Scientists study wasps that may protect British Columbia’s berries

Every year, invasive insects gnaw on Canadian farms, gardens and wild plants, spreading disease and disrupting ecosystems.

But tiny wasps that lay eggs that burst into invasive insects could potentially help berry growers in British Columbia protect their crops.

“It’s like nature is giving us a free service to help control crop pests,” said Paul Abram, a researcher with Agriculture and Agri-Food Canada who studies what happens when the insects are released into ecosystems in British Columbia.

Abram is one of the researchers studying how different species of parasitic wasps can control invasive pests across Canada.

Invasive flies

Spotted-wing drosophila, a small species of invasive vinegar fly native to Southeast Asia, lays eggs in soft fruits such as cherries and raspberries, causing them to rot prematurely. The species was first spotted in North America in 2009 and has since spread across the continent.

Little research has been done on the impact of these flies in Canada.

An investigation, in the Journal of Economic Entomologyfound that in Maine the spotted-wing drosophila can cause yield reductions of as much as 30 percent in blueberries.

Another study, published in the Journal of Integrated Pest Management, found that of 82 raspberry growers surveyed in Minnesota, the average yield loss due to flies was about 20 percent.

The BC Climate Change Adaptation Program, a collaboration of agricultural organizations, producers, researchers and the federal and provincial governments, lists the plague classified as a “major threat” on its website.

This isn’t just a problem for humans. Entomologist Chandra Moffat of Agriculture Canada said the flies also target wild berries, which are a food source for wildlife.

According to Moffat, the solution could be to bring the natural enemy of the suzuki fruit fly to Canada.

“One of the mechanisms that really makes it so invasive is that it’s separated from its natural enemy,” Moffat said. “We’re really working to reunite the invasive pest with its natural enemy from its native range.”

Ronin and samba wasps

Meet the ronin and samba wasps, two species of wasps native to China, Japan, and Korea. They find the tiny vinegar flies and lay their eggs inside the fly larvae. The wasp eggs wait until the larvae form a cocoon-like structure called a pupal case, and then they strike.

“They eat the whole inside of the fly,” Abram said. “Then they develop into a wasp and burst out, just like the chest-bursting alien [from the movie Alien] from the fly’s pupal casing.”

The wasps do not attack humans nor do they lay eggs in their homes.

Like their hosts, ronin and samba wasps have inadvertently reached BC. In 2019, Abram went looking for the suzuki fruit fly in a raspberry field near Agassiz, BC. There, he was surprised to see the tiny ronin and samba wasps flying around the fruit.

Both wasps were found to kill an average of 13 percent, and in some cases even 53 percent, of Asian fruit fly larvae.

Allan Carroll, a professor of insect ecology at the University of British Columbia, said wasps could be a valuable alternative to pesticides.

“If we can control the population in this way so that no more damage occurs and we no longer have to use chemical insecticides, then I consider that a victory for the environment,” he said.

According to Moffat, many parasitic wasps can only survive on one insect species.

“They can’t just choose another insect species because they’ve evolved so closely with the insect they’ve been living on for millions of generations,” she said.

Abram noted that ronin wasps also attack two other species of vinegar flies, while samba wasps specifically target the suzuki fruit fly.

Control of invasive species

The wasps are part of an arsenal of parasites that researchers are studying for pest control purposes.

Some wasp species are already being used to control aphids, preventing the spread of the blueberry-destroying scorch virus. Farmers can buy cardboard squares covered in wasp larvae, which they can hang in greenhouses to protect their berries.

According to Abram, parasitic wasps can also be placed in cardboard boxes the size of a golf ball, which can then be distributed across a field by helicopter or drone.

Abram’s team is still years away from delivering ronin and samba wasps to farmers, he said. They’re still testing how these wasps fit into the bigger picture of British Columbia’s ecosystems — and what happens if the spotted-wing drosophila population is suddenly reintroduced to Canada.