- "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 host selection behaviour of the walnut twig beetle, Pityophthorus juglandis, was assessed by monitoring the landing rates of the beetles with sticky sheet traps on the host and nonhost hardwood branches.
- Sticky sheet traps were deployed for 8 weeks from 6 June to 2 August. 2017 in the Putah Creek Riparian Reserve, Davis, CA. Branches from host northern California black walnut, Juglans hindsii, were paired with branches from six nonhost hardwood species.
- The landing rate of P. juglandis (412 beetles trapped/8 weeks; 389 on host branches, 23 on nonhost branches) was significantly greater on the host branches for all nonhost hardwoods except Populus fremontii. Proportional comparisons of beetle presence also revealed a significant preference for the host branches compared with all but two nonhost species, Acer negundo and P. fremontii.
- Capturing P. juglandis without the use of an aggregation pheromone was a rare event, underscoring the difficulty of studying the initial phases of host selection behaviour in bark beetles. Unbaited funnel traps adjacent to selected host trees in the experiment only captured five individuals over a 19‐week period. None were captured in traps adjacent to nonhost trees.
- This study provided evidence that P. juglandis discriminates between host and nonhost branches while in‐flight. This directed flight behaviour is likely informed by the recognition of both host and nonhost volatile cues.
- This study established an ecological context for the development of a semiochemical‐based repellent system for protecting walnut trees from future attacks from this invasive bark beetle.
Second Paper: Walnut Twig Beetle Landing Rates
- Host selection behaviour of the walnut twig beetle (WTB) among hardwood trees was investigated in a riparian forest in northern California by monitoring the landing rate of the beetle with sticky traps on branches baited with 3‐methyl‐2‐buten‐1‐ol, the male‐produced aggregation pheromone.
- The assay was conducted over 7 days (22 May to 29 May 2017) and compared landing rates on branches of six nonhost species paired with northern California black walnut, Juglans hindsii (the host).
- A total of 2242/1192 WTB were collected on branches of host/nonhost pairs, and more WTB landed on J. hindsii than on nonhosts in 42 of 58 instances. Female landing rate generally exceeded male landing rate, which underscores the influence of the male‐produced synthetic pheromone in this system.
- Landing rates of WTB males, females, and the combined sexes on boxelder, Acer negundo, and valley oak, Quercus lobata, did not differ significantly from the landing rates on J. hindsii, suggesting that these two nonhost riparian hardwoods do not repel WTB (in the context of the aggregation pheromone).
- Significantly fewer WTB landed on Oregon ash, Fraxinus latifolia, river red gum, Eucalyptus camaldulensis, Fremont cottonwood, Populus fremontii, and red willow, Salix laevigata, than on J. hindsii, which suggests that these four nonhosts may repel one or both sexes of WTB in the context of the aggregation pheromone. Future analysis of the volatiles from these four hardwood species may lead to the discovery of semiochemical repellents for WTB.
Co-authors (in addition to Audley, Homicz, Seybold and Bostock) are Yigen Chen, Foundation Research, Analytics and Business Applications, E. & J. Gallo Winery, Modesto, Calif.; and scientist Catherine Tauber, UC Davis Department of Entomology and Nematology, and formerly with the Department of Entomology, Cornell University, Ithaca, N.Y.
Audley is now a postdoctoral fellow funded by the Oak Ridge Laboratories, and based at the USDA Forest Service, Pacific Southwest Research Station, Davis. While at UC Davis, Audley investigated behavioral chemicals that repel the walnut twig beetle from landing on English walnut trees. He conducted his research in a commercial orchard near Winters. He received the 2019 Western Forest Insect Work Conference (WFIWC) Memorial Scholarship Award for his research on the chemical ecology of the walnut twig beetle. He holds a master's degree in forestry (2015) from the University of Tennessee, and a bachelor of science degree in wildlife biology and natural resource recreation and tourism (2009) from the University of Georgia.
Homicz, who joined the UC Davis doctoral program in September 2019, received a bachelor of science degree in animal biology with an emphasis in entomology (2018) from UC Davis. Her practicum: "Landing Behavior of the Walnut Twig Beetle on Host and Non-Host Hardwood Trees Under the Influence of Aggregation Pheromone in a Northern California Riparian Forest." She holds associate degrees in both biology and natural sciences (2016) from Shasta College.
For more information on the walnut twig beetle and thousand cankers disease, see the UC Statewide Integrated Pest Management Program website.
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, who expects 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.”
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."
Seybold estimated that the E Street tree is about 150 years old, "maybe older" and around 50 feet in height. It measures almost 65 inches--or just over five feet--in diameter.
“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.”
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.
But have you ever heard of a song featuring the three-cornered alfalfa hopper, Spissistilus festinus, and another one spotlighting the male insect organ, the aedeagus?
And composed by a graduate student at the University of California, Davis, and performed by seven insect-attired UC Davis doctoral students?
That's what happened during the recent UC Davis Picnic Day celebration when the septet gathered in front of Briggs Hall to perform three songs composed by talented musician and entomologist Michael Bollinger, enrolled in the master's degree program, UC Davis Department of Entomology and Nematology. The group performed Bollinger's compositions, “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.
The performance went well. Very well. So did Picnic Day.
“My goal was to make sure Picnic Day worked overall, and that, for the band, the sounds were balanced and each of the elements could be heard,” said emcee and band member Brendon Boudinot, president of the UC Davis Entomology Graduate Student Association (EGSA) and a doctoral candidate specializing in ant evolution and classification.
The “Entomology at UC Davis” exhibit at Briggs Hall, the work of the UC Davis Department of Entomology and Nematology, won the campuswide “At One With Nature” category. And the band? It drew loud applause and high praise from the standing crowd.
Their name: “The Entomology Band.” (No take-offs of the iconic “Beatles,” “Buddy Holly and the Crickets” or “Adam and the Ants.”)
Bollinger's original songs capped a day of insect-related activities that included maggot art, cockroach races, nematode identification, scavenger hunts, and honey tasting.
- 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).” He said: “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.
“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.”
Rhythm guitarist Jackson Audley said he “started learning to play the guitar when I was about 11-12 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, Minn., “a sleepy suburb of Minnesota.” She received her bachelor's degree in Macalester College in Saint Paul, Minn., 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 / marching band in high school as well. I've always been better at classical than rock/jazz/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--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.”
Brendon Boudinot, who received his bachelor's degree in entomology at the Evergreen State College, Olympia, Wash., performed on a metallic sky-blue bass. “I just love art,” he said. “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.”
“The Entomology Band is special to me, and I am just glad I could be a part of it.”
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 in 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.”
The seminar takes place from 4 to 5 p.m. in Room 3001 of the Plant and Environmental Science Building.
Audley is presenting a preview of his thesis project in the UC Davis Forest Biology Research Center Seminar Series.
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”
All seminars will be held at 4 p.m. in Room 3001 of the Plant and Environmental Science Building. For more information, contact David Neale at firstname.lastname@example.org.