A Tale Of Two Insects: How Samba Wasps, Spotted Lanternflies Could Impact Local Farmers

Insects can be friends or foes to local farmers, whose crops depend on healthy pollinators but can be wiped out by a single pest species. That paradigm is on full display in northern Michigan, where potential good news is emerging in the form of a wasp that could combat the local fruit-destroying spotted wing drosophila – even as experts closely monitor another emerging threat, Michigan’s first appearance of the spotted lanternfly.

Spotted wing drosophila (SWD), a fruit fly originally from Asia, has been the bane of Michigan farmers since it was first detected in the state in 2010. Unlike other vinegar flies that target damaged fruit, SWD infects healthy fruit, with females cutting a slit in the skin and laying their eggs. The larvae then feed within the fruit, causing brown, sunken areas to emerge. SWD target a variety of soft-skinned fruit, including raspberries, blackberries, blueberries, strawberries, grapes, plums, and cherries. Compounding issues, the insect has a rapid developmental rate – it can complete a life cycle in a week and produce up to ten generations a year – allowing its populations to quickly multiply and inflict severe crop damage.

Now widespread in the state – it’s been detected in every county in the southern peninsula where it’s been monitored – the insect can wreak widespread havoc on farms. In 2019, an estimated “30 percent of Michigan’s tart cherries in the northwest region of the state were destroyed due to a zero-tolerance policy for detectable SWD larvae,” according to Michigan Farm Bureau. In addition to losses from crop failures, the insect has also driven up preventative costs for farmers, whose only effective remedy for SWD to date has been pesticides.

“In high pressure years, it feels like we’re spraying all the time, and you still have to constantly worry about the pests breaking through the spray program,” says Isaiah Wunsch, Peninsula Township supervisor and a sixth-generation farmer who serves as CEO for the Old Mission-based Wunsch Farm. “In breakthrough events where SWD surges, we don’t have a whole lot of native predators for the pest. There’s nothing in the environment that keeps the population in check.”

But that could soon change, as Michigan State University researchers explore a new weapon to combat SWD in the form of another Asian insect: the samba wasp. This month, northern Michigan became the first of two spots in the state selected for an experimental release of the tiny parasitic wasp – which lays its eggs in SWD larvae – into local orchards. MSU Extension Specialist and Northwest Michigan Horticultural Research Center Coordinator Dr. Nikki Rothwell says 500 wasps were recently released on three Leelanau County cherry farms. Another colony was released last week in blueberry fields in southwest Michigan. The goal? To monitor the samba wasp’s population growth this and next year – including their ability to successfully overwinter in Michigan – and see whether they can have a measurable impact on local SWD numbers.

“This is a long time coming,” explains Rothwell. “It seems like it’s short because we just did the release recently, but this has been in the works for over 15 years.” According to MSU Extension, it took over a decade of permit reviews before the U.S. Department of Agriculture (USDA) and Michigan Department of Agriculture and Rural Development (MDARD) approved the release of the samba wasp in regions where fruit production is threatened. That’s because while biocontrol – the use of living organisms to control pests – can often be a highly effective tool in integrated pest management, it has at times produced unintended consequences (a famous example is the release of cane toads in Australia). In this case, however, Rothwell says samba wasps were evaluated extensively before receiving approval to be released.

“We’re not just releasing any old wasp,” she says. “We’ve taken great precautions. It only preys on SWD. It doesn’t affect our native fruit flies, and we didn’t release very many. The thing that’s really good about this from a farming and environmental perspective is we’re hoping this will reduce the amount of pesticides needed (to control SWD).” If initial experiment results prove promising, MSU Extension could dedicate more research to successfully growing and managing colonies in labs and introducing those colonies to local farms. “We just started on a small scale with three grower cooperators, but if successful we could move things along to different parts of our area for cherries and blueberries,” says Rothwell.

That would be welcome news to Wunsch, who says he and other Old Mission farmers are increasingly exploring ways to move away from pesticides and toward more organic and minimally sprayed crops. SWD poses a compounding problem in that as some farmers retire early or leave the profession – in part because of devasting pests like SWD – their abandoned orchards can become breeding grounds for the insects, which then spill over onto neighboring active farms, Wunsch says. Without effective controls outside of pesticides, SWD “has been a big challenge in moving those sustainability objectives forward,” he says. But a biocontrol agent like samba wasps could be a promising solution. “A parasitic predator, as long as it doesn’t have other environmental risks, seems like a really good way to keep them under control,” Wunsch says.

Even as researchers tackle the SWD, they’re keeping their eye on another potential insect threat to Michigan crops. On August 10, Michigan’s first recorded detection of the spotted lanternfly was confirmed in Oakland County. The distinctive invasive species from eastern Asia was first found in Pennsylvania in 2014 and has since spread to 13 states, including Michigan. According to MDARD Communications Director Jennifer Holton, it’s an “ongoing and open investigation” as to how spotted lanternfly arrived in Michigan, though she says it was likely through “infested nursery stock, possibly several months ago.”

Spotted lanternfly feeds on a wide range of plants, including grapes, hops, black walnut, river birch, willow, sumac, and red maple. When feeding, the insect produces a sticky liquid called honeydew that can collect on the ground and surrounding vegetation. This results in the growth of sooty mold, which can discolor and kill plants. MDARD is in the “assessment stage of response, but it is important to note that typical pest management techniques have not proven effective for eliminating the pest in other states,” Holton says. With Michigan home to 10,900 acres of juice grapes and 3,375 acres of wine grapes – many of the latter concentrated in northern Michigan – Holton cautions that “there is the potential for spotted lanternfly to negatively impact Michigan’s grape industry.”

On a more positive note, Rothwell notes that only one specimen of the spotted lanternfly has been found so far in Michigan. She says researchers “aren’t panicking by any means yet, but are trying to do a good job monitoring this. We are always on the lookout for new invasives. This is just the newest one.” Michigan residents are encouraged to report any sightings of spotted lanternfly to the state and capture/destroy the insects (photographing them first is recommended for documentation purposes). Spotted lanternfly moves easily on firewood, tires, campers, and vehicles, so residents are advised to park with their car windows closed and check vehicles before moving them. The insects also gravitate heavily toward the invasive ailanthus tree, also known as “tree of heaven,” with homeowners encouraged to remove those trees from their properties.

Rothwell says pests like SWD and spotted lanternfly are just a few of the numerous challenges piling up for Michigan farmers, who are also struggling with climate change impacts, rising costs, and competition from foreign growers. Rothwell says local farmers “have been resilient,” but worries that mounting difficulties will continue to chase growers out of the industry. Finding effective solutions to invasive pests and other challenges will be critical to keeping northern Michigan’s agricultural industry alive for future decades, she says, “Every time we have a freak warmup or a hailstorm or a new pest, it’s hard for (the farmers) to handle,” she says. “Our job is to help find solutions. Maybe it’s different crops. Maybe it’s the diversification of a farm. We have to make sure growers can stay in business for the next generation.”

Pictured: Left, samba wasps in a vial at MSU; Right (top and bottom), the spotted lanternfly