Understanding the intricacies of insect behavior and communication can help understand evolutionary biology among pests and also contribute to developing pest management practices. One of the most promising tools in this field is the use of pheromones, which plays a crucial role in detecting and controlling pest populations.

Ksenia Onufrieva is a research scientist in the Department of Entomology and studies the spongy moth, formerly known as the gypsy moth. She said it is one of the most devastating forest pests in the eastern United States because it feeds on over 300 species of trees and shrubs. Defoliation, or removing the leaves of trees, reduces growth rates and makes the spongy moth vulnerable to other pests, pathogens, and stress. In very young trees, defoliation can even cause mortality, meaning it is important to control pests that feed on these trees and shrubs.

One of the most effective control strategies is to disrupt mating. It involves the application of spongy moth pheromones, which are chemicals emitted for mating communication, over a large area to prevent flying males from finding calling flightless females and mating with them.

“This method is the most environmentally friendly because it is species specific and does not harm any non-target organisms,” said Onufrieva.

The ability to measure pheromone concentrations in the air offers insights into pest behavior, optimizing control strategies and ensuring the effective application of pheromone-based treatments. However, many of the current methods for detecting pheromones are complex, expensive, and limited in portability.

Onufrieva and Gabriel Isaacman-VanWertz teamed up on a College of Agriculture and Life Sciences supported project to develop and deploy samplers for distributed sampling of volatile organic compounds, which are any of thousands of different carbon-containing gases emitted for biological and ecological purposes.

“This can be things like the smell of pine trees or the scents animals and insects use to signal information to each other,” said Isaacman-VanWertz. “The same types of compounds are also emitted through human activities and in some cases can be hazardous air pollutants, so sampling these gases is important for many different reasons.” 

Detecting pheromones in spongy moth populations

Onufrieva coordinates research on the spongy moth, a forest pest that was introduced to the United States in 1869. The main goal of her research is to optimize the mating disruption tactic implemented against the spongy moth by the National Slow the Spread Program (STS) to keep the moths from multiplying. The program is a cooperative effort between the U.S. Department of Agriculture (USDA) Forest Service, USDA Animal and Plant Health Inspection Service, 11 states, and two universities to reduce the rate of spongy moth spread by 60 percent from the historical spread rate. This involves continuous monitoring of the 1,600-mile area adjacent to the main population front in Goshen, Virginia, and by treating low-density colonies that become established just beyond those moth communities.

Onufrieva and Isaacman-VanWertz are leading a team of two faculty from the Department of Entomology, one faculty from the Charles E. Via, Jr. Department of Civil and Environmental Engineering, and three civil and environmental engineering students to develop a system for detecting the spongy moth pheromone, also called disparlure. They created 13 portable, battery-powered, weatherproof volatile organic compound samplers. These samplers are designed to autonomously collect air samples containing pheromones under field conditions. The samplers can run for at least 24 hours on a single charge, making them highly practical for field research. 

Inside of air sampler
The inside of the portable tube samplers. Photo courtesy of Ksenia Onufrieva.

These portable and programmable volatile organic compound samplers are poised to transform air quality monitoring through high precision and use of miniature ozone scrubbers that preserve samples collected. These samplers were proven to be accurate in indoor environments as well as outdoor sources of chemical substances.

“We were able to use these samplers to develop a new approach to map an area and identify hotspots,” said Isaacman-VanWertz. “Since the samplers are portable and cheap to make, we can collect many samples along perpendicular transects on a grid then identify points in the grid that have high concentrations.”

That allows team members to map an area with much higher resolution than the number of samples they have to collect. “Identifying hot spots could mean detecting populations of various organisms, including spongy moths,” said Onufrieva. She added that spongy moth populations occur in patches and sometimes high-density populations are difficult to detect using traps. An air sampler would be helpful to detect isolated populations.

The goal was to measure disparlure in the field and characterize plumes produced by spongy moth females and disparlure-baited traps.

Samplers were placed in plots aerially treated with disparlure and in untreated control plots located in Goshen Wildlife Management Area. Each deployment consisted of four samplers placed in a wire basket and elevated 10 meters above the ground within the canopy. To test and improve the samplers, data also was collected inside labs at Virginia Tech in an office in which a wall of plants was installed and in test areas around the Blacksburg campus, such as the Drillfield and a park near the golf course.

researchers putting samplers in tree canopy
(From left) Alejandra Caceres and Gabriel Isaacman-VanWertz deploy the samplers in the tree canopy. Photo courtesy of Ksenia Onufrieva.

Challenges create opportunities

Despite other successes, the team was unable to detect disparlure in the field samples.

“Disparlure is a very sticky compound that gets lost to sample lines and instruments. One of the successes of these samplers is that the design lets us sample even these sticky, difficult-to-measure chemicals,” said Isaacman-VanWertz. However, pheromone concentrations are incredibly low, as small as a part-per-quadrillion, which makes them difficult to detect. 

The team did measure the disparlure at very low concentrations in the lab, putting an upper limit on the concentration in the field samples that provided successful treatment.

“This was a big success because we showed very low limits of detection for many different compounds and developed a new sampling and mapping approach to find hotspots of concentrations,” said Isaacman-VanWertz.

The inability to detect disparlure in the field does not mark the end of this research journey. It is merely a stepping stone for further refinement and optimization. Adjustments to the air sampling method are planned for 2024 and beyond, with the aim of pumping significantly larger volumes of air through the adsorbent tubes to detect volatille organic compounds at lower concentrations and improve chances of detecting pheromones in the field.

The samplers created for this project proved to be useful in many other areas, including indoor environmental measurements involving plants and preliminary collection of airborne particles containing insect DNA to locate and survey insect populations. In fact, the project’s success led to further development efforts with the USDA collaborating to build 32 additional, higher-flow samplers, 12 of which have already been constructed at Virginia Tech.

The next steps are to use these samplers for more types of volatile organic compounds. Isaacman-VanWertz brought two to Ecuador to measure urban and forest gasses during his studies as part of a Fulbright scholarship. He is using them as part of an Environmental Protection Agency project to measure potential hazardous air pollutants. 

“The results in this study provide guidance for further development of the air sampling technique, but they also lay the foundation for further research to optimize pheromone-based pest management,” said Onufrieva. 

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