David Lee Wood

David Lee Wood had a long, highly productive, and impactful association with the University of California, Berkeley. He was appointed Assistant Professor in the Department of Entomology in 1960, Associate Professor in 1966, then Professor of Entomology in 1970. From 1983 to 1985, he was Associate Dean in the Graduate Division, was appointed Chairman of the Department of Entomological Sciences from 1985 to 1990, and Chairman of the Department of Conservation and Resource Studies from 1991 to 1993. Following retirement in 1994, he held the title Professor of the Graduate School. Although officially retired, he scarcely slowed down until a few years prior to his passing at age 93 on February 10, 2024, in Moraga, California.  

David was born January 8, 1931 in Elmira Heights, New York. He earned a BS degree in Forestry from Syracuse University College of Environmental Science and Forestry in 1952. After college, he served in the US Army following Officer Candidate School training, leading surveying teams for the Army Corps of Engineers in Alaska and the southern California desert. Following his service, in 1955 he enrolled in the PhD program in entomology at the University of California, Berkeley, working with Professor Ray Smith.

In the late 1950s, the factors that led to bark beetle outbreaks in western conifer forests were poorly understood. One result of large-scale logging in coniferous forests across western North America was a shift to younger, even-age trees, a change that was recognized as a major factor in predisposing these forests to bark beetle outbreaks. The absence of mechanistic explanations for why some bark beetle species transition from low population levels to mass-attacks on host trees hindered efforts to control outbreaks.

David’s dissertation research tested predictions of the Hopkins host selection principle, which proposed that adult herbivorous insects preferentially select as hosts the species in which they developed as larvae, using as an experimental system the California five-spined ips bark beetle, Ips paraconfusus, and its orientation responses to bolts of three co-occurring tree species; ponderosa pine, sugar pine, and Jeffrey pine. These experiments showed that, instead of a preference for the larval host, orientation to and attacks on susceptible trees appeared to be due to detection of direction of volatile compounds. Failure to experimentally confirm that bark beetle behavior was consistent with the Hopkins host selection principle led to a search for alternative explanations for host selection.

Working under the auspices of the Boyce Thompson Institute, David and Jean-Pierre Vité established that “primary attraction” of Ips paraconfusus to ponderosa pine trees was correlated with low oleoresin exudation pressure (o.e.p.), which affects the ability of this tree species to expel beetles tunneling through the bark. Subsequent work by others showed that o.e.p. was not a consistent factor in mass attacks, suggesting the presence of other, yet unrecognized influences on the behavioral shift from initial attacks to mass attacks. The Vité and Wood o.e.p. work introduced the concept of “secondary attraction,” wherein it was not initially clear what mechanism stimulated the mass attacks seen following initial host selection by the pioneering beetles. These studies led to the realization that the truly important research question was the story behind secondary attraction, which led to David’s pioneering research that discovered the world of bark beetle pheromones.

Indeed, volatiles from the mixture of beetle frass and wood debris produced by tunneling male Ips paraconfusus were found to be attractive to females. In collaboration with Milt Silverstein, a chemist at the Stanford Research Institute who specialized in identification of natural products, 4.5 kilograms of this material were extracted with solvents, from which several compounds were isolated, identified, and synthesized in the lab. When these compounds were assayed for the anticipated behavioral responses, however, none of the three individual compounds was attractive alone. Further bioassays led to the finding that a multi-component mixture, in specific ratios, was necessary to elicit behavioral responses. The term pheromone had only recently been introduced (1959) and David and colleagues were among the earliest researchers to explore the roles that these previously unrecognized chemical compounds might play in insect-tree interactions. This was the first evidence for a multi-component pheromone system in any insect species. The team of Wood and and Silverstein went on to identify the aggregation pheromone of the western pine beetle, Dendroctonus brevicomis, and added to their collection of pioneering discoveries, including identification of bicyclic ketals as a new class of semiochemicals, the first demonstration of synergism between a host kairomone and an insect-produced pheromone, and the first discovery of interspecific communication among insects.

In addition to his work with attractive/aggregation pheromones, David and his students William Bedard and Paul Tilden elucidated the role of a different type of pheromone, verbenone, in shutting off the aggregation response of western pine beetle to its own aggregation pheromone once the host has been fully colonized. These “epideictic” or anti-attractant pheromones have been dubbed “no vacancy signals” because they direct responding beetles away from the newly colonized tree, the source of the aggregation pheromones. Their work led to the development of techniques for protecting individual pines from beetle attack by stapling multiple verbenone-releasing packets onto the tree trunks to prevent mass attack by bark beetles.

These basic discoveries led to searches for other pheromone systems and subsequently to the application of synthetic bark beetle pheromones for area-wide suppression of beetles to protect forests from mass attack. Today, baits that incorporate these and other beetle pheromones are commercially available for both monitoring and controlling bark beetle attacks.

The crucial role played by David Wood in advancing the emerging field of integrated pest management (IPM) into the realm of forest entomology is well expressed by  Bob Coulson of Texas A&M University, capturing the essence of the era:

“Dave Wood was my Captain at the onset of the Golden Age of forest entomology in North America. He later became my dear and cherished friend and colleague in the joyous profession for which we shared a common passion.

In the early 1970’s forest entomology was beginning to transition from a “cottage industry” into a significant and lavishly funded (by previous standards) research enterprise. Bark beetle outbreaks in the West and South served as the catalysts that triggered State and Federal involvement. Dave and colleagues at Cal and the USDA Forest Service were at the forefront of this new era. Because of his natural leadership ability, earned respect for his technical knowledge, collegial demeanor, and temperate personality, Dave was the political spokesperson for the group. In this capacity, Dave invited me (and my career-long and valued friend, Tom Payne) into the arena.

Tom (Texas A&M University) and I (Texas Forest Service) were both ambitious and highly motivated to be successful in our new positions and recognized that there was strength in partnership. However, neither of us had worked on bark beetles and we were at best “potentials” as research entomologists. Dave anticipated that the bark beetle outbreaks in West and South were of sufficient magnitude to warrant inclusion in this new IPM era and that allies in the South, addressing the southern pine beetle, would strengthen a proposal for targeted research on the western pine beetle and the mountain pine beetle.

In the summer of 1972, at his expense, Dave invited Tom and me to Berkeley to meet the community of entomologists, students, and post-docs associated with the forest entomology program at Cal and his partners in the USDA Forest Service, PSW.  Without challenge (then and now), this program was the best and most talent-diverse group that had ever been assembled to conduct research in forest entomology. Dave’s planning for the visit was insightful and kind-hearted as he provided time and opportunity for us to have technical exchange, social interaction, and a cultural experience with Berkeley and the Bay Area. The meeting flanked both sides of the weekend. We first met in Berkeley, were ‘tourists’ and ‘socialites’ over the weekend, and then traveled to McCloud Flats to observe Dave’s field pheromone-based experiment on the western pine beetle. On this visit, we met and interacted technically and socially with the personalities connected with the forest entomology program who graciously shared all details regarding their work. This profound experience provided the model that I used in establishing my research program on population dynamics of the southern pine beetle in Texas.

Dave’s generosity and thoughtfulness in providing the remarkable experience was the beginning of a career-long scientific exchange and social interaction for us. His insight regarding bark beetles and IPM was rewarded when we prospered under the first forest entomology “Big Bug” research project.

As an anecdote to the science side of the story, Tom and I had a serendipitous encounter with our host and his spouse, Caroline. On a pleasant and sunny Saturday morning in Berkeley, we were walking along Telegraph towards the campus. I was photographing the “wildlife,” when Dave and Caroline (whom we had not met) drove up in their Alfa Romeo sports car. The greeting was as if we had been life-long friends, which we became.”

The program David was chosen to lead was a component of a large multidisciplinary, multiyear project aimed at developing methods to control pests of major agricultural systems, sponsored by NSF, EPA, USDA, the California Agricultural Experiment Station, and California IPM. This project tested the efficacy of deploying attractant aggregation pheromones to trap bark beetles in mass numbers, with the goal of reducing population sizes below outbreak levels. Thus, his earlier work on identifying the mechanisms that led to bark beetle attraction to conifers became the foundation for landscape-scale projects designed to suppress the destructive epidemics of bark beetles that caused enormous losses of timber. The promise of mass trapping to eliminate outbreaks was confounded, however, by the difficulties inherent in the use of attractant aggregation pheromones, i.e., the risk of attracting beetles into surrounding untreated stands and the complexities of fine-tuning the aggregation response to avoid incidental tree mortality. David’s work thereafter shifted emphasis from the use of aggregation pheromones to the use of the anti-aggregation pheromone verbenone, whose role in terminating bark beetle aggregation he and his students had defined earlier.

In the early 2000s, David and his former student Nancy Gillette conducted a series of large-scale studies testing the theory that verbenone and MCH (ethylcyclohexanone, another antiaggregation pheromone) could effectively protect entire stands of trees when deployed as many small point-source release devices, rather than as packets stapled to trees for single-tree protection. Their work was supported by the development by industry colleagues of biodegradable pheromone-releasing “chips” that could be applied from aircraft or manually using fertilizer spreaders. These chips provided a slow-release mechanism that could sustain pheromone levels during the primary flight periods of several of the bark beetle species. Early results proved that the chips could be applied without a liquid sticker and would still release effective rates of the pheromones after landing on the forest floor, which vastly simplified the application process. Over the course of several years in a series of studies conducted in collaboration with forestry professionals and US Forest Service Forest Health entomologists, they demonstrated that this method was effective in reducing area-wide bark beetle attack in lodgepole pine, whitebark pine, limber pine, and Douglas-fir. This achievement was the realization of David’s long-standing dream of exploiting the beetles’ own pheromones to protect forest stands over very large scales.

As an entomologist, David always had a keen appreciation of the complex impacts of both insect pests and pathogens on trees. So much so, that over the years he had very important collaborations with UC Berkeley forest pathologists Fields W. Cobb and John R. (Dick) Parmeter on the relationships between two important indigenous root and bole diseases of conifers caused by the fungal pathogens Heterobasidion annosum and Leptographium wagenerii and various species of bark beetles and weevils. This merging of forest pathology and forest entomology represented a new area of interdisciplinary research. Emerging diseases of native California trees caused by introduced pathogens was a later focus of his research interests. He and colleagues published a number of research papers on pitch canker, an introduced disease of Monterey pines caused by Fusarium circinatum, in close collaboration with Professor Tom Gordon (1951-2021), initially at UC Berkeley and then UC Davis. This research was conducted the close collaboration of a post-doctoral researcher, Andrew Storer (Michigan Technological University). One notable outcome of this research was the demonstration that Monterey pines can express systemic induced resistance (SIR) to the pathogen, leading to reduced pathogenicity upon subsequent reinfection. While still engaged in pitch canker studies, he became involved in studying another introduced pathogen, Phytophthora ramorum, that causes the disease known as sudden oak death. In association with Brice McPherson, a former student and Specialist at UC Berkeley, he established the first long-term monitoring plots to evaluate the effects of this disease on native forest trees, which led to documentation of disease progression in several affected species and the roles of ambrosia and bark beetles in the disease. These studies expanded into collaboration with Enrico Bonello (Ohio State University) that documented resistance to the pathogen in coast live oaks and showed that compounds in the trees’ phloem were quantitative predictors of resistance. In both these epidemics, various bark and ambrosia beetles play significant roles in the diseases and subsequent mortality of infected trees.

A self-professed tree hugger, David’s primary interest was forest health, as impacted by insects and fungi, and the interactions among these factors. His career began in the midst of the emerging field of integrated pest management, IPM, with Berkeley as a center of this approach to controlling pestiferous insects, among other types of organisms. David was advisor to more than 50 masters and doctoral students at UC Berkeley, as well as outside committee member in a number of dissertation committees at other universities. Working with graduate students and postdocs, the subjects studied in the Wood lab ultimately included numerous species of bark beetles, wood wasps, carpenter ants, and subterranean termites. His guidance and career influence were notable regarding studies on subterranean termites. He served as mentor and thesis advisor for five masters and doctoral students, some of whom later became internationally recognized researchers. Together, these former students would publish numerous papers on termites and their control. 

Over a greater than 60-year career, David published more than 150 refereed papers, as well as numerous conference proceedings and book chapters. His 1982 article in Annual Review of Entomology, “The role of pheromones, kairomones, and allomones in the host selection and colonization behavior of bark beetles”, has been cited >1000 times. He published his last paper in 2023, at age 92, with several more posthumous papers in preparation or submitted by colleagues. He edited and co-wrote three books: "Control of Insect Behavior by Natural Products", with Milt Silverstein and Minoru Nakajima, Academic Press (1970), "Integrated Pest Management in Pine-Bark Beetle Ecosystems", with William Waters and Ronald Stark, John Wiley and Sons (1985), and “Pests of the Native California Conifers”, with Thomas Koerber, Robert Scharpf, and Andrew Storer, University of California Press (2003).

Well into his 80s, David was an enthusiastic participant in field work, working in plots for monitoring sudden oak death as well as the multiple pitch canker studies in the Monterey pine forests of Pebble Beach.

During his active faculty time and well into retirement, David was in demand as an expert witness in court cases involving tree failures and imported wood products that harbored non-native insects. Even more impressive, long after David officially retired, he was actively working on a review of the evidence that increasing bark beetle outbreaks are affected by climate change, which although not completed, demonstrates his continuing drive to make a contribution to the field that he helped to advance throughout his career.

David was keenly interested in undergraduate education and was one of the developers of the freshman seminar series at Berkeley, in which small groups of students meet with professors in informal discussions. He taught the same class, Topics in Resource Conservation, for >25 years, until Spring 2022. A highlight of this class was an optional day-long visit to Muir Woods and Muir Beach, which was often the first opportunity students had seen an old-growth redwood forest. Despite his prominence as a professor, David always maintained an open-door policy to his office, ready to talk with any student or colleague who stopped by. In accord with his concern for students, he was active in successful efforts to get UC Berkeley to provide opportunity and accommodations for students whose ability to participate in their education was constrained by disabilities or who were not traditionally provided access to an entomological education or career due to gender or race. David was a champion for opening doors of opportunity for women; he was major advisor to several women graduate students; recruited and hired the first African American faculty member in the Department of Entomology; and graduated the first wheelchair bound master’s student in Entomology, along with securing funding to install wheelchair ramps and power opening doors for an on-campus building and several off-campus facilities.

David was recognized by a number of organizations and institutions, including the Silver Medal from the Swedish Council for Forestry and Agricultural Research (1983), the Silver Medal from the International Society of Chemical Ecology (2001), and the Illustrious Alumni Award – SUNY College of Environmental Science & Forestry, Faculty of Environmental & Forest Biology (2003). He was particularly proud of being awarded the Berkeley Citation in 1995 in recognition of his service by the university to which he dedicated his career. He was elected Fellow of the Entomological Society of Canada (1985) and the Entomological Society of America (1998) and presented the Founders Memorial Lecture at the Entomological Society of America annual meeting (1986).

David Wood is survived by his wife of 64 years, Caroline, daughter Catherine Taylor, son Jonathan Wood, grandchildren Alex Ansari, Joe Wood, Kate Lee, and great-grandchildren McKenna and Kendall Lee.

One measure of a persons’ life is the number of others whose lives were positively influenced. By this criterion, David Wood had an outsized impact on countless students and professional colleagues.

Brice McPherson, Specialist (retired)
Dept. of Environmental Science, Policy, and Management
University of California, Berkeley

Contributions by: John Borden, Bob Coulson, Vernard Lewis, Nancy Gillette, Enrico Bonello, and Andrew Storer
October 2024