Donald Lewis McLean
Professor of Entomology, Emeritus
After receiving his Ph.D., Don joined the University of California (UC) faculty as a Junior Entomologist and conducted research on insect vectors of plant pathogens at the UC agricultural research station in Salinas, CA. In 1959, Don hired Marvin Kinsey as a technician, thus beginning a working relationship and friendship that lasted throughout Don’s career at UC Davis. In 1964, when the Salinas research station closed, Don and Marv were assigned to the UC Davis campus where Don’s research program continued to focus on insect vectors of plant pathogens. His efforts ranged widely, including investigations of aphids, leafhoppers, and psyllids as vectors of plant pathogenic viruses, phytoplasma, and bacteria. He was especially interested in vector and pathogen interactions related to acquisition, location in the insect, and ultimately inoculation to new hosts.
In his quest to understand how aphid feeding behaviors occurred inside plant tissues, acquired the plant pathogen, then inoculated into in a new plant host, Don led a collaborative effort to develop an electronic monitoring system to reveal these hidden feeding activities that he hypothesized were critical to plant pathogen transmission. In brief, he applied electricity to a plant substrate (whole plant or a leaf). He then placed a piercing-sucking insect, such as an aphid, on a gold wire attached to an amplifier and strip-chart recorders, and allowed the insect to feed on the plant. The insect’s mouth parts piercing the plant and their subsequent feeding activities resulted in distinctive waveforms that Don and collaborators were able to correlate to behaviors within the plant tissues. This audacious and creative venture proved abundantly fruitful, and Don reported the first results in the journal Nature in 1964. The electronic feeding monitor, gave rise to an entirely new science of entomology, electropenetrography (or EPG). The instrument, now called an electropenetrograph or EPG monitor, captured the imaginations of scientists worldwide, and research using this new technology abounded. In the more than 5 decades that have passed, EPG monitors have evolved, by taking advantage of the electronics revolution over those years, advancing through multiple new technologies. Using protocols that Don published to correlate specific insect behaviors with electronic waveforms, hundreds of scientists have worked to reveal the feeding behaviors of many species of piercing-sucking insects. Their work built upon and fulfilled Don’s prescient prediction about the importance of specific activities to pathogen acquisition and inoculation. The magnitude of this contribution to advancing our understanding of insect vector feeding and the intimate interactions between the insects, pathogens, and plant hosts cannot be overstated. As one of Don’s former graduate students, Elaine Backus, noted in the Proceedings of an Informal Conference in his honor at the 100th Annual Meeting of the Entomological Society of America, “This electronic monitoring system, more than any single development, has revolutionized the study of piercing and sucking insects.”
Always ready to push the boundaries of technology to gain an in-depth understanding of insect vector-plant pathogen interactions, Don’s laboratory was one of the first to use electron microscopy on the UC Davis campus. By the 1970s, his laboratory was deeply engaged in investigating the endosymbionts of aphids, using light and electron microscopy to describe this important insect-microbe interaction. This research revealed the specialized cells in which aphid symbiotic bacteria live (mycetocytes) and laid the groundwork for some of the first investigations of symbiont genomes and specific relationships with particular aphid species. Don encouraged graduate student Alexander (Sandy) Purcell, to apply for a Graduate Student fellowship to do research on a “virus” disease of grapevines called Pierce’s disease. Because of this groundbreaking research, we learned that a bacterium transmitted by leafhoppers causes this disease, not a virus, as was thought for decades prior to this work. Sandy also recalls how Don later encouraged him to apply for a faculty position at Berkeley, where he was able to continue his vector research for a time that spanned 47 years. Don encouraged his students to work independently and explore difficult questions in vector biology. Elaine discovered chemosensory structures in the precibarium of leafhoppers, successfully severing the nerves to specific chemosensilla and demonstrating the role of these gustatory sensory structures in leafhopper feeding behavior. Similarly, he encouraged graduate student Diane Ullman to explore the role of psyllids in transmitting the putative causative agent of pear decline and to conduct the first EPG monitoring studies with this insect. Elaine and Diane remember Don’s encouragement to follow these lines of research, in spite of their difficulties, and his support of Marvin Kinsey in providing the essential technical expertise needed to succeed in these scientific endeavors.
Don’s contributions to the field of entomology and to the sciences were recognized with his election as a Fellow of the American Association for the Advancement of Science (1983), a Fellow of the Entomological Society of America (ESA) (1990) and an Honorary Member of the ESA (1992). While Don made important contributions to the field of vector-borne plant pathogens, he was also an outstanding leader, devoting himself to several administrative posts that were locally and nationally significant. Don was chair of the UC Davis Department of Entomology (1974-1979). His colleague, emeritus professor Robert Washino recalls that during his tenure as department chair, “Don built collaboration and collegiality in the Department of Entomology when he strongly encouraged all faculty, staff and students to participate in daily coffee breaks in the Departmental conference room. These gatherings maximized social exchange amongst the different laboratories and encouraged diverse teaching and research activities. This was especially important because the department had moved into Briggs Hall where offices and laboratories were spread throughout the building and even into separate buildings. More than any other Chair up to that point, he also strongly urged full participation of faculty and students, especially the latter, in professional meetings at regional, national and even international sites.” Don felt strongly that entomology was an important biological science and that development of a Division of Biological Sciences would enhance and elevate many opportunities for the entomological sciences. This was a courageous point of view, as the Davis campus strongly identified with the agricultural sciences. Speaking volumes about his convictions and leadership, Don was the first Dean of the burgeoning UC Davis Division of Biological Sciences (1979-1986), a successful venture that ultimately led to formation of the current College of Biological Sciences at UC Davis.
Nationally, Don served the Entomological Society of America (ESA) as a member of the governing board for many years in the 1970s and 1980s. In 1984, he was elected President, and then the following year (1985) as Secretary-Treasurer. Elaine says of Don’s service to the ESA, “In his activities in ESA, McLean is best remembered for helping to diversify the then-mostly white, male, agriculture-dominated membership of the Society.” Some of the traditions he instituted to help women integrate into the society still remain important, i.e., the Women in Entomology Breakfast at national meetings, first held in 1984 with Don and six other participants. In the years since, the Breakfast has grown to a major ESA event, with many dozens of participants, both women and men. He retired from UC Davis in 1987, becoming Dean of the College of Agriculture and Life Sciences at University of Vermont, where he served for 5 years before retiring and returning to California.
Don was the third of a five-generation line of vector biologists at UC Berkeley starting with Henry H.P. Severin who mentored Julius H. Freitag, who then mentored McLean. McLean mentored Sandy Purcell, who, as a faculty member at Berkeley mentored Rodrigo Almeida, now a faculty member at Berkeley mentoring a new generation of vector biologists. There is no doubt that this legacy and the impact of the vector biologists Don helped train will continue for additional generations. He was fiercely committed to bringing change to the world of entomology, encouraging expansion into physiology and molecular biology. His leadership brought important changes to the Department of Entomology and to the UC Davis campus. He saw potential in each of his students and gave them space to become highly independent and creative scientists. He enjoyed a full and successful life with his family and many cherished friends. His faculty colleagues share fond memories of Don, as both a colleague and a scientist. Don was an outdoorsman who enjoyed camping with his family, backpacking, playing many sports throughout his life and was an avid Red Sox Fan, fisherman and photographer.
Don’s contributions to science, in particular through invention of EPG science for “seeing” the invisible actions of insect vector feeding inside plant tissues and cells, have left a rich legacy.
Elaine Backus
Al Grigarick
Harry Kaya
Alexander (Sandy) Purcell
Diane Ullman
Robert Washino
