were doing those experiments, it appeared in Michigan in 2018 on its own. It’s more than likely that it got here the same way its prey did, via international shipping. It’s now spread to several countries.

In laboratory tests, researchers found the samurai wasps chose invasive stink bug eggs over native ones when presented with a buffet that included both. “It’s adapted to BMSB, it picks up on their chemicals and cues when the BMSB leaves,” Szucs says in the story. It’s so well-adapted, in fact, that between 80 to 100% of stink bug eggs in a cluster can be infected by the wasp.

Since the wasp’s discovery in the U.S., Michigan State researchers like Szucs have been collecting the wasps and releasing them into the wild. So far, they’ve distributed 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 areas where BMSB egg masses were found. The results were similar to the ones in the laboratory settings.

As a biological control agent, the wasp can only be distributed in states where it’s appeared naturally and where the state’s agricultural department gives its approval. In those places, the wasp has proven a resilient foe for the BMSB.

“This wasp has a huge role to play,” Leskey told FOX 2 Detroit. “In the Mid-Atlantic, where we’ve seen it for a number of years, we are seeing the populations (of invasive stink bug) decline.”

Looks like the little guy is winning. For the sake of our fruit trees, let’s hope so.