With a score of hosts available to spotted wing drosophila, cherry growers must manage their orchards to keep ahead of the pest throughout the growing season.
This is why non-crop hosts of the pest are a major focus of Dr. Howard Thistlewood, entomologist with Agriculture and Agri-food Canada at the Pacific Agri-food Research Centre in Summerland, British Columbia, Canada.
“It builds year-round, so we look at what it does outside the crop, in the rest of the environment,” he said.
The fly, native to Asia, was identified in strawberry fields around Watsonville, California, in 2008 and in Oregon’s Willamette Valley and British Columbia’s lower mainland the following year.
It is now widespread across fruit growing regions of Canada and the United States and is a particular challenge for berry and cherry growers.
Unlike other fruit flies, which typically infest damaged fruit, spotted wing drosophila is equipped with a saw-like ovipositor that allows it to deposit eggs in undamaged fruit.
But if spraying can provide effective fly control, it’s also among the least favored options because many export markets have low tolerances for pesticide residues.
Understanding how the pest behaves is key to determining if sprays are even required.
Among the fascinating discoveries that Thistlewood and colleagues in the United States, including Dr. Peter Shearer, entomologist with Oregon State University, have made is that the fly transforms into a different, tougher critter as temperatures drop and daylight diminishes.
“It’s actually a different kind of fly in the winter,” Thistlewood said. “It’s a different color, different size.”
But as the days lengthen and temperatures rise, it emerges from its overwintering locations in search of the nourishment that allows it to reproduce and multiply.
“In the coastal situation, that’s going to be the berries. In our situation in the interior, that’s going to be the cherries,” Thistlewood said.