Forest health promises to take a turn for the better, thanks to forest entomologists like Jackson Audley, a doctoral student at the University of California, Davis.

Audley just received the 2019 Western Forest Insect Work Conference (WFIWC) Memorial Scholarship Award for his research on the chemical ecology of an invasive bark beetle, the walnut twig beetle.

Audley, who conducts his research in a commercial orchard near Winters, investigates behavioral chemicals that repel the walnut twig beetle from landing on English walnut trees. The walnut twig beetle (Pityophthorus juglandis), in association with a canker-producing fungus, Geosmithia morbida, causes the insect-pathogen complex known as thousand cankers disease.

 “The disease threatens both native black walnuts across North America and agriculturally important English walnut, particularly in California,” said Audley, who received the $1000 award at the recent conference in Anchorage. “My research focuses on improving our understanding of the walnut twig beetle's chemical ecology and developing a semiochemical repellent tool to manage the threat.”

The scholarship memorializes Mark Duane McGregor, a bark beetle management specialist who died in April 1990 while conducting forest entomology research in Idaho. The scholarship has since expanded to honor other deceased WFIWC members.

Audley, on a path to receive his doctorate in entomology by December 2019, is co-advised by Steve Seybold, 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; Associate Professor Louie Yang of the UC Davis Department of Entomology and Nematology, and Professor Richard “Rick” Bostock of the UC Davis Department of Plant Pathology. The Bostock lab is heavily involved with the chemistry side of Audley's repellent research. Seybold and Bostock have shared a California Department of Food and Agriculture grant with the doctoral student.

Audley is invited to deliver a plenary lecture on his dissertation at the WFIWC meeting next year in Calgary, Alberta.

Audley, who was born in Washington D.C., but spent most of his childhood in Atlanta, Ga., was first introduced to forest entomology while he was a student 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 then received 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 (WTB) in cut black walnut logs, live edged boards, and nursery stock. He joined the UC Davis doctoral program in September 2015.

“My academic and work history have shaped my interest in researching invasive bark and wood boring beetles,” Audley said in his award application. “I am fascinated with the biology and ecology of these invaders and their interactions with native, often naïve host trees. My plan is to continue to pursue research pertaining to the ecology and management of invasive bark and wood boring beetles, focusing on chemical ecology and semiochemical disruption.”

His research at UC Davis includes conducting field-based research relating to the chemical ecology of WTB in northern California walnut orchards and native riparian forests; assisting on several WTB-related research projects, including a trial on the efficacy of emamectin benzoate in protecting walnuts from WTB and thousand cankers disease (TCD), and a project assessing the impact of WTB and TCD on the productivity of English walnut orchards in California. In addition, Audley has monitored and sorted the trap catches from numerous walnut twig beetle flight intercept traps, maintained year round in northern California and performs sorting and identification for similar traps maintained by the Tennessee Department of Agriculture.

Active in WFIWC, Audley delivered a presentation on the walnut twig beetle in 2018 as part of an invasive species symposium. He also serves as the student representative on the Founders' Award Committee. At UC Davis, he teaches and mentors students on forest entomology.

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.”

If you've ever walked into the courtyard on the 100 block of E Street in downtown Davis, Calif., you've probably noticed the massive black walnut tree near Sophia's Thai Bar and Kitchen.

It's about 150 years old, 50 feet in height, and measures about five feet in diameter. And it's dying.

What's killing it is thousand cankers disease (TCD), an emerging insect-fungus complex.

It's killing a lot of black walnut trees.

In fact, TCD has caused profound damage to black walnut trees not only in urban areas of California and other western states, but in Pennsylvania, Tennessee and Virginia, according to a newly published review by UC Davis-affiliated scientists and their colleagues. 

The article, “Status and Impact of Walnut Twig Beetle in Urban Forest, Orchard and Native Forest Ecosystems,” published in the Journal of Forestry, updates the spread of the disease, and chronicles the role of the bark beetle, Pityophthorus juglandis, and the canker-producing fungus, Geosmithia morbida, in killing walnut trees, especially black walnuts.

Native to southwestern United States and northern Mexico, the bark beetle, about half the size of a grain of rice, “has invaded urban, orchard and native forest habitats throughout the United States, as well as Italy,” said lead author and forest entomologist Steven Seybold of the Pacific Southwest Research Station, USDA Forest Service, Davis, and a lecturer and researcher with the UC Davis Department of Entomology and Nematology.

Walnut twig beetles (WTB) tunnel into branches and trunks of walnut (Juglans) where they create galleries for mating and reproduction. They carry spores of the fungus into their galleries, and the resulting fungal infection causes formation of cankers, which coalesce and girdle branches and stems.

Between 2005 and 2016, the disease killed nearly 60 percent of the 210 specimens of southern California black walnut mature trees in the USDA Agricultural Research Service's National Clonal Germplasm Repository Juglans Collection near Winters, Seybold said. “This is only an estimate and the true proportion of the mortality is likely much higher, as only six of the 210 trees were rated as having healthy crowns in August 2016." 

“The walnut twig beetle is a significant pest of very large trees because it sequentially attacks the small branches--though ironically not the twigs--all the way down the trunk to the soil line,” said Seybold, a pioneering scientist of TCD, who first found TCD evidence in Davis in 2008. “Most bark beetle species are not this thorough in using all of the phloem tissue in their plant hosts. In Davis right now, in the courtyard next to Sophia's Thai Restaurant, 129 E St, the tiny beetle is gradually killing the largest northern California black walnut tree in the city.  It has taken nearly a decade, but the crown of the massive tree is nearly completed killed.”

Seybold estimated that the E Street tree is about 150 years old, "maybe older." It measures almost 65 inches or just over five feet. 

“The walnut twig beetle is also significant because it is the consummate invasive species; it is small enough to travel under the bark of modest-sized pieces of barked wood and it can withstand relatively dry conditions that it might encounter during transit,” Seybold said. “We believe that it has moved from isolated Arizona black walnut trees along creeks and rivers in the desert Southwest to nearly the entire western USA wherever walnut trees of any species have been planted or grew naturally. It has also been transported to Europe and established significant populations in Italy.”

Seybold noted that the disease is “unique because of its multifaceted negative impact on walnut trees involved in landscaping, food production, and forestry.  Walnut trees are valuable ecologically and for food and timber, so the walnut twig beetle is a good model in which to study the impact of a bark beetle on forest and agro-ecosystem services.” 

The five co-authors of the synthesis article include Stacy Hishinuma and Andrew Graves, two USDA forest entomologists with UC Davis connections. Hishinuma, who works in the Pacific Southwest Region, San Bernardino, and holds a doctorate in entomology from UC Davis, studied in the Seybold and Mary Lou Flint labs, UC Davis Department of Entomology and Nematology. Graves, who works in the Southwestern Region, Albuquerque, N.M., is a former postdoctoral fellow in the UC Davis Department of Plant Pathology.

Other co-authors are Professor William Klingeman III of the Department of Plant Sciences, University of Tennessee, and forest entomologist Tom Coleman with the USDA Forest Service's Southern Region, Asheville, N.C..

UC Davis doctoral student Jackson Audley of the Seybold lab and  Richard Bostock lab (Plant Pathology), contributed  photos of dead and dying walnut trees in the Davis area, along with UC Davis doctoral student Corwin Parker and Hishinuma. Audley, who is researching an ensemble of behavioral chemicals that repel the walnut twig beetle from landing on English walnut trees, conducts his research in a commercial orchard near Winters.  

“WTB is one of a few invasive bark beetles in North America where expanding distribution and impact have been pronounced enough to affect other species, communities, and ecosystems to the extent that services provided by urban forests, agroecosystems, and wildland areas have been altered,” the co-authors concluded in their paper. “We envision that ecological impacts of WTB will continue to unfold across a wider geographic area to affect various types of key services, i.e., provisioning (e.g., timber and nontimber products); regulating (e.g., air and water quality/quantity, climate regulation); and cultural (e.g., recreation, aesthetics, shade) services.”

Scientists first collected the beetle in North America in 1896 in New Mexico, 1907 in Arizona, 1959 in California, and 1960 in Mexico, but never considered it a major pest of walnut trees until black walnuts began deteriorating and dying in New Mexico in the early 2000s. Walnut tree mortality that occurred in the early 1990s in the Wasatch Mountains of Utah and in the Willamette Valley of Oregon is now attributed to TCD.

“Currently, good cultural practices and sanitation of infested materials are the primary strategies for disease management within orchards and also for prevention of spread of the disease and vector to regions with low rates of infection,” according to the UC Statewide Integrated Pest Management Program  (UC IPM)>

UC IPM recommends that trees with less than 50 percent live crown be removed to reduce the buildup of walnut twig beetles and inoculum in the trunk and larger scaffold branches. "Chemical control with either fungicides or insecticides is not recommended for management of thousand cankers disease," UC IPM says.

Which brings us back to the massive black walnut tree that is dying on E Street in Davis. If it dates back to 1868, that's the year the city of Davis was founded. Its namesake, Jerome C. Davis, owned a stock farm on the site.

Who was in the White House and who was in the California governor's mansion that year?  Andrew Johnson and Henry Haight, respectively.  That was also the year that trustees founded the University of California in Oakland; Clark Kerr became the first president.  And 1868 was the year Memorial Day was first observed in the United States...and when author Louisa May Alcott published the first volume of her coming-of-age novel, Little Women.

The little tree in Davis became of age, too, growing into a giant tree offering shade, shelter and sustenance. Who would have thought that a tiny insect, half the size of a grain of rice, would play a major role in its demise?

If you missed hearing The Entomology Band performing in front of Briggs Hall during the recent UC Davis Picnic Day, not to worry.

They're featured in a recent Entomology Today blog, published by the Entomological Society of America (and written by yours truly) and headlined "Bugs and Beat."

Remember “Flight of the Bumble Bee,” “La Cucaracha,” “Boll Weevil,” and the “The Blue-Tailed Fly?”

Well, move over. Think about the three-cornered alfalfa hopper (Spissistilus festinus) and the male insect organ, the aedeagus.

 A group of seven graduate students in the UC Davis Department of Entomology and Nematology performed such tunes as “E Major Homeboy (Spissistilus festinus),” “Tragedy (of the Clocks),” and “Jackson's Song (Aedeagal Bits),” as well as a cover song, “Island in the Sun” by Weezer.  All are members of the UC Davis Entomology Graduate Student Association, headed by Brendon Boudinot, president.

Graduate student Michael Bollinger of the lab of Frank Zalom (a former president of the Entomological Society of America) composed the first three tunes.

The performance capped a day of insect-related activities that included maggot art, cockroach races, nematode identification, scavenger hunts, and honey tasting. Bugs rule!

Meet the septet:

• Molecular geneticist and drummer Yao “Fruit Fly” Cai of the Joanna Chiu lab dressed in a fruit fly costume (Drosophila melanogaster), which he described as “our favorite model organism in Insecta!”
• Bark beetle specialist and rhythm guitarist Jackson “Darth Beetle” Audley of the Steve Seybold lab portrayed an Asian longhorned beetle (Anoplophora glabripennis).
• Honey bee researcher and bass guitarist Wei “Silverfish” Lin of the Brian Johnson lab wore a costume that celebrated his moniker (Lepisma saccharina), a small, wingless insect in the order Zygentoma.
• Ant specialist and keyboard artist Zachary “Leptanilla” Griebenow of the Phil Ward lab dressed as “a generic male leptanilline ant (Formicidae: Leptanillinae).” However, he noted “the yellow color is not anywhere near so vivid in real life.”
• Systematist and tenor saxophonist Jill “Jillus Saximus” Oberski of the Phil Ward lab dressed as a “generalized heteropteran,” which she described as “most likely a member of the family Acanthosomatidae (shield bug) or Pentatomidae (stink bug). My family and friends have called me Jillybug, so I came to be the band's representative of Hemiptera.”
• Molecular geneticist and vocalist Christine “The Clock” Tabuloc of the Joanna Chiu lab wrapped herself in butterfly wings.
• Ant specialist and bass guitarist Brendon “Hype Man-tis” Boudinot of the Phil Ward lab dressed in a green helmet, a blue and gold EGSA bee shirt, and a UC Davis cow costume to showcase his department and campus-wide love of bovines.

The seven band members share a love of music.

Drummer Yao Cai, who grew up in Southeast China and holds an undergraduate degree in plant protection and a master's degree from China Agricultural University, has been playing drums since age 17. “We formed as a short-lived band for a show. After that, I realized that I really wanted to keep playing and improved my drum techniques. Thus, we started another band in college and played for six years in college, as an undergrad and graduate student.

“We were all agriculture-related majors and we mainly wrote original songs,” recalled Cai. The campus concerts sometimes drew a thousand spectators. “After we graduated from graduate school, we stopped. I really missed the time playing drums with folks since I came to UC Davis. Fortunately, after a ‘gap year,' Jackson, Michael and I started jamming in September 2017. Later on, our current talented members joined.”

“It is very interesting that I was in a band that was the first band in Department of Entomology in China Agricultural University and now we started the first band in Department of Entomology at UC Davis,” Cai added.

Rhythm guitarist Jackson Audley said he “started learning to play the guitar when I was about 11 or 12-ish. The first band I joined was a Blink-182 cover band, in which I played the bass guitar, and we played together for most of eighth grade. Then in early high school I joined a Smashing Pumpkins/Radiohead cover band as the second guitarist. Shortly after joining that band, we started making predominantly original music. By the end of high school, we had played a few small shows around the Atlanta area and had recorded a few songs. Unfortunately, the band did not survive the transition into university and we broke up.”

Since then he's mostly played “for fun, and I like to jam with folks.”

Jill Oberski, a native of Twin Cities, grew up mostly in Chaska, “a sleepy suburb of Minnesota.” She received her bachelor's degree in Macalester College in Saint Paul, Minnesota, where she double-majored in biology and German studies.

“I started playing the piano in kindergarten and switched to saxophone in fifth grade,” Oberski related. “I played classical and jazz in my school bands from sixth grade through college and pit orchestra, pep band, and marching band in high school as well. I've always been better at classical than rock, jazz, or Latin.”

“I probably reached my highest point in late high school, when I served as co-section leader for the saxes in the Minnesota all-state symphonic band,” Oberski said. “We even got to play a concert in Minneapolis' orchestra hall. These days I'm only involved in the entomology band and some very casual ukulele playing.”

Keyboard artist Zachary Griebenow, a native of Richmond, Kentucky—he grew up in Kentucky and holds a bachelor's degree in entomology from The Ohio State University—said, “I took piano lessons for a cumulative total of seven years, ages 8 to 17. I performed at least biannually in studio recitals. My primary musical interest is composition, an activity that has not quite received its due on account of my prioritizing systematic entomology. I had never performed in a group prior to joining this band and greatly appreciate the novel experience of doing so.”

Brendon Boudinot, who received his bachelor's degree in entomology at the Evergreen State College in Olympia, Washington, performed on a metallic sky-blue bass and served as emcee. “I just love art,” said Boudinot, president of the UC Davis EGSA. “Music is a family thing for me in a number of different ways. Although I have played instruments alone or in groups for many years, nothing really clicked in me until I heard Michael and Yao play together. They shred.”

Vocalist Christine Anne Tabuloc, who grew up in the Los Angeles area and received her bachelor's degree from UC Davis in biochemistry and molecular biology, says she does not play an instrument. “I'm far less talented than everyone else in the group,” she quipped. “I've been singing for as long as I can remember. I've been writing lyrics since elementary school. However, I never got around to getting music written for them. I was in choir before and have had solos but that's pretty much it.”

Bass guitarist Wei Lin, who grew up in Xiamen, “a beautiful island in southern China,” received his bachelor's and master's degree at China Agricultural University, majoring in plant protection and entomology. “This was my first experience in a band. I just started to learn bass last year when this band was built.”

Following the four-set gig, Boudinot told the appreciative crowd, “That's all we know!”

Pending performances? “The band,” he said, “is on hiatus.”

Or diapause.

(Editor's Note: Listen to a clips of their music on YouTube.)

So tiny and so destructive.

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 dbneale@ucdavis.edu.