Invasive fly found in N.L.

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Spotted wing drosophila annoying farmers in B.C., Ontario

Before this summer, it was the only Canadian province where the spotted-wing drosophila had not been identified. 

Scientists have confirmed that an invasive pest known to be a nuisance for farmers across North America has a presence in Newfoundland and Labrador. This photo of a male spotted wing drosophila was taken under a microscope. — Photo courtesy of Agriculture Agri-Foods Canada

Originating from Asia, the fruit fly-like creature first appeared in North America five years ago in California and its population has since spread west to east.

Where fruit flies pose a nuisance for overripe fruit, spotted-wing drosophila can lay eggs in fresh fruit, opening up the possibility of maggots appearing in harvested fruit at stores. Its ovipositor has little teeth that work like a saw to penetrate thin-skinned fresh fruit, including berries and cherries.

Last summer, the Atlantic Cool Climate Research Centre in St. John’s set up traps across Newfoundland in commercial farms and the wild, covering eight sites in all. Depending on the site, traps were checked every one to two weeks. According to entomologist Peggy Dixon, the fly was found “at most, but not all of them.”

“Most places that we trapped, we found it in very low numbers — one, two, three — certainly not hundreds or thousands,” said Dixon.

When the flies were identified, fruit samples were then taken from those sites where available (in some cases, the fruit was already harvested) to see if any produced flies.

“In some cases we got flies, which means that when we collected them, the eggs or larvae were in the fruit breeding.”

According to Dixon, research conducted elsewhere has shown that spotted wing drosophila tend to spend the winter in sheltered areas before becoming active in the spring.

For commercial farms, traps were set up in both the fields and the nearest wild fruit-bearing hedgerows. Dixon said most spotted wing drosophila samples at commercial farms were taken from hedgerows.

 

Widespread in B.C.

According to British Columbia’s Ministry of Agriculture, spotted wing drosophila are now widespread in coastal and interior fruit-growing areas of that province. Surveys conducted by the Ontario Ministry of Agriculture and Food in 2013 detected its presence in 90 per cent of monitored sites. The year before, that figure was 60 per cent.

Dixon said there was no anecdotal evidence from farmers related to local crops having been compromised.

“If they can (survive) over winter and the population increases and increases as we’ve seen in some other areas, like Ontario and Nova Scotia, then we’ve got an issue. But so far, no, there was no anecdotal evidence at all of food quality being compromised because there were maggots inside or anything like that.”

With respect to dealing with the invasive pest, there may be a couple of factors working in Newfoundland and Labrador’s favour.

“In one sense, we’re fortunate that it moved from west to east,” said Dixon. “We can piggyback on what (other jurisdictions have) done. We don’t need to reinvent the wheel.”

A short-term solution on the table is the use of insecticides. Dixon said there has been an emergency registration of insecticides for suppression purposes in all 10 Canadian provinces. A document on the Ontario Ministry of Agriculture and Food website identifies Ripcord insecticide as one such option. Dixon said there are also non-chemical alternatives being developed.

Farmers may choose to change harvesting practices by doing so on a more frequent basis in order to limit crop exposure to spotted wing drosophila. Dixon said scientists are also looking at what parasites in Asia work to keep the spotted-wing drosophila population in check.

“There’s a lot you have to go through,” she noted. “Even if (the parasites) work, you have to make sure it doesn’t affect anything native.”

Dixon also notes there are provinces in Canada where spotted-wing drosophila were identified one year but not in subsequent years.

“The thing about here is, we don’t know if they’re going to successfully (survive) winter,” she said. “When you think about the theory that allowed them to spread so quickly — the theory’s that they’re moving around on shipments of berries into supermarkets and people are taking them home — it seems to be human activity, accidentally, that’s moving them around.”

Once the snow melts and weather begins to warm, traps will once again be set up to see if spotted-wing drosophila return. Dixon expects more sites will be monitored in 2014.

Organizations: Atlantic Cool Climate Research Centre, Ontario Ministry of Agriculture and Food

Geographic location: California, Ontario, Newfoundland and Labrador North America B.C. British Columbia Nova Scotia Asia Canada

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