Research Update
Search on for natural enemy
Agassiz researcher working to find a predator to help combat spread of SpottedWing Drosophila.
By Judie Steeves D
avid Gillespie is optimistic that it’s only a matter of time before discovery of a biological control for the dreaded Spotted Wing Drosophila.
A research scientist and
entomologist at the Pacific Agri-food Research Centre in Agassiz, Gillespie has been working to understand what is interested in eating SWD in fields, orchards and hedgerows.
SWD is a vinegar fly that infests ripe (not rotten), soft-skinned fruit such as cherries, berries, apricots, plums and peaches, rendering it unfit for market. It’s native to Asia and was first discovered in the Pacific Northwest in 2008. By the next year populations had grown so rapidly whole crops had to be abandoned and in 2010 it was discovered infesting crops in both the Fraser and Okanagan Valleys. “It takes a relatively long time for the generalist community to respond to new prey. There’s a learning curve while they discover that there’s new prey available,” he explains. However, SWD do get caught up in spiderwebs, and are consumed by jumping spiders, beetles and earwigs. But in order for existing predators to take on new prey they must switch strategies to be successful in the hunt for food.
CONTRIBUTED PHOTO
Researcher and entomologist Dave Gillespie at the Pacific Agri-food Research Centre in Agassiz.
Because SWD lays eggs inside intact fruit, instead of outside rotting fruit, the vision and odour used to locate pests attracted to yeasty, rotting fruit found on the floor of the orchard must change for a predator to be able to find the new vinegar fly, SWD.
“It’s quite different from looking at sound fruit up in a tree,” explains Gillespie.
However, he is also rearing some parasitoids from SWD and feels there is promise that down the road they might prove to be a control for the devastating new insect pest of soft fruit.
“We do have the potential to mass-rear some parasitoids,” noted Gillespie.
Scientists in the U.S. are looking at some Asian parisitoids, since Asia is where SWD is native.
We may also have to look overseas for a predator, but we are slow and reluctant to bring in new critters, he says.
The other possibility is bacteria. “We all pack bacteria around with us and fruit flies are no different,” he notes. “I don’t think it will take too long to find something to combat it.” First, Gillespie is surveying what’s out there, and in the coming year he hopes to get a sense of where to find predators and what their impact might be on SWD populations.
“We also need to understand what
lures them through all four seasons,” he explains.
It’s important to know what the natural enemy community is doing and when.
Since cool weather obviously slows SWD down, that appears to be a promising time to tackle populations, while they are down.
It’s one thing if only 100 survive winter, but quite another if 1,000 survive.
Perhaps hedgerows can be manipulated to make them less suitable, if that’s where they overwinter.
It does seem important to manage the border areas around the farm. Gillespie expects the insects look for leaf litter in which to overwinter. That’s good for his work, because there are lots of predators in such habitat. Perhaps ground beetles or earwigs could be encouraged.
“There are lots of possibilities,” he says.
Birds and mice might also go for the adult flies, particularly in winter, but it’s important to find out how SWD survive winter and what kind of conditions help them survive the cold. Not enough is yet known about SWD to say which strategy will work best to manage their invasion into orchards, Gillespie says. But, he’s working on it.
British Columbia FRUIT GROWER • Winter 2011-12 19
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