As part of a national team of entomologists studying the management of spotted-wing drosophila (SWD), the UC Cooperative Extension is reaching out to Central Coast Strawberry and Caneberry growers/PCAs regarding a survey on SWD Impacts. This survey will help us understand the current impacts of SWD on your farm and how these impacts may have changed in the last 10 years.
How will this information be used? This information will be used to develop new research goals as part of a USDA Specialty Crop Research Initiative proposal under development. It will also be compared to information collected in similar surveys in 2013 and 2014 to help us understand where challenges still exist for SWD management and what improvements have been made over the last 10 years and shared in extension and scholarly publications.
Who should I contact for more information? For more information about SWD management, contact Dylan Beal, djbeal@ucanr.edu, 831.294.9419, or members of our project team. For more information about this survey, contact Hannah Levenson, hklevens@ncsu.edu, 919.434.7882.
Spotted wing drosophila (SWD), a small fly native to Asia that first appeared in Michigan in 2010, isn’t like most pests. Populations of crop-damaging insects tend to have distinct generations. Not SWD. Several generations overlap and build through the year, attacking vulnerable agricultural crops and wild plants. The situation has created a major challenge for the Michigan berry and cherry industries.
Spotted wing drosophila in the lab.
Rufus Isaacs, a professor in the Michigan State University Department of Entomology, was one of the first to discover the pest in the state 13 years ago. While researchers didn’t know much about SWD then, they’ve had to get up to speed quickly.
Rufus Isaacs, professor of entomology at MSU.
“SWD is so destructive because it can insert eggs into ripening fruit,” said Isaacs, whose work is supported in part by MSU AgBioResearch. “Larvae can be present in harvested fruit, which can be a big problem for producers. It is also able to reproduce so quickly to build up the population, and it can infest wild fruit outside of farms, creating a reservoir population that continually invades crop fields after they’re treated.”
After hearing about SWD arriving in California in 2008 and then being detected in Florida in 2009, concerns began to mount.
“Shortly after SWD was found in Florida, I went to a conference in Oregon where we discussed measures we may need to take to get ready for the pest,” Isaacs said. “We expected it would be in Michigan before too long.”
Sure enough, Isaacs was right. He received a grant from Project GREEEN — a partnership among MSU AgBioResearch, MSU Extension and the plant agriculture industries of Michigan — in 2010 to monitor for SWD. Isaacs worked with members of the MSU Fruit Team to set small plastic traps with holes that were filled with a cider vinegar lure.
In late 2010, SWD was collected from a site in West Michigan. At that point, the difficult work began and persists today. Research in Isaacs’ lab has been performed in partnership with mostly blueberry and raspberry growers.
The team has tested already-registered pesticides to determine their efficacy, as well as non-chemical controls such as pruning, mulching and physical exclusion methods, where growers place netting around and on top of crops as they begin to ripen.
As a result of this research, online resources have been created to assist growers with SWD identification, pesticide timing and other management strategies.
“We want to ensure we’re responsive to grower needs, first and foremost,” Isaacs said. “That’s why the pairing of research and grower education programs through MSU Extension is so valuable to our team.”
Dennis Vander Kooi, a blueberry grower and owner of Woodland Enterprises Berry Farms in Zeeland, Michigan, and his family have been working with MSU researchers for many years. He is also a board member of the Michigan Blueberry Commission (MBC), helping to set research priorities for the industry.
“Rufus is one of the nation’s leading researchers on this issue, and we’ve worked with others at MSU as well,” Vander Kooi said. “He’s run several experiments on our farm, and we’ve learned a lot from them. The MBC has supported this work and will continue to in the future as we look for effective ways to manage this pest.”
Vander Kooi said the blueberry industry is undergoing a rejuvenation in Michigan, adopting newer genetics and planting varieties that meet the demands of today’s consumers. This, in conjunction with SWD, makes it a critical time for growers as they look to protect an industry that contributes nearly $132 million to the state’s economy, according to the Michigan Ag Council.
“With the creation of the MBC in 2017, we got the opportunity to start advocating for more dollars for research, and MSU has been instrumental in that,” he said. “To date, we’ve supported more than $390,000 worth of research, much of that going to MSU, and leveraged an additional $600,000 in other funding.”
In addition to the MBC, Project GREEEN has been a significant supporter of Isaacs’ SWD efforts, along with state funding through the Specialty Crop Block Grant program and national projects funded by the U.S. Department of Agriculture (USDA).
Assessing biological control options
One of the primary challenges for scientists is focusing on immediate grower needs while also investigating long-term management tactics. It’s a monumental task to balance both simultaneously.
Marianna Szucs, assistant professor of entomology at MSU.
Alongside Isaacs, Marianna Szucs, an assistant professor in the Department of Entomology, has been exploring biological control to reduce populations in the long run. As she noted, when SWD came to the U.S., its natural predators did not.
“Anytime there is introduction of an invasive pest, one of the main issues is that the new landscape doesn’t have natural enemies for it,” she said. “They don’t come with the pest, and the native insects in the new place aren’t equipped to deal with it right away. What we wanted to know is if we exposed parasitoid wasps native to Michigan to SWD, would they begin to see them as a food source?”
A parasitoid insect lays its eggs in or on a host insect, and the developing larvae consume the host until it eventually dies.
Szucs and her team chose two parasitoid wasp species commonly found throughout North America. Researchers initially saw that attack rates in the wild were quite low, and the ability of native species to rapidly adapt to a new food source was unknown. In the lab, the parasitoids were exposed to SWD and forced to prey on them.
Within three generations of selection from a small number of parasitoids — 30 wasps or fewer — successful parasitism improved by 259% for one species and 88% for the other.
“Obviously this is an artificial scenario because we only gave them one option, and in the wild they only attack something if they know to do it,” Szucs said. “But this was a novel way to show that there is some potential to raise native parasitoids and influence their fitness to attack SWD.”
Besides improving native species, the other biological control option is to introduce natural predators. That’s what an MSU team including Isaacs has done with the samba wasp, which is native to Asia. After years of testing and applying for permits, the USDA Animal Plant Health Inspection Service and Michigan Department of Agriculture and Rural Development (MDARD) approved the release of the samba wasp in SWD-threatened locations.
The samba wasp detects already-infested fruit and targets the smallest stages of SWD larvae. Laying its eggs inside its host, the growing samba wasp feeds and ultimately kills the larvae, emerging as a wasp in roughly a month.
The team will continue to evaluate the wasps’ success in the coming growing season, as well as assessing the ability to survive Michigan winters.
“Hopefully they’re able to survive the winter and the populations are robust enough to be successful next year,” Isaacs said. “We don’t expect results right away, but this is a long-term project for us to determine if this can help reduce the need for insecticides and other management strategies moving forward.”
‘Perfect conditions for SWD’
The northwest portion of Michigan’s Lower Peninsula is world renowned for its cherry production. Growers in the Great Lakes State are responsible for 70% of the U.S. supply of tart cherries, about 80% of which are grown in the northwest Lower Peninsula. But the industry is under siege from a variety of sources, from invasive pests and climate change to competition abroad.
SWD, however, has hit the industry particularly hard. Nikki Rothwell, the coordinator of the NWMHRC and fruit specialist with MSU Extension, said this challenge affects every Michigan cherry grower.
Nikki Rothwell, coordinator of the Northwest Michigan Horticulture Research Center.
“If an orchard starts with 100 flies in mid-June, and each female can lay 300 eggs each week, even the best growers with the best programs have a hard time controlling millions of flies,” she said. “Plus, cherries are so attractive that it’s hard to monitor the populations once the fruit get ripe, which makes it hard to make good management decisions based on traditional trapping and integrated pest management strategies we’ve successfully used with other pests.”
One of Rothwell’s initial studies showed that tart cherries create the optimal conditions for SWD. While the flies leave most cropping systems during the day to avoid the hot sun, tart cherry canopies provide a cool layer of protection for them to mate and infest fruit. She found that simply pruning the trees and keeping grass clipped helps immensely.
“We did a pruning study in which we removed different numbers of branches and found that if you remove six to 10 branches in a tart cherry canopy, you can reduce SWD infestation by 40% even without insecticides,” Rothwell said. “We also showed that mowing grass short between tree rows reduced infestation.”
Recent research includes modeling SWD in cherries. Rothwell hypothesized that flies seem to be in the orchard at all times during the summer and begin to lay eggs suddenly. She believed flies were present and waiting for the right time to infest ripening fruit.
To better understand this timing, Rothwell and her team have monitored tart cherries as they ripen over the course of the growing season and brought fruit back to the lab. There, they look at when flies begin infestation. Using this information, the team is producing a model for growers that will more precisely indicate ideal timing for pesticides and other management techniques.
“We’re refining the model now, but we’re hoping to have something soon that growers can use,” Rothwell said. “The industry really depends on MSU to help work through this problem.”
Rothwell’s work has been supported by the Michigan Cherry Committee, MDARD, Project GREEEN and the Foundation for Food and Agriculture Research. — By Cameron Rudolph, Michigan State University
Thirteen UC Davis scientists or former affiliates are among authors from eight countries who contributed to research articles for theJournal of Economic Entomology’sSpecial Collection: Research Advances in Spotted-WingDrosophila suzukii Management.
The recently published Special Collection showcases 14 articles.
Native to Asia, the agricultural pest is a worldwide threat to the berry production industry, which includes raspberries, blackberries, blueberries, strawberries, and cherries. The tiny insect, about 1/12 to 1/8 inch long, invaded the continental United States in 2008.
“All of the papers were by invitation of the co-editors of the special collection—Jana Lee,Cesar Rodrigue-Saona, and me,” said journal editor-in-chiefFrank Zalom, a UC Davis distinguished professor emeritus and recall professor in the Department of Entomology and Nematology. Zalom’s research includes the spotted-wing drosophila.
Lee, formerly with the UC Davis laboratory of the late chemical ecologist Steve Seybold, is a research entomologist with the Horticultural Crops Research Unit, U. S. Department of Agriculture, Agricultural Research Service, Corvallis. Rodriguez-Saona, who received his doctorate from UC Riverside, is an Extension entomologist with the Department of Entomology, Rutgers University, the State University of New Jersey.
In addition to Zalom and Lee, the UC Davis-linked authors include Joanna Chiu and Antoine Abrieux (Joanna Chiu lab); Zain Syed and Kevin Cloonan (Walter Leal lab); Gregory Loeb (Rick Karban lab); and Kelly Hamby, Hannah Burrack, Fatemeh Ganjisaffar, Brian Gress, Nicole Nicola and Mark Demkovich (Zalom lab).
Overall, the Special Collection includes authors from Austria, Brazil, Canada, Italy, Spain, Sweden, United Kingdom, and the United States that represent perspectives from universities, federal and state laboratories, growers, and pest product companies, according to the editors.
One paper, Spatio-temporal Variation of Spinosad Susceptibility in Drosophila suzukii (Diptera: Drosophilidae), a Three-year Study in California’s Monterey Bay Region, is from the Zalom lab and includes co-author, molecular geneticist and physiologist Joanna Chiu, professor and vice chair of the Department of Entomology and Nematology.
The work of molecular geneticist and physiologist Joanna Chiu, professor and vice chair of the UC Davis Department of Entomology and Nematology, is included in the Journal of Economic Entomology’s special collection targeting research on the spotted-wing drosophila. (Photo by Kathy Keatley Garvey)
UC Davis Department of Entomology and Nematology communication specialist Kathy Keatley Garvey provided the cover photo of the spotted-wing drosophila feeding on a raspberry.
Since 2008, “D. suzukii has become a key economical pest of raspberries, blackberries, blueberries, strawberries, and cherries in the United States and worldwide,” the editors wrote in theirintroductory remarks. “Not surprisingly, the number of publications has proliferated from 29 publications as of 2010 to 978 additional publications between 2011 and 2021 from a Web of Science search for ‘Drosophila suzukii.’ While many publications are available, this special collection will highlight advances in D. suzukii pest management since its U.S. invasion. We solicited papers by open call and received 66 abstracts, and selected 14 papers covering: 1) review, 2) monitoring and risk, 3) behavioral control, 4) biological control, 5) cultural control, and 6) chemical control.”
The collection is meant to serve “as a key reference point for entomologists across many institutions (e.g., academia, government, and industry) on important advances in D. suzukii pest management,” according to theEntomological Society of America. “The articles in this collection will also provide scientists information on potential research gaps that will help guide future research directions on this important pest. The goal is to preserve and catalog articles on various aspects of D. suzukii pest management, i.e., monitoring, cultural control, chemical control, behavioral control, and biological control, that will be shared among entomologists.”
Scientists from the Agricultural Research Service (ARS) are working to understand how something can be equally effective as both a government-approved food additive and as a pesticide.
Methyl benzoate is a naturally occurring compound produced by plants. The U.S. Food and Drug Administration long ago approved methyl benzoate for human use; its fruity and floral aroma makes it a staple in perfumes and cosmetics and as a food additive. Nature employs it to attract pollinators.
From left, research chemist Aijun Zhang, postdoctoral Nick Larson, and intern Lauryn Brooks demonstrated research into methyl benzoate uses as a pesticide in an ARS poster day demonstration.
Zhang’s research has focused on methyl benzoate’s utility as a pesticide for human protection and crop protection. So far, Zhang has documented that the compound will kill or repel many insects in various stages of development, including mosquitoes, bed bugs, fire ants, ticks, flies, moths, and the brown marmorated stink bug. Perhaps most important, however, is its ability to repel and kill the spotted wing drosophila fly (SWD). “SWD is the most significant invasive insect pest of soft-skinned fruit crops in the USA,” Zhang said.
Since SWD was first detected in California a little over a decade ago, the fly has become a key pest in blueberries, blackberries, raspberries, strawberries, and cherries. These crops have a combined annual value of over $5.8 billion, and farmers lose about $718 million annually to SWD damage.
Farmers fight SWD with synthetic insecticides, but at prices up to $1,200 per acre, that method is expensive. It is costly in other ways, too, Zhang said; the synthetic insecticide is harmful to the environment, contributes to pesticide resistance, and may be harmful to humans.
Because methyl benzoate is an environmentally friendly, bio-based compound, Zhang thinks it has great potential to be used by people for human protection as an alternative to synthetic pesticides. It also costs much less than synthetic pesticide treatments.
According to Zhang, methyl benzoate shares the same “chemical skeleton” as DEET, the gold standard in arthropod repellency, a detail that is leading future research efforts.
“Understanding the structure-activity relationship will allow researchers to modify the chemical structure of the methyl benzoate molecule to develop pesticides that are more efficient at controlling arthropod pests,” he said. — By Scott Elliott, USDA-ARS Office of Communications.
Scientists from the Agricultural Research Service (ARS) are working to understand how something can be equally effective as both a government-approved food additive and as a pesticide.
Methyl benzoate is a naturally occurring compound produced by plants. The U.S. Food and Drug Administration long ago approved methyl benzoate for human use; its fruity and floral aroma makes it a staple in perfumes and cosmetics and as a food additive. Nature employs it to attract pollinators.
From left, research chemist Aijun Zhang, postdoctoral Nick Larson, and intern Lauryn Brooks demonstrated research into methyl benzoate uses as a pesticide in an ARS poster day demonstration.
Zhang’s research has focused on methyl benzoate’s utility as a pesticide for human protection and crop protection. So far, Zhang has documented that the compound will kill or repel many insects in various stages of development, including mosquitoes, bed bugs, fire ants, ticks, flies, moths, and the brown marmorated stink bug. Perhaps most important, however, is its ability to repel and kill the spotted wing drosophila fly (SWD). “SWD is the most significant invasive insect pest of soft-skinned fruit crops in the USA,” Zhang said.
Since SWD was first detected in California a little over a decade ago, the fly has become a key pest in blueberries, blackberries, raspberries, strawberries, and cherries. These crops have a combined annual value of over $5.8 billion, and farmers lose about $718 million annually to SWD damage.
Farmers fight SWD with synthetic insecticides, but at prices up to $1,200 per acre, that method is expensive. It is costly in other ways, too, Zhang said; the synthetic insecticide is harmful to the environment, contributes to pesticide resistance, and may be harmful to humans.
Because methyl benzoate is an environmentally friendly, bio-based compound, Zhang thinks it has great potential to be used by people for human protection as an alternative to synthetic pesticides. It also costs much less than synthetic pesticide treatments.
According to Zhang, methyl benzoate shares the same “chemical skeleton” as DEET, the gold standard in arthropod repellency, a detail that is leading future research efforts.
“Understanding the structure-activity relationship will allow researchers to modify the chemical structure of the methyl benzoate molecule to develop pesticides that are more efficient at controlling arthropod pests,” he said. — By Scott Elliott, USDA-ARS Office of Communications.
If the birds don’t get to your cherries, Spotted Wing Drosophila will, injecting their larvae right into the fruit. Watch this brief video with UC Cooperative Extension Specialist Kent Daane as he shares how to manage this pest that has managed to spread all over the United States. Read more about orchard pest and disease management in California Fresh Fruit Magazine.
