It did recently at the University of California, Davis.
Take the case of the walnut twig beetle, Pityophthorus juglandis, which in association with the canker-producing fungus, Geosmithia morbida, causes thousand cankers disease, which kills walnut trees, especially wreaking havoc on black walnuts.
The late Steve Seybold (1959-2019), a UC Davis-affiliated entomologist and global authority on the insect, fungus and disease, accidentally discovered an insect repellent when he was setting pheromone traps in Davis nearly two decades ago to assess the beetle's seasonal flight patterns. When he ran out of the adhesive, Stickem Special, he substituted Tree Tanglefoot.
Seybold, who specialized in the chemical ecology of forest insects, observed that every single beetle avoided Tree Tanglefoot, which contains the semiochemical limonene. Was Tree Tanglefoot a potential repellent? Maybe a very potent repellent?
Seybold, who died Nov. 15, 2019, never got to continue the research, but his mentee, Jackson Audley did and is the lead author of newly published research, “Trapping Failure Leads to Discovery of Potent Semiochemical Repellent for the Walnut Twig Beetle,“ in the Journal of Economic Entomology. Seybold is listed as a co-author.
At the time of his discovery, Seybold was serving as part-time lecturer and researcher with the UC Davis Department of Entomology and Nematology and a full-time researcher with the Pacific Southwest Research Station, USDA Forest Service, Davis.
While at UC Davis, Audley investigated behavioral chemicals that repel the walnut twig beetle from landing on English walnut trees. Audley is now a postdoctoral fellow funded by the Oak Ridge Laboratories and based at the USDA's Davis headquarters.
The repellent effect of limonene may be valuable in the development of a semiochemical-based tool for management of P. juglandis and thousand cankers disease, Audley points out.
“The trapping failure with the new adhesive occurred from May to September 2011,” Audley said. “The chemical analyses and all of the subsequent testing of limonene occurred following that year. Most of the subsequent repellent trapping studies were conducted at the Wolfskill Experimental Orchards in Winters.”
“Limonene having a repellent effect on the walnut twig beetle was not particularly surprising,” Audley pointed out, “and repellency has been shown in other scolytines. It was more the manner in which this repellent semiochemical was found that was a little bit surprising. Limonene happened to be an additive in the formula for a secondary brand of adhesive used for sticky card traps that the lab used early on in walnut twig beetle trapping. The next step was to test limonene plus a few other repellent compounds in combinations (see Audley et al. 2020 https://doi.org/10.1007/s10886-020-01228-9) and then finally to test the most successful combination at reducing trap catches on individual trees to see if the combination conifers protection from colonization of the whole tree.” The final paper (testing the combination on walnut trees in an orchard) was submitted to the Journal of Economic Entomology and “is under current review.”
Entomology Today, a publication of the Entomological Society of America, picked up the story and headlined it: "Scientists Stumble Upon Promising Repellent for Beetle Pest." Audley told science writer Paige Embry, that "Oftentimes, the game for finding repellents, especially within bark beetle systems, is almost like a fishing expedition—of throwing a whole bunch out there and then slowly whittling down.”
Wrote Embry: “The next step is to figure out whether, and how, limonene can be used to protect individual trees and orchards—presumably something short of covering trees from top to bottom in Tanglefoot.”
The abstract (the work of Audley and scientists Paul Dallara, Lori Nelson, Shakeeb Hamud, Richard Bostock and the late Steve Seybold):
"The walnut twig beetle, Pityophthorus juglandis Blackman, and its associated fungal pathogen that causes thousand cankers disease, currently threaten the viability of walnut trees across much of North America. During a 2011 assessment of seasonal flight patterns of P. juglandis with yellow sticky traps baited with the male-produced aggregation pheromone component, 3-methyl-2-buten-1-ol, dramatically reduced catches were recorded when Tree Tanglefoot adhesive was used to coat the traps. In summer 2011, two trap adhesives were tested for potential repellency against P. juglandis in a field trapping bioassay. SuperQ extracts of volatiles from the most repellent adhesive were analyzed by gas chromatography–mass spectrometry, and limonene and α-pinene were identified as predominant components. In field-based, trapping experiments both enantiomers of limonene at a release rate of ~700 mg/d conferred 91–99% reduction in trap catches of P. juglandis to pheromone-baited traps. (+)- and (‒)-α-Pinene reduced trap catch by 40 and 53%, respectively, at the highest release rate tested. While a combination of R-(+)-limonene and (+)-α-pinene resulted in a 97% reduction in the number of P. juglandis caught, the combination did not consistently result in greater flight trap catch reduction than individual limonene enantiomers. The repellent effect of limonene may be valuable in the development of a semiochemical-based tool for management of P. juglandis and thousand cankers disease."
Walnut Twig Beetle (UC Statewide Integrated Pest Management)
- "A Study of Landing Behaviour by the Walnut Twig Beetle, Pityophthorus juglandis, Among Host and Nonhost Hardwood Trees in a Northern California Riparian Forest" (https://doi.org/10.1111/afe.12385).
- "Walnut Twig Beetle Landing Rates Differ Between Host and Nonhost Hardwood Trees under the Influence of Aggregation Pheromone in a Northern California Riparian Forest" (https://doi.org/10.1111/afe.12410)
The walnut twig beetle, in association with the fungus, Geosmithia morbida, causes the insect-pathogen complex known as "thousand cankers disease," which wreaks havoc on walnut trees. The insect, measuring about 1.5 millimeters long, is smaller than a grain of rice.
"The first study is one of few bark beetle host selection studies conducted without the use of semiochemical lures," Audley said. "Together, both studies provide strong evidence for directed flight host searching and in-flight, host discrimination behaviors by Pityophthorus juglandis. These papers highlight sources of and provide an ecological context for potential non-host, volatile compounds that may be of use in semiochemical repellents to protect walnut trees from attack by P. juglandis."
The beetle? The walnut twig beetle, Pityophthorus juglandis.
In association with the fungus, Geosmithia morbida,it causes the insect-pathogen complex known as "thousand cankers disease," which wreaks havoc on walnut trees.
Audley will share his research at his exit seminar, "Semiochemical Interruption of Host Selection Behavior of the Invasive Walnut Twig Beetle, Pityophthorus juglandis," set for 4:10 p.m., Wednesday, Dec. 4 in 122 Briggs Hall, UC Davis campus. It's open to all interested persons.
Jackson, who joined the UC Davis doctoral program in September 2015, investigates behavioral chemicals that repel the walnut twig beetle from landing on English walnut trees. He conducts his research in a commercial orchard near Winters.
Audley says in his abstract: "The walnut twig beetle (WTB) is an invasive bark beetle pest of walnut trees in California and throughout much of its recently expanded range across the North American continent. Feeding by the beetle and canker development by the associated fungal pathogen, Geosmithia morbida, constitute the progressive and often fatal, thousand cankers disease. Management efforts to protect walnut trees are currently lacking. Here I present work related to understanding and manipulating WTB chemical ecology. First, we investigate the beetle's host-searching behavior in the context of a dense, native riparian forest habitat. The goal was to establish WTB's inflight sensitivity to host and non-host cues. Next, I present the results of flight-intercept behavioral assays of four potentially repellent volatile compounds: limonene, chalcogran, concophthorin and verbenone, first individually and then in compounds in reducing trap captures in the context of WTB aggregation phermone.
"Finally, we tested the most effective combination on whole walnut trees in a commercial, English walnut orchard. We compared beetle landing rates on treated and untreated trees as a correlate for WTB attacks. I report that we effectively reduced the number of WTB landing on treated trees; however, the repellent effect was spatially limited. Thus, further testing is required prior to recommending a management schedule. This work did provide proof of concept of semiochemical interruption in a hardwood attacking bark beetle system."
Audley, on a path to receive his doctorate in entomology this month, studied with Steve Seybold, who tragically died Nov. 15 of heart disease. Seybold was a lecturer and faculty affiliate with the UC Davis Department of Entomology and Nematology and a forest entomologist and chemical ecologist with the Pacific Southwest Research Station, USDA Forest Service, Davis.
Louie Yang, associate professor, UC Davis Department of Entomology and Nematology and Professor Richard “Rick” Bostock of the UC Davis Department of Plant Pathology serve as mentors. The Bostock lab is heavily involved with the chemistry side of Audley's repellent research.
A native of Washington, D.C., Jackson spent most of his childhood in Atlanta, Ga. He was first introduced to forest entomology while studying at the University of Georgia, Athens, where he received his bachelor of science in wildlife biology and natural resource recreation and tourism in 2009. He went on to receive his master's degree in forestry in 2015 from the University of Tennessee, Knoxville, where he focused his thesis on managing the walnut twig beetle in cut black walnut logs, live edged boards, and nursery stock.
He recently received the 2019 Western Forest Insect Work Conference Memorial Scholarship Award for his research on the chemical ecology of the walnut twig beetle.
His career plans? “I plan to devote my career to conducting chemical ecology-based research of bark and wood boring beetles that threaten trees in forest landscapes in the western U.S.,” Audley said. “In this capacity, I plan to continue adding to the scientific understanding of bark beetle ecology and management.”
Audley aims to engage with the scientific community and public alike in the arena of forest health issues and sound forest management practices. “Our western forests are in dire need of sound forest management to return them to a healthier state, and I plan to conduct and disseminate research to help achieve that goal.”
Community ecologist Rachel Vannette, assistant professor, is coordinating the weekly seminars. (See list of seminars)
Steve passed away Friday, Nov. 15 at a Sacramento hospital of a heart condition. Born in 1959 in Madison, Wisconsin, he was 60 years old. He was one of the pioneering scientists researching the newly discovered thousand cankers disease (TCD), caused by the walnut twig beetle, Pityophthorus juglandis, in association with the canker-producing fungus, Geosmithia morbida. He was a worldwide authority on the insect, fungus and disease. (See obituary in Davis Enterprise)
In his memory, he was honored with a moment of silence this week at the Entomological Society of America meeting in St. Louis, Mo.
The tributes are pouring in:
Nematologist Steve Nadler, professor and chair of the UC Davis Department of Entomology and Nematology: "Steve was an excellent chemical ecologist whose research on insect pests of trees proved to be of great importance to landscapes throughout North America.”
Chemical ecologist Walter Leal, UC Davis Department of Molecular and Cellular Biology and past chair of the UC Davis Department of Entomology (now the Department of Entomology and Nematology). "Chemical ecology lost a champion, forestry entomology lost an ally, and we will miss a friend and colleague. Steve served the International Society of Chemical Ecology as Councilor, the Journal of Chemical Ecology as Associate Editor, and mentored many undergraduate and graduate students and postdoctoral scholars. He elucidated biochemical mechanisms related to bark beetle pheromones, leaving behind a legacy of papers and review articles, some of which have already been cited almost one thousand times. I copied from him the style of praising colleagues when citing their good work by adding the advert 'elegantly' like in the following sentence. Steve Seybold elegantly demonstrated how bark beetles make their pheromones."
Doctoral student Jackson Audley of the Seybold lab: "Steve Seybold was a brilliant scientist and an integral component of the forest entomology community, especially here in the western USA. I admired the amount of time he spent out in the field. I have often heard it said that once a field biologist obtains a Ph.D., that they often become something of an 'armchair biologist', not Steve. I have never seen him happier than when he was out on long field excursions, hunting down various trees and tree pests. I hope to emulate that characteristic in my own career. Although my time working with Steve now feels cut abruptly and unfairly short, he imparted a great deal of wisdom upon me in that time. I am incredibly grateful to have had Steve as a mentor and a friend. He contributed a great deal to making me into the scientist I am today. He will be sorely missed."
Seybold lab alumnus Andrew Graves (now a zone leader entomologist with the Forest Service, Forest Health Protection, New Mexico Zone): "We are all shocked and saddened. Steve and I worked together for nearly 20 years. A faithful mentor, constant teacher, an incessant researcher to whom the time of day or length of time were meaningless, a good friend who contributed much to our world. A too early passing and a great loss for us all. He was a good man and will be missed by many. If I had to guess, he would've been disappointed he didn't finish that last manuscript."
Seybold lab alumnus Stacy Hishinuma, who went on to accept a position in the Pacific Southwest Region, San Bernardino: "Steve was a pivotal person in my life. I worked with him for more than 10 years and during that time he pushed me to have the highest scientific standards and taught me all I know about research. He was an involved mentor and cared deeply about the success of his students. His love was expressed through the red marks on our manuscripts, the time he spent helping us with presentations, and the pop quizzes on insect identification. When I started graduate school, people advised me to be the first person in and the last person to leave. This was impossible in the Seybold lab since Steve regularly started working before dawn. It was somehow always startling when I would email Steve at 4:00a, before heading to sleep, and he would immediately respond. Steve's work ethic was unprecedented. It was inspiring to see his passion for research. His love for science was only rivaled by his love for his daughters. I'll always miss the conversations we had driving to field sites, eating at his go-to restaurants, and geeking out about bark beetles. Thank you for everything Steve. I hope I can help carry on your legacy through my own work as a forest entomologist."
We knew him as an incredible scientist with an immense curiosity, an outstanding teacher, and a kind and caring friend. A few of the last news stories we wrote about him:
- A Sign of the Times: Why This Black Walnut Tree Is Dying
- Meet the Extreme Insects at the Bohart Museum of Entomology Open House
- Walnut Twig Beetle and Fungus Has Caused 'Profound Damage to Black Walnut Trees
Steve is survived by his widow, Julie Tillman, and daughters Natalie, 11, and Emily, 17. "Steve loved his work and his daughters with his whole self and heart," Julie said. "He will be sorely missed by his family and friends, his lab family and his huge network of professional colleagues."
A visitation will be held from 5 to 7 p.m. Friday, Nov. 22, at Smith Funeral Home in Davis. A service will be held on Saturday, Nov. 23, at Saint James Church in Davis at 10 a.m. with interment at a later date near his father at Forest Hill Cemetery in Madison. Memorials in his name may be made to the American Heart Association, National Parks Conservation Association or the Entomology and Nematology Student Support fund at UC Davis.
It's about the size of a grain of rice but it's a killer.
That's the walnut twig beetle, Pityophthorus juglandis, which in association with a newly described fungus, Geosmithia morbida, causes thousand cankers disease, wreaking havoc on native black walnut trees.
Enter doctoral student Jackson Audley of the Steve Seybold lab, UC Department of Entomology and Nematology. He will present a seminar on "Protecting Trees from Bark Beetle Attacks Utilizing Semiochemical Repellents: A Case Study with the Walnut Twig Beetle” at a seminar from 4 to 5 p.m., today (Wednesday, Oct. 25) in Room 3001 of the Plant and Environmental Science Building.
The seminar is part of the UC Davis Forest Biology Research Center Seminar Series and his presentation is a preview of his thesis project.
"In this talk I will discuss the theoretical construct of semiochemical repellents for protecting trees from attack by bark beetles and demonstrate the process of developing a repellent tool with my work on the walnut twig beetle, Pityophthorus juglandis, the vector of thousand cankers disease in walnuts," Audley says in his abstract. "Bark beetles can constitute a significant threat to tree health and are a significant disturbance agent in forest ecosystems. Semiochemicals have been successfully utilized to protect individual to stands of susceptible trees from various bark beetle pests. Most of this work has been conducted in coniferophagous bark beetle systems. My work here at UC Davis has been focused on bringing those same techniques into studying an invasive, hardwood-attacking bark beetle system."
Audley received his bachelor's degree in wildlife biology and natural resource recreation and tourism in 2009 from the University of Georgia, and his master's degree in forestry in 2015 from the University of Tennessee. As a master's student, he did research on the walnut twig beetle, including treatment tests.
The walnut twig beetle is believed to be native to Arizona, California, New Mexico and Mexico. In 2006, plant pathologist Ned Tisserat and entomologist Whitney Cranshaw of Colorado State University identified the pathogen in declining black walnut trees in central Colorado. The disease has now spread throughout much of the United States.
"Often the first symptoms of thousand cankers disease (TCD) are flagging and yellowing leaves and branch dieback," says Seybold, one of the pioneering TCD researchers. He is a chemical ecologist with the USDA Forest Service, Pacific Southwest Research Station, Davis, and a lecturer/researcher with the UC Davis Department of Entomology and Nematology. "Affected branches show sap staining and pinhole-sized beetle holes. Beneath the surface are dark stains caused by the fungus."
"The fungus enters the tree through the feeding or reproductive activities of the beetle, and colonizes and kills the phloem and cambium of the branches and main stem," according to the UC Integrated Statewide Integrated Pest Management Program website, content that's the work of Steve Seybold and entomologist Mary Lou Flint, then associate director of of Urban and Community IPM, and now UC Extension entomologist emerita. The disease gets its name from the large number of dark cankers that rapidly develop on affected branches.
The UC Davis Forest Biology Research Seminars, which began Oct. 11, are held Wednesdays at 4 p.m. in Room 3001 of the Plant and Environmental Science Building.
The remaining schedule includes:
Nov. 1 – Alison Scott, postdoctoral student, UC Davis Department of Plant Sciences, “The Polyploid Origin and Evolutionary History of California Redwoods”
Nov. 15 – Brian Smithers, Ph.D student, Ecology Graduate Group, "Mechanisms of Range Shifts in Great Basin Sub‐Alpine Bristlecone Pine Forests."
Nov. 29 – Sarah Bisbing, assistant professor, Forest Ecosystem Science, Department of Natural Resources and Environmental Science, University of Nevada, Reno, "Looking Backward to See Forward: Causes and Consequences of Altered Disturbance and Climate on Western Conifer Forests.”
Dec. 6 ‐ Ryan Tompkins, Forest Silviculturist, U.S. Forest Service/Plumas National Forest, “Sierra Nevada Silviculture in the New World Order: Challenges, Uncertainties, and Opportunities”
For more information, contact David Neale at firstname.lastname@example.org.