Mitchell Scholar Crosby Researches Ways to Curb the ‘Scourge’ of the Browntail Moth

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As CBS News has reported, “The browntail moth is a scourge in America’s most forested state, where it defoliates trees and causes a rash in humans that resembles poison ivy.”

Fortunately, a Mitchell Scholar is on the front lines of finding ways to manage the white-winged menace.

Sadia Crosby sets an experimental browntail moth trap containing a pheromone-based lure on Sears Island in Searsport, Maine. (Photo by Dr. Angela Mech.)

Sadia Crosby, the 2013 Scholar from Morse High School and current master’s-in-entomology candidate at the University of Maine, is now studying various types of traps and pheromone-based lures to determine the most effective combination for capturing the moth. As the purity or potency of the lure increases, so does its cost of production, which is why part of Crosby’s research has involved determining the optimal level required to attract the moth.

“No surprise — they prefer the more expensive, higher-purity lure,” she said with a laugh. “I wouldn’t have expected anything less from this creature.”

Joking aside, Crosby said there’s more at stake with the research than curbing the spread of the barbed, toxic hairs that are shed and become airborne during the moth’s caterpillar stage.

“It was first thought that they were attracted to hardwoods, apple, and nut trees,” said Crosby, who became a licensed pesticide applicator with a Phippsburg-based tree service after earning a degree in environmental science at Roger Williams University. “But we have seen evidence that browntail moths can feed on Douglas fir, and we know that conifers aren’t as resilient as hardwoods when it comes to defoliation. If conifers lose needles, that’s highly problematic for the health of the tree.”

In addition to managing the browntail moth through lures and traps, Crosby has been involved with research into the efficacy of bacterium-based biopesticides. In multiple lab trials, moth larvae were fed treated leaves and monitored to measure potential effects. The analysis of data from the study is ongoing.

Samples of the white-winged moth captured in a pheromone-baited experimental trap set by Crosby as part of her master’s-degree research.

Crosby said the browntail moth is not a new pest to Maine. Outbreaks were documented in the early 1900s as well as the ’50s, ’60s, and early ’90s. But none of those surges rivals the intensity of the current outbreak, which is in its seventh year.

“We’re still trying to figure out its role in the environment,” she said. “I don’t think we’re ever going to eliminate the browntail moth. Instead, I think we may develop stronger monitoring and management programs to keep their populations below the outbreak levels we are currently facing.”

With one semester remaining in her master’s program, Crosby said she has her sights set on returning to the public or private sector rather than earning a doctoral degree in entomology.

“It’s hard right now, not to be helping the public directly with the browntail moth outbreak,” she said. “Offering people solutions right on the spot is more my calling. I want to work with communities and municipalities to figure out solutions and strategies. That’s where I see myself heading after graduate school.”

For now, there’s her own research to complete as well as her thesis advisor’s research to support before her degree program and research assistantship conclude in May 2023. Through it all, Crosby has kept the pest in perspective.

“The browntail moth has been my arch nemesis, and it’s also brought me a lot of opportunity,” she said. “When I meet people and explain the focus of my research, they either shudder in fear or tell me they’re grateful that somebody is doing something about it. Entomology is a great field, and there’s still so much to learn about the browntail moth.”

Crosby conducts a spray trial on some of the orchard trees in spring 2022 using different bacteria-based biopesticides at Highmoor Farm in Monmouth, Maine. Crosby says additional support from the Mitchell Institute, in the form of two fellowships, made two research experiences possible:  a 2016 trip to Costa Rica to learn about sustainability studies in the tropics and the initial phase of studies conducted at browntail moth “hot spot” sites statewide in 2021. (Photo by Devin Rowe.)