Spotted wing drosophila fruit fly causing havoc for B.C. cherries

An invasive fruit fly species that feasts on cherries and berries before they ripen is on the rise this year across B.C. because of the warmer weather.

The spotted-wing drosophila first showed up in B.C. over five years ago, and has quickly become a threat to crops — especially cherries.

"People think of the vinegar [fruit] fly that appears in late summer on our soft fruit when we bring your peaches in. This one is very similar to appearance to it," said Hugh Phillip, a retired entomologist in the Okanagan.

"But unfortunately it doesn't wait until the fruit is overripe or damaged to attack the fruit, which is what makes this particular pest so insidious."

This difference means the flies can ruin fruit before it is ripe.

"We used to say for the old vinegar fly, 'Get the fruit off the tree once it's ripe and you're safe,' but with this particular one that's not the case."

"The females lay several eggs and the small maggots basically digest the pulp of the berry or cherry and renders it kind of brownish as if it was damaged or diseased ... and in most cases inedible."

According to Phillip, the spotted-wing drosophila originates from Asia and arrived in B.C. via California in 2008. It's since spread across North America within a couple of years.

"It's one of the fastest spreading invasive pests that we know of," said Phillip.

Warmer weather a problem for cherries

This year has been a particularly prosperous one for the invasive species. Phillips notes that due to several factors including the warmer conditions, the flies have been able to multiply exponentially.

"In the past, the pest has gradually increased in numbers over the summer and not really created a problem until mid-August. This year the numbers are at levels that we normally don't see for three or four months already in May."

He says the main crop affected is cherries.

"Growers must be on guard right from the time cherries start to turn straw coloured and basically protect their crop."

"For homeowners that have cherry trees or berries that harbour the pest, they have to do everything they can to not create pest problems for their neighbouring commercial growers."

Because there are very few chemicals available to the average gardener for use in ridding themselves of the flies, Phillips says drastic action is often needed to nip the problem in the bud.

"I strongly recommend if they don't want to spend the time spraying weekly or every 10 days to protect their berry crops, they either take the tree down or get a professional pest control operator to apply the products."

An uncertain future

He acknowledges that it's hard to predict the long term impact of the species, but says a lot relies on what scientists come up with in terms of crop protection tools.

"Recent research has indicated there is a fruit extract that has proven to be very repellent to the adults flies. This is pretty exciting news. It might not be 100 per cent, but it would certainly provide a safer alternative to chemicals and also provide homeowners [an option] to provide their own protection."
 

To hear the full interview, click the audio labelled: Invasive species threatens B.C. backyards.