Detecting a pesky pest

Andrew Robinson
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Fly in every province except N.L., part of Farm Field Day in St. John’s

This spotted wing drosophila, as seen under a microscope, can be identified as male due to the presence of spots on its wings. — Photo courtesy of Agriculture Agri-Foods Canada

By Andrew Robinson

The Telegram

The spotted wing drosophila first appeared in North America five years ago in California. Since then, the invasive pest has spread throughout North America. It has now been identified in every Canadian province, excluding one — Newfoundland and Labrador.

“It’s quite amazing the speed that they’re actually spread around the continent,” said entomologist Peggy Dixon.

A display focused on how researchers are trying to determine whether or not the fly has made its way to Newfoundland and Labrador will be one component of the annual Farm Field Day at the Atlantic Cool Climate Research Centre in St. John’s.

The free event is scheduled to take place Saturday, Aug. 10, starting at 10 a.m.

Originating from Asia, spotted wing drosophila are comparable to fruit flies, but unique from those found in most kitchens in that they can lay eggs in fresh fruit.

Common fruit flies only do so in fruit that’s overripe.

“Those are a bit of a nuissance if you’re got some fruit,” said Dixon of the common fruit fly. “They’re not really a threat to a farmer who is selling berries to the supermarket or customers on the side of the road, because they’re not going to be in that fruit unless they’re overripe.”

While common fruit flies can’t penetrate the skin of fresh fruit to lay their eggs, spotted wing drosophila can. That’s because its ovipositor can work “like a saw” to lay the eggs into the fruit.

“It’s got little teeth on it, so it’s actually able to lay its eggs in fruit just before it’s ripe and when it’s ripe.”

This can lead to maggots turning up in harvested fruit found at stores. While there’s no harm in humans consuming such goods, Dixon said spotted wing drosophila represent a challenge to farmers looking to control the quality of their product. The invasive pest is already causing problems in the United States, British Columbia and Ontario.

“Any of these areas that grow a lot of fruit,” she said. “Mostly, it’s berries with soft skins.”

Dixon said staff at the centre made some attempts last year to try to detect its presence in Newfoundland, but the centre is making a bigger push in 2013 to find out if spotted wing drosophila have made it to the island.

Traps have been set up at commercial farms and in the wild. The centre is monitoring eight sites in all on a weekly basis, including some traps set up amongst berries growing on the centre’s fields.

The traps are made from red plastic cups — the colour is known to attract flies — with a cover on top and holes in the side. Inside the cups is a combination of vinegar and cider. Captured specimens are then examined under a microscope.

“They’re like the fruit flies in the kitchen, so they’re tiny, and there’s a lot of other species besides the one we’re looking for (in the cups),” she said.

The males have a big spot on each wing, while females do not. The latter are identified by teeth on their ovipositor.

As they are so new to the continent, questions remain as to how spotted wing drosophila need to be dealt with. Dixon said in Asia there are likely established predators and natural enemies to keep the species in check. That’s not the case in North America.

“When something comes in and it’s invasive like this, it’s coming in without (predators), so it’s out of balance.”

If spotted wing drosophila are found to exist in Newfoundland and Labrador, Dixon said the centre’s work will shift to identifying ways to help farmers deal with them.

Beyond the spotted wing drosophila display, Farm Field Day will feature other displays highlighting scientific work at the centre, a wagon ride through research plots, an activities tent where kids can make ice cream and plant lettuce, and a weather balloon launch.

Twitter: @TeleAndrew

Organizations: Atlantic Cool Climate Research Centre

Geographic location: California, Newfoundland and Labrador, North America Asia United States British Columbia Ontario

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