Yigen Chen and Steve Seybold continually trapped the reddish-brown insect, about a third of the size of a grain of rice, for three years along Putah Creek in Davis, Calif., and recorded its daily and seasonal flight behavior. They lured the insect into the traps with a synthetic version of its aggregation pheromone.
“We discovered the collective and interactive effects of four environmental factors on the crepuscular (twilight) flight behavior of the insect,” said lead author Chen, a research entomologist and project scientist with the UC Davis Department of Entomology and Nematology. “We found that the optimal trapping conditions are a combination of moderate to warm temperatures, around 79 to 81 Fahrenheit; low light intensity; low wind speed, 0.6 to 2.5 miles per hour; and moderate barometric pressure, 755 to 757.”
“Understanding the walnut twig beetle's seasonal flight cycle and factors that govern its flight are critical first steps in the early detection of invasive species prior to implementing pest eradication or integrated pest management (IPM) programs,” they wrote in their research article, “Crepuscular Flight Activity of an Invasive Insect Governed by Interacting Abiotic Factors,”published in the Aug. 26 edition of the Public Library of Science, PLOS ONE.
However, when coupled with a hitchhiking fungus, Geosmithia morbida, it causes what is known as thousand cankers disease. The beetles create numerous galleries beneath the bark, resulting in fungal infection and canker formation. The large numbers of cankers led to the name, thousand cankers disease.
As the disease advances, the health of the tree declines and eventually it dies, sometimes within a three-year period, said Seybold, who has been studying the beetle and the newly discovered fungus with its barrel-shaped spores since 2008.
When male beetles initiate new galleries, they produce an aggregation pheromone. As the population increases, the flight response of males and females similarly increases.
Mating disruption or interruption of insect aggregation is crucial to controlling such insect pests as the walnut twig beetle in IPM programs, the entomologists pointed out. “Understanding the interactions among abiotic environmental factors on flight activity, should increase the efficacy of these methods in a specific IPM program to control the beetle,” Chen said.
“The primarily crepuscular flight activity had a Gaussian relationship with ambient temperature and barometric pressure but a negative exponential relationship with increasing light intensity and wind speed,” they wrote in their abstract. “A model selection procedure indicated that the four abiotic factors collectively and interactively governed P. juglandis diurnal flight.”
New knowledge of the primary periods of seasonal flight (May‒July and September‒October) “provides some guidance for when semiochemical-based interruption of aggregation may be applied most efficaciously,” they said..
Seybold, one of the first scientists to study the beetle and fungus in California, served on a scientific team that developed guidelines and trapping methods for the beetle. In 2010 and 2011, the team discovered and later patented the aggregation pheromone for the beetle and conducted scientific trials in northern California.
Late in the summer of 2011, the team demonstrated the efficacy of the pheromone as a flight trap bait. The bait lures both male and female beetles into a small plastic funnel trap.
The walnut twig beetle, native to the southwestern United States and Mexico, and widely distributed in Colorado, Arizona, California, and New Mexico, has now been detected throughout much of the United States: in nine western and five eastern states. In 2013, it was reported in northern Italy.
The earliest symptom of thousand cankers disease is yellowing foliage that progresses rapidly to brown wilted foliage, then finally branch mortality. Branch mortality and decline of the tree crown are one of three major symptoms of thousand cankers disease. The others are numerous small cankers on branches and the trunk, and holes and other evidence of tiny bark beetles.
- Thousand Cankers Disease and the Walnut Twig Beetle in California (UC IPM)
- Walnut Twig Beetle (USDA Forest Service)
- Pest Alert, Walnut Twig Beetle and Thousand Cankers Disease (Colorado State University)
- Thousandcankers.com (This site is a collaborative effort between the Northeastern Area State and Private Forestry, the USDA Forest Service Northern Research Station, the Purdue University Department of Forestry and Natural Resources, the Hardwood Tree Improvement and Regeneration Center, the American Walnut Manufacturers Association, and the Walnut Council.)
Hishinuma, who is seeking her doctorate, studies the walnut twig beetle, Pityophthorus juglandis, which in association with a newly described fungus, Geosmithia morbida, causes thousand cankers disease (TCD) of walnut and butternut trees.
Hishinuma works with major professor Mary Louise Flint and is co-advised by chemical ecologist and forest entomologist Steve Seybold of the Pacific Southwest Research Station, USDA Forest Service, Davis, an affiliate of the department. Flint serves as an Extension specialist with the UC Davis Department of Entomology and Nematology and as the associate director for urban and community IPM, UC Integrated Pest Management Program. Both Flint and Seybold plan to attend the conference.
Previous recipients of the annual award have gone on to develop professional careers in forest entomology in academia or with the USDA Forest Service. UC Davis postdoctoral researcher Andrew Graves of Plant Pathology won the award in 2005 while a student at the University of Minnesota.
WFIWC is the core organization for forest entomologists in western North America with membership not only in the United States, but also in Canada and Mexico. The organization was founded in 1949 to provide an informal opportunity for forest entomologists to exchange new ideas and findings prior to each upcoming field season. It established the Memorial Scholarship Fund in 1990 to memorialize member Mark McGregor of the USDA Forest Service and later PheroTech Inc., who died in Idaho while working on research. Other contributions have since honored additional colleagues.
Hishinuma also received two scholarships from the California Garden Clubs, Inc. (CGCI) and a McBeth Memorial Scholarship to support her research on TCD.
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 east of the Mississippi to at least five states in the heart of the valuable black walnut timberlands. Latest statistics show that the beetle and pathogen are now known from nine states in the western U.S. and four states in the eastern U.S. There is a fifth state (Maryland) where only the beetle has been found and a sixth state (North Carolina) where only the pathogen has been found.
Seybold's research group has led the effort to characterize the disease in California and to develop a nationwide detection program for the beetle. Scientists believe that TCD occurs only on walnut, butternut, and wingnut, but it is most damaging to native black walnuts, Juglans californica, J. hindsii, and J. nigra although the disease has been recorded on at least 10 species of walnuts or their hybrids in California. Often the first symptoms of TCD are flagging and yellowing leaves and branch dieback, Seybold said. Affected branches show sap staining and pinhole-sized beetle holes. Beneath the surface are dark stains caused by the fungus.
Seybold, an affiliate of the UC Davis Department of Entomology and Nematology, is a chemical ecologist with the U.S. Department of Agriculture Forest Service's Pacific Southwest Research Station in Davis.
The article, written by Dinsa Sachan, begins: “If you want to keep insects off your crops, you have a couple of options: Spray the plants with pesticides or confuse the bugs with pheromones. The latter—chemicals used by insects to communicate—are more environmentally friendly, but manufacturing them involves harmful chemicals. Now, scientists have devised a method that enables them to produce pheromones from plants themselves, a safer and potentially more economical approach.”
Seybold, who was not involved in the study, was asked to comment on the research and noted: “The work is a ‘breakthrough' and ‘a wave of the future.' It will change the way that commercial pheromone outfits do business and will significantly enhance the quality and potentially lower the cost of the products that they provide."
The research, led by Christer Löfstedt, a chemical ecologist at Lund University in Sweden, dealt with the genetic modification of plants to “make components components of pheromones produced by the bird cherry ermine moth (Yponomeuta evonymella) and the orchard ermine moth (Y. padella),” wrote Sachan. “In the wild, female moths emit these sex pheromones to attract male suitors."
The research, "A Plant Factory for Moth Pheromone Production," is published in Nature Communications. Abstract: Moths depend on pheromone communication for mate finding and synthetic pheromones are used for monitoring or disruption of pheromone communication in pest insects. Here we produce moth sex pheromone, using Nicotiana benthamiana as a plant factory, by transient expression of up to four genes coding for consecutive biosynthetic steps. We specifically produce multicomponent sex pheromones for two species. The fatty alcohol fractions from the genetically modified plants are acetylated to mimic the respective sex pheromones of the small ermine moths Yponomeuta evonymella and Y. padella. These mixtures are very efficient and specific for trapping of male moths, matching the activity of conventionally produced pheromones. Our long-term vision is to design tailor-made production of any moth pheromone component in genetically modified plants. Such semisynthetic preparation of sex pheromones is a novel and cost-effective way of producing moderate to large quantities of pheromones with high purity and a minimum of hazardous waste.
In announcing the awards, Provost Ralph Hexter noted (1) that Tatiossian’s research on the walnut twig beetle makes a significant contribution to establishing an integrated pest management plan; (2) that her manuscript, “Flight Response of the Walnut Twig Beetle, Pityophthorus juglandis, to Aggregation Pheromones Produced by Low Densities of Males”; is in preparation for submission to the Journal of Chemical Ecology; and (3) that her poster received attention at a national entomology conference for the ceramic bark beetle she sculpted.
Hexter presented awards of excellence to Brenda Marin-Rodriguez and L. Carolina Tavarez. In addition to Tatiossian, honorable mentions went to Amanda Steele, biomedical engineering; Rachel Borthwell, biological sciences and art history; and Lindsey Black, history.
A photo of Tatiossian and Black appears as the cover photo on the UC Davis Undergraduate Facebook site at https://www.facebook.com/UCDavisUndergraduateEducation. Her poster, including the ceramic bark beetle she crafted, is mounted on the third floor of Briggs Hall, next to the administration office of the UC Davis Department of Entomology and Nematology.
Tatiossian, who joined the Research Scholars Program in September 2011, graduated from UC Davis in three years (she achieved the top grade point average in entomology) and is currently working in the laboratory of Diane Ullman, professor of entomology and associate dean for undergraduate academic programs in the College of Agricultural and Environmental Sciences.
Among those nominating her or supporting her nomination were her mentor, chemical ecologist and forest entomologist Steve Seybold of the Davis-based Pacific Southwest Research Station, USDA Forest Service, and an affiliate of the UC Davis Department of Entomology; professor Jay Rosenheim who co-founded and co-directs the Research Scholars Program in Insect Biology; and Diane Ullman.
Rosenheim noted that Tatiossian was a member of the first cohort of undergraduates recruited to the program. “I witnessed her tremendous determination to develop independent research skills” and she “succeeded in all phases of the project, from design, data collection, data analysis and manuscript preparation.”
Among the 30 students who have entered the program since 2011, “Kristina is absolutely the standout in terms of motivation and enthusiasm for research,” Rosenheim said. “She leaped at the opportunity to learn how to become an independent researcher. Kristina will generate the first-lead authored publication for any student in our program—hopefully, the first of many. In this sense, she has already been a trailblazer for our program.”
Seybold noted that Tatiossian “worked on the host-finding behavior of a major pest of walnut trees, the walnut twig beetle. This is a nationally significant pest that spreads a disease of live trees called thousand cankers disease (TCD). The condition threatens not only the English walnuts that form the basis of the California nut industry, but also the black walnuts that represent over $500 billion in growing stock value of fine wood products in the eastern U.S.
“Kristina formulated her research project in fall 2011 and spring 2012 and then carried it out in spring and summer 2012. As she developed the project, she also applied to the Department of Entomology for a McBeth Scholarship, which she was awarded in summer 2012. The award helped her offset the costs of her research supplies and funded her travel to several scientific meetings.”
“Kristina collected a live population of the walnut twig beetle from a traditional orchard habitat in the southern Central Valley, reared the insects to the adult stage, and re-introduced the adults into freshly cut black walnut branch sections. Once the male beetles had begun producing their aggregation pheromones (attractants) in the branch sections, Kristina used the branch sections as lures to attract new males and females into flight traps. Using this basic technique she was able to establish that as few as 1 to 5 male beetles would provide a threshold of flight behavioral attraction in the field. This finding has ramifications for establishing an integrated pest management program for the walnut twig beetle nationwide.”
Tatiossian developed and displayed her poster at the 60th Annual Meeting of the Entomological Society (ESA), held Nov. 11-14, 2012 in Knoxville, Tenn. “Her poster reached a very interested target audience because Knoxville is in the heart of the distribution of eastern black walnut trees and in the center of the current distribution of TCD in the eastern U.S.,” Seybold said. “In a very creative touch, Kristina sculpted a replica of the female walnut twig beetle (through her participation in the UC Davis Art/Science Fusion Program) and attached the sculpture directly to her poster. This elicited quite a response at the national meeting and led to a news story released by UC Davis.”
The poster also drew attention at the arts exhibit at the 24th Annual UC Davis Undergraduate Research, Scholarship and Creative Activities Conference, held April 26, 2013.
In addition, Tatiossian delivered an oral presentation on her research at the 97th Annual Meeting of the Pacific Branch of the ESA in South Lake Tahoe, Nev.
Her poster, now on permanent display at Briggs Hall, credits Seybold; Extension entomologist Mary Louise Flint, associate director for Urban and Community IPM, UC Statewide Integrated Pest Program; entomology graduate student Stacy Hishinuma, and postdoctoral researcher Yigen Chen of the UC Davis Department of Entomology. Robin Schmidt of UC Davis Molecular and Cellular Biology mounted the unusual poster with the ceramic beetle.
This is part of the Forest Biology Research Center's Seminar Series coordinated by David Neale (email@example.com). David Rizzo is the host for the Seybold seminar.
A chemical ecologist specializing in forest insects, Seybold has studied the chemical ecology and behavior of bark beetles and related wood-boring insects for nearly 30 years and has published more than 150 peer-reviewed scientific papers, book chapters, and technical and outreach reports on the topic.
Seybold holds a bachelor of science degree in forest resources from the University of Wisconsin-Madison and a doctorate in entomology from UC Berkeley. His main interests include host selection and chemically mediated behaviors of bark beetles in conifers and hardwoods, as well as the behavior and biology of subsequent wood-degrading insects. Project areas range from molecular biology of pheromone production to the activity and detection of pheromones at the landscape level and the evolution of chemical communication systems of forest insects.
Seybold's research projects focus on the application of pheromones and other semiochemicals to forest management and to the detection of invasive species. He led a research effort that provided the first direct evidence for de novo biosynthesis of pheromones in bark beetles and continues to remain interested in the relationship between host biochemistry and insect metabolism in pheromone biosynthesis, which resulted in publications in the Proceedings of the National Academy of Sciences USA and the Annual Review of Entomology.