How A Tiny Wasp Could Help Fight Back Against Berry Pests

by | Jun 9, 2023

There’s nothing better than a fresh North Carolina blueberry or blackberry on a warm North Carolina day. 

Unfortunately, humans aren’t the only species that think that.  

An invasive species of fruit fly, Spotted Wing Drosophila (Drosophila suzukii, SWD), poses a looming threat to North Carolina’s delicious berry crop. 

Spotted Wing Drosophila on a berry.

Unlike native fruit flies, which lay eggs in fruit that is already overripe and rotting, SWD burrows into the soft flesh of immature berries and lays its eggs as the fruit is ripening, ruining the fruit. A single SWD larva in the fruit can cause rejection of an entire shipment, leading to high financial risk for farmers of impacted crops. 

Luckily, work taking place at the NCDA&CS Plant Industry Division’s Beneficial Insects Lab is moving us closer to protecting North Carolina’s berry crops from the risks of SWD. 

A species of wasp, Ganaspis brasiliensis (Gb), is a natural biological control to check the growth of SWD and may be one part of a solution to keep North Carolina’s berry harvest strong. The USDA approved Gb for release and further testing in 2021. 

If you have a fear of wasps, fear not. This species is less than two millimeters long and doesn’t have a stinger. It poses no threat to humans or animals other than SWD and doesn’t even really resemble a popular conception of what a wasp looks like. 

A Gb wasp. Photo: Washington State University.

Gb lays its eggs in the very young SWD larvae already inside the fruit and the growth of the Gb larva consumes the SWD larva, killing off the SWD. The fruit has already been ruined, but future generations of SWD are eliminated by a healthy colony of Gb, which protects future fruit crops. 

“This is a new biological control. We’ve been working on it for a couple of years now,” said Martha Flanagan, a Research Scientist at the Beneficial Insects Lab. “Last year, we did release at Ag research stations that are a partnership between N.C. State and Ag. We did those releases at three research stations across the state: Sandhills, Piedmont and Mountain Horticultural Crops Research Station. That was our first experimental release. This year, we’re going to continue to do releases to see if we get establishment of these wasps and help control the SWD.” 

Last year’s releases were quite small.  

A total of approximately 500 wasps were released at each of the three research stations – too few to make a meaningful difference against SWD, which can lay 300 eggs per female. A few times after the wasps were released, researchers went back to see if any wasps were present to be recovered. None were. 

The hope, though, is that more wasps can be released this year and begin to establish colonies on their own. A fourth location – Horticultural Crops Research Station — will have wasps released this summer.  

“The goal is to see some recovery,” Flanagan said. “We’ll release over the summer and then we’ll go back in the fall to look at fruit and see some wasps that hopefully are the progeny of the wasps we released. We’re in our field season now, so we want to get enough wasps available to release on-site. I’m trying to build up the wasp population. Crops across the state mature at different rates, so within a couple of weeks, I need to be able to release some number of wasps at our Sandhills site. Maybe a week or two after that, I’ll need more ready for release at our Piedmont and Mountain sites and we’ll want to do multiple releases over the course of the season, so we’re very focused on having enough wasps to release.” 

If Gb colonies can establish themselves and decrease the presence of SWD, benefits will include higher yields with less fruit lost and a lower cost of production for farmers. 

“Before SWD got into our blueberries, blueberries had a lighter pest load than some other crops,” said Gregory Wiggins, PhD, a Biological Control Administrator at the lab. “They didn’t require a lot of treatments for things. Now, because of SWD in berry crops, sometimes at the peak of the season, growers have to apply pesticides maybe every 6 to 10 days. If that crop is one of the later progressing crops in the season, over the course of that season, you might be applying pesticides maybe 16 times to that one crop.  

“Our hopes are that if we can learn more about this wasp after we release it, it can establish and we can learn how to better disperse it to make sure it’s established in growers’ fields, it will lessen the pest load for berry crops and require fewer pesticide applications, lowering the cost input. 

More fruit produced at a lower cost to the farmer with fewer pesticides means lower prices for consumers with more organic produce available. 

The Beneficial Insects Lab proves that while insects are often a problem for agriculture, they can also be the solution.