Samurai wasp may be helpful invasive species

In 2018, researchers at Agriculture Canada’s Agassiz Research and Development Centre discovered the presence of the samurai wasp for the first time in Canada.

But the arrival of this invasive Asian insect might not be a bad thing.

The tiny wasp lays its eggs inside the eggs of another invasive species from Asia, the destructive brown marmorated stink bug, which feeds on fruit trees, hazelnuts and berries.

They are also a contamination issue for grape growers because the presence of a few adults at crush can taint wine.

As hitchhikers in shipping containers, packaging materials, cargo and vehicles, the marmorated stink bug and the samurai wasp have been moving in tandem around the world.

The stink bug first showed up in North America in Pennsylvania in 2001 and has since spread throughout the United States, feeding on more than 100 plant species. In 2010, the apple industry in the mid-Atlantic states reported an estimated loss of US$37 million due to marmorated stink bug invasion.

In Canada, the stink bug arrived in Ontario six years ago and in British Columbia in 2015. Now it is in the Fraser Valley, Brentwood Bay on Vancouver Island, and the Okanagan Valley with high numbers present in the Kelowna area.

According to B.C.’s Ministry of Agriculture, the bug is shield-shaped with a brown marbled appearance, white markings on the outer abdomen and white bands on the last two antennal segments. The samurai wasp is black, about the size of a sesame seed and with an exoskeleton. It has a point where a wasp’s stinger would normally be but which is used to lay its eggs inside the stink bug’s eggs.

“The brown marmorated stink bug invasion in Canada is still in its early stages,” said Paul Abram, a research scientist with Agriculture Canada. “We have not observed any agricultural damage in Canada up to this point, but we do see that populations of the pest are building and the bug is now widespread across the Lower Mainland and the Interior regions of B.C. Our research group, along with provincial entomologists and co-operating growers, are keeping a close eye on whether it will move over into crops in the coming years.”

He said that elsewhere in the world, severe economic agricultural damage begins about seven to 10 years after the insect gets established.

“Once the damage starts, large losses measured in the tens of millions of dollars have been observed in tree fruits and nuts in northeastern U.S.A. and Europe.”

Much of the research at the Agassiz centre has focused on whether natural Canadian enemies of invasive agricultural pests will attack and control populations. This involved field surveys to monitor established pests and see what could be attacking them.

“The goal of this particular survey, which we started in 2017, was to see what native parasitoid wasps attack the eggs of the brown marmorated stink bug,” he said. “We did find three species of native parasitoids (which normally parasitize on native stink bug species) that attempted to attack the eggs of the invasive stink bug but were unsuccessful at doing so. Because we knew that the samurai wasp was already established in Washington state, there was a chance we would eventually find it in British Columbia. But we were a little surprised that it turned up so soon, in only the second year of our surveys.”

According to the research paper co-authored by Abram, 28 samurai wasps emerged from a brown marmorated stink bug egg mass from a site heavily infested by the bugs in Chilliwack, B.C., in 2018.

What invasion route the stink bugs and wasps took, though, is still a mystery.

The samurai wasp poses no danger to humans, other animals or plants.

In the U.S. and Europe, where the samurai wasp has not yet made an impact and where the brown marmorated stink bug is causing major crop damage, insecticides are the primary control method. Northeastern U.S. apple producers have increased insecticide use fourfold since the stink bug established itself.

In Canada, currently, there are a few products registered for suppression of the stink bug in tree fruit, but nothing registered for control.

“The main finding is that, while the samurai wasp can only attack stink bug eggs, it has the ability to attack the eggs of some species of native North American stink bugs but at lower levels than that of the stink bug,” said Abram. “The native stink bugs it can attack are occasional agricultural pests while some are considered potentially beneficial.”

Researchers are studying the indirect ecological effects of a new species coming into Canada that propagate through food webs.

“The anticipated ecological impact of the samurai wasp, should it establish, is likely to be limited but nonetheless complex,” said Abram. “(Our team) and several other research groups will be studying this in the coming years.”

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