OSU scientists to release parasitic wasp after 12 years

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June 10, 2022

 Photo: Dr. Kent Daane, University of California, Berekley.

A tiny wasp attacks invasive spotted wing drosophila. Photo: Dr. Kent Daane, University of California, Berekley.

A parasitic wasp that controls a highly destructive fruit fly will be released in June after 12 years of research by Oregon State University (OSU) agricultural scientists.

Dr. Vaughn Walton, an extension entomologist and professor in the OSU College of Agricultural Sciences, said the U.S. Department of Agriculture has permitted the release of the wasp (Ganaspis brasiliensis), a slow process that took more than 10 years from application to decision, according to an OSU news release.

Now that it has a permit, the lab, which is part of the OSU Agricultural Experiment Station, is raising enough wasps to make a dent in the spotted wing drosophila(Drosophila suzukii,or SWD) population in Oregon.

An invasive insect from Southeast Asia, the spotted wing drosophila arrived in Oregon in 2009. It soon became a major pest of soft fruit crops, such as cherries, peaches, figs, blueberries, strawberries, blackberries and winegrape.

Damage from the invasive insect cost the country’s agricultural industry approximately $500 million a year. The insect especially has an affinity for blueberries, which is Oregon’s ninth-most valuable crop at $120 million in 220. Management of spotted wing drosophila in the blueberry industry alone cost growers about $100 million a year nationwide.

“This will have a huge impact,” Dr. Walton said in a news release. “Spotted wing drosophila is very difficult to control. It’s got a very, very high reproduction rate with many generations per year. Because of that, when using pesticides, they have to be applied constantly, sometimes two or three times a week. Growers are really interested and are excited about a biological control that will work along with cultural management tools to decrease SWD and not cost them any money. It’s a natural resource available to them. We think this is going to change things.”

An integrated pest management (IPM) approach that uses cultural controls like good sanitation, proper pruning, drop irrigation and weed cloth can be somewhat effective. IPM program still need the addition of pesticides to fight spotted wing drosophila, Dr. Walton said in a news release.

“The wasp helps, but you must do the other things as well,” said Dr. Walton, who led the team that discovered the wasp in South Korea, one of its native habitats. “None can stand on its own. I had a call from a grower who was doing everything right and he wanted to know if he could spray less pesticides. Even removing one application is a significant cost savings – $150 an acre. That’s a lot of savings if you do all these things together.”

Spotted wing drosophila, a tiny fruit fly that resembles those that hover over rotting fruit in summer, is well-suited to the Willamette Valley climate. About 95 percent live in areas surrounding non-crop habitats that act as pest reservoirs for reinvasion of the crops. That’s where the wasp will be released.

The adult female fly lays her eggs – up to 600 per year – within ripening fruit, said Ryan Chave, a graduate student who works with Dr. Walton. When the larvae emerge, they burrow in and start eating the fruit from the inside out, causing damage that results in severe crop losses.

“The parasitoid wasp kills spotted wing drosophila by laying eggs inside the insect and when the wasp hatches, its larva consumes its prey,” Chave said in a news release.

Spotted wing drosophila populations can be kept at a bay at a rate of up to 65 percent when the parasitoid wasp is there to check it, according to preliminary data.

“We’ll never take down the entire fly population,” Dr. Walton said in a news release. “But as spotted wing drosophila increases there’s more food for the wasp. In the field if you have a bunch of spotted wing drosophila attack a crop and reproduce, as they increase there it gets larger and larger.”

Though not native to Oregon, a few of the parasitoid wasps were found in Oregon and allowed the researchers an opportunity to study them in the field. They’re confident it will not become an invasive pest problem since Ganaspis brasiliensis is a specialist – in other words it only feeds on spotted wing drosophila, said Dr. Walton, who worked closely with Dr. Jana Lee of the Oregon Department of Agriculture. He also collaborated with colleagues at University of California, Berkeley. Dr. Walton has studied another Asian wasp (Pachycrepoideus vindemmiae) that has promise but not as much as G. brasiliensis because it’s a generalist and will kill other insects in addition to spotted wing drosophila.

Have you ever encountered SWD in a residential or commercial account? Tell us about it in an email to pmpeditor@northcoastmedia.net.

About the Author

Ellen Wagner

Ellen Wagner is the digital editor for PMP magazine. She can be reached at ewagner@northcoastmedia.net.

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