Preventing Mushy Blueberries by Managing Spotted Wing Drosophila
UNH study investigates integrated pest management methods for invasive SWD
Tuesday, July 25, 2023
  • A cluster of blueberries taken at the blueberry orchard at the Woodman Horticultural Research Farm.

    UNH researchers are studying cultural controls for the management of spotted wing drosophila (SWD), an invasive fruit fly that has decimated berry and other fruit crops around the country. Photo credit: Catherine Coverdale

  • An image of spotted-winged drosophila

    An image of spotted wing drosophila (SWD) (Drosophila suzukii). Photo credit: Ìęby

  • On the left, an image of the spotted wing drosophila (SWD). On the right, an image of an SWD larva emerging from a blueberry.

    Left, a spotted wing drosophila (SWD). Photo credit: . Right, an SWD larva emerging from a blueberry. Photo credit: Catherine Coverdale

  • Researcher and UNH graduate student Catherine Coverdell ’22 checks for signs of the spotted wing drosophila.

    Researcher and UNH graduate student Catherine Coverdell ’22 checks for signs of the spotted wing drosophila (Drosophila suzukii) at the blueberry orchard at .

  • Two different ground covers shown beneath the blueberry plants.

    UNH researchers are studying the use of weed matts (in white) beneath blueberry plants to reduce the proliferation of spotted wing drosophila in orchards.

  • A photo of the blueberry orchard, located at the Woodman Horticultural Research Farm at the Âé¶čapp in Durham.

    The blueberry orchard at the Woodman Horticultural Research Farm at the Âé¶čapp in Durham.

Key Takeaways & Goals:

Spotted wing drosophila (SWD) has a rapid reproductive cycle, with the ability to breed an entire generation every 10 days during the summer. Traditional approaches to managing SWD have involved aggressive spray programs.

UNH researchers are studying cultural integrated pest management (IPM) strategiesÌęto prevent SWD populations from establishing and growing. These strategies include using organic-approved sanitizer sprays that remove yeast food odors from the fruit and leaves andÌęinvestigating the use of weed matting to hinder the SWD reproduction cycle.

The use of a parasitic wasp called Ganaspis brasiliensis is being researched as a potential biological control agent for SWD, however, the distribution of this wasp for commercial use is not yet available.

The timing and severity of SWD outbreaks can vary due to changes in long-term climate patterns and weather variability. Warm, wet conditions can lead to a population explosion of SWD, causing significant infestations in fruit crops.

COLSA Student Researchers: Examining Real-World Issues, Finding Innovative Solutions

Catherine Doheny Coverdale earned her —with a focus on food access and community health—before pursuing her at COLSA. She’s worked in the lab of Anna Wallingford since 2020.

"I was influenced to pursue agricultural research after working on a farm that implemented integrated pest management (IPM) practices," said Coverdale. "It was there that I gleaned a deep understanding of the hard work that goes into providing a community with fresh flowers and produce, as well as the importance of sustainable farming practices.”

She added, "IPM research is vital for local food systems. This method of pest management ensures that farmers can achieve profitable yields while minimizing environmental impact. And developing research questions that align with the needs of local farmers fosters a more collaborative and resilient approach to achieving agricultural sustainability."

A headshot of Catherine Coverdale, a graduate student at the UNH College of Life Sciences & Agriculture

Catherine Coverdale

A New England summer isn’t complete without a slice of juicy blueberry pie and eating a few crisp berries as an afternoon treat. But the (Drosophila suzukii), or SWD, a pesky fruit fly native to Southeast Asia that was first identified in the U.S. a little more than a decade ago is wreaking havoc on fruit crops producers—from commercial farms to the backyard garden. scientist is seeking new approaches to manage a rapidly growing challenge that already causes annually to the U.S. and is a yearly threat to more than .

“SWD impacts everyone who grows fruit and can be found in every region of the state,” said Wallingford, a research assistant professor in the . “When it first came on the scene, many fruit growers in the Northeast were left with two choices: adopt aggressive spray programs or bulldoze over their blueberries and fall-bearing raspberries and plant something else.”

Unlike native fruit flies that lay their eggs in rotting fruit and other organic matter, SWD prefer ripe or ripening fruit that’s still on the bush waiting to be picked. Once the eggs hatch, the larvae eat and grow in the fruit, which becomes mushy and falls to the ground. Larvae enter the soil, pupate (transform to their adult stage) and emerge to attack the crop again. During the summer, SWD can breed an entire generation every 10 days, resulting in exponential population growth.

“Over the past 10 years, many folks have learned to live with this pest and adopted several IPM [integrated pest management] strategies to offset many of those sprays,” she added. “The cultural and biocontrol strategies that we’re investigating will contribute to reducing that pressure.”

Investigating Weed Matting & Sanitizer Spray

Cultural strategies or controls are used to prevent pest populations from establishing and growing. , a graduate student in the Agricultural Sciences program and a member of , is currently examining the use of an organic-approved sanitizer spray that removes yeast food odors, which attracts the flies, from the fruit and leaves. She is also investigating whether using fabric covers—primarily intended to prevent weeds in orchards—could also help slow or stop the reproduction cycle of SWDs.

“Blueberries used to be a really low-intensity crop, so growers didn’t have to use a lot of management practices until this fly arrived,” said Coverdale. “Now they’re having to do regular spraying and sanitizing of the fruit, making growing them and other berries much more time intensive.”

By using weed mats below blueberry bushes, infested and fallen fruit lands on the mats and prevents the larvae from being able to reach the soil. This impedes the insect larvae from burrowing into approximately the top 2 centimeters of soil, where they prefer to pupate in a protected, humid environment.

“Summer 2023’s warm wet conditions have already resulted in a population explosion that’s 3-4 weeks earlier than the previous year—so it’s shaping up to be a doozy of a year for SWD infestations.”Ìę Ìę Ìę~Ìę, research assistant professor, COLSA

“The weed mat both reduces weeds and creates a barrier between the SWD larva and the soil environment,” added Coverdale. “It’s also possible that the mats reduce humidity and increase reflective light and temperatures—none of which the larvae prefer—so we’re investigating the light reflectiveness, humidity and temperature of two different mat types as well.”

Ganaspis Brasiliensis as a Cultural Control

Future research in Wallingford’s lab will focus on using —a small parasitic wasp that lays its eggs in the larvae of SWD, specifically those in blueberries—as a biological control. Wallingford and her team are currently growing this parasitic wasp for distribution and release at New Hampshire farms. ; .

An image of fly traps used to monitor for the presence of spotted wing drosophila at Woodman Horticultural Research Farm at UNH.

An image of Ganaspis brasiliensis laying eggs in spotted wing drosophila larva within a blueberry.

Left: A fly trap used to determine the presence of spotted wing drosophila and the start of management practices at the . Right: A Ganaspis brasiliensis laying eggs in spotted wing drosophila larva within a blueberry. Photo by Dr. Kent Daane, University of California, Berkeley.

“We’re part of a group of researchers investigating whether or not lab grown Ganaspis brasiliensis are reproducing and establishing in SWD populations after we’ve released them in the field,” said Wallingford. “However, we’re just at the research stage of things, so these biological control agents won’t be available for purchase anytime soon.”

, meaning that strawberries and some of the earlier maturing blueberries and raspberries often face lower infestation levels. When humidity and temperatures rise and create ideal for SWD reproduction and growth, populations of the invasive pest can grow rapidly. While these conditions are typically seen in July, changes in long-term climate patterns and weather variability could make the timing and severity of SWD outbreak less predictable.

“The hot, dry conditions of summer 2022 kept SWD populations low,” said Wallingford. “However, summer 2023’s warm wet conditions have already resulted in a —so it’s shaping up to be a doozy of a year for SWD infestations.”

This material is based on work supported by the through joint funding from the (under Hatch award numbers 1022400 and 7004988) and the state of New Hampshire.

On the , you'll find additional information on and .

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