Community ecologist Louie Yang, professor, UC Davis Department of Entomology and Nematology (Photo by Kathy Keatley Garvey)

“This study collected a high-resolution temporal dataset on milkweed-monarch interactions during the last three years prior to the precipitous single-year population decline of western monarchs in 2018,” said community ecologist Louie Yang, a professor in the Department of Entomology and Nematology.

Yang organized and led a 135-member team, all co-authors of the paper, “Different Factors Limit Early- and Late-Season Windows of Opportunity for Monarch Development,” published in the journal  Ecology and Evolution. (This document is open access at https://bit.ly/3volFaI.)

From 2015 through 2017, the team monitored the interactions of monarchs,  Danaus plexippus, on narrow-leaved milkweed, Asclepias fascicularis, planted in December 2013on city-owned property adjacent to the North Davis irrigation channel. 

“This study has three key findings,” the UC Davis professor said. “First, we documented early and late seasonal windows of opportunity in the wild, migratory western monarch population. Second, our data suggest that early and late seasonal windows were constrained by different factors. Third, climatic and microclimatic variation had a strong effect on the timing and importance of multiple factors affecting monarch development. Broadly, we hope that this study contributes to a more temporally detailed understanding of the complex factors that contribute to year-to-year variation in monarch breeding success.” 

This monarch larva is newly hatched. (Photo by Larry Snyder)

Feared on its way to extinction, the migratory monarch is now on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species as Endangered—threatened by habitat destruction and climate change.  Statistics show that the overwintering population of western monarchs along coastal California has declined by more than 99 percent since the 1980s, according to the Xerces Society for Invertebrate Conservation.

The UC Davis-based team set out to answer three questions: (1) How do the developmental prospects of monarchs vary in time, within- and across years? (2) How do the combined effects of bottom-up, top-down, and abiotic factors interact with seasonal variation in monarch density to constrain the timing and extent of seasonal windows of opportunity? and (3) How do climatic variation and microhabitat heterogeneity affect these constraints?

A monarch chrysalis at the UC Davis research site. (Photo by Larry Snyder)

The results showed that different combinations of factors constrained the early- and late-season windows of opportunity for monarch recruitment.  “Early-season windows of opportunity were characterized by high egg densities and low survival on a select subset of host plants, consistent with the hypothesis that early-spring migrant female monarchs select earlier-emerging plants to balance a seasonal trade-off between increasing host plant quantity and decreasing host plant quality,” the abstract relates. “Late-season windows of opportunity were coincident with the initiation of host plant senescence, and caterpillar success was negatively correlated with heatwave exposure, consistent with the hypothesis that late-season windows were constrained by plant defense traits and thermal stress.” 

The researchers also noted: 

• “Throughout this study, climatic and microclimatic variations played a foundational role in the timing and success of monarch developmental windows by affecting bottom-up, top-down, and abiotic limitations. More exposed microclimates were associated with higher developmental success during cooler conditions, and more shaded microclimates were associated with higher developmental success during warmer conditions, suggesting that habitat heterogeneity could buffer the effects of climatic variation.”
• “Together, these findings show an important dimension of seasonal change in milkweed-monarch interactions and illustrate how different biotic and abiotic factors can limit the developmental success of monarchs across the breeding season. These results also suggest the potential for seasonal sequences of favorable or unfavorable conditions across the breeding range to strongly affect monarch population dynamics.”

Yang and his team planted 318 narrow-leaved milkweed adjacent to the seasonal irrigation channel, which carries runoff water with a “seasonal pattern of generally increased flow during summer irrigation periods and immediately following winter precipitation events. As a result, this site combines several elements representative of the California Central Valley at a landscape scale.”   The Davis site typifies a “Mediterranean pattern of cool, wet winters and hot dry summers.”

The researchers recorded daily temperatures and precipitation in one dataset, and in a second dataset, sub-hourly temperature observations, approximately every 20 minutes. They defined the “early season” as days 90–180 (approximately the end of March to the end of June) and the late season as days 180–270 (approximately the end of June to the end of September) each year.” 

They measured and recorded the milkweed growth and leaf area removal by herbivores, and counted and measured the eggs and larvae. They also gathered information on the predator and herbivore community. 

MMMILC Project. Participants in the Monitoring Milkweed–Monarch Interactions for Learning and Conservation (MMMILC) Project, directed by Yang, collected most of the observations. Yang provided hands-on, in-person training in milkweed-monarch biology, data collection, and data entry protocols, partnering with the Environmental Science internship program led by Eric Bastin at Davis Senior High School and the Growing Green internship program led by Karen Swan at the Center for Land-based Learning, Woodland.

 “We documented 674 weekly observations of monarch eggs and 997 weekly observations of monarch caterpillars across the three years of this study,” the researchers wrote. “Monarchs were most numerous in 2016. We observed 2.7 times as many monarch eggs in 2016 as in 2015 and 2.2 times as many as in 2017. We observed 3.0 times as many caterpillars in 2016 as in 2015, and 2.5 times as many as in 2017. Separated by year and normalized by the total number of emerged plants each year, we observed 137 eggs and 193 caterpillars (0.49 egg and 0.69 caterpillar observations per plant) in 2015, 369 eggs and 576 caterpillars (1.55 egg and 2.42 caterpillar observations per plant) in 2016 and 168 eggs and 226 caterpillars (0.74 egg and 1.0 caterpillar observations per plant) in 2017.

Among their research findings:

• The early and late monarch developmental periods were generally warmer in 2017 than in the two previous years.
• The number of surviving emerged plants declined over the 3-year study, from 281 (88.3 percent) in 2015, to 238 (75 percent) in 2016 to 226 (71 percent) in 2017. However, an increasing proportion of the surviving plants attained a total stem length exceeding 50 cm across these same years: 137 (49 percent of 281) in 2015, 144 (61 percent of 238) in 2016, and 175 (77 percent of 226).
• The growth of milkweeds changed dramatically in 2017 following the rainy winter of 2016–2017. Milkweeds in 2017 attained sizes (maximum weekly mean total stem lengths) that were 70 percent larger than in 2015, and 64 percent larger than in 2016, and the variance of the plant size distribution also increased.
• Milkweed emerged earliest in 2016 (mean emergence day 110) and nearly four weeks later in 2017 (mean emergence day 137).

Unfortunately, a City of Davis maintenance crew unintentionally mowed the site on May 5, 2017, “damaging several plants in this population. However, most plants in the population were below the height of the mower blades at this point in the growing season.”  

Today the milkweed population at the North Davis Channel is being maintained by the City of Davis and dedicated citizens, including Larry Snyder, who documented the project in photographs. “We aren't monitoring there intensively, but we've seen monarch eggs, caterpillars and adults there this year,” Yang said. 

More monarch projects from the Louie Yang lab are pending. “The next paper in press represents research done several years ago and is focused on the timing of herbivory and its effects on flowering,” he said.  “We are studying several California milkweed species.” 

Graduate student Mia Lippey

"In summary, I aim to use ecoinformatics (ecological big data, aggregated from multiple sources) to examine the impact of global change on agricultural insect populations," Lippey related. "A consistent challenge for researchers working in natural and managed ecosystems is that data available for characterizing insect responses to global change are severely limited across space and time. As a result, we know very little about how insects are responding to global change over time, and to what extent various global change drivers (e.g., climate change, land use change, pesticides) are responsible for documented changes in insect abundance. Here, I will use long-term data collected in agricultural systems for other purposes to bridge this data gap."

"Because field scouts and farmers collect data in a decentralized way, the availability, size, and accuracy of relevant agricultural data are unrivaled," she noted. "This approach will contribute to the emergence of a novel framework using big data to investigate global change questions across larger spatial and temporal axes than ever before. My results will have implications for the impact of anthropogenic pressure on food production stability, biodiversity, and ecosystem health."

Lippey, who received her bachelor's degree in entomology from UC Davis in 2019, is a graduate student of agricultural entomology in the Rosenheim lab, and an urban entomology graduate student in the Meineke lab. She previously did research in the Louie Yang lab, 2018-2021, as an undergraduate research assistant in insect ecology, and as an undergraduate research assistant in ant systematics with the Philip Ward lab.

In the Yang lab, Lippey investigated the effect of stripes on aversive behavior in fruit flies (Drosophila melanogaster), tsetse flies (Glossina), and mosquitoes (Aedes); studied the effect of size and movement constraints on ontogenetic color change (OCC) of swallowtail larvae (Papilio); and co-authored a collaborative review paper,  "The Complexity of Global Change and its Effects on Insects," published in 2021 in the Current Opinion in Insect Science.

In the Ward lab, she studied the phenotypic evolution of the Big-Eyed Tree Ant (Pseudomyrmecinae: Tetraponera) and delivered a presentation on the project at the 2019 UC Davis Undergraduate Research Conference.

Lippey presented a poster on "Effects of Surrounding Landscapes on the Fork-tailed Bush Katydid (Scudderia furcata) in California Citrus" at the 2021 Entomological Society of America conference in Denver.

A talented illustrator, Lippey served as an illustrator and author of BuprestidID, an apolyclave identification key for more than 500 genera of Buprestidae (family of beetles known as jewel beetles or metallic wood-boring beetles) in a project headed by USDA's Animal and Plant Health Inspection Service.

Two UC Davis Department of Entomology and Nematology faculty members are now full professors, and a third faculty member has achieved tenure as associate professor. 

Molecular geneticist and physiologist Joanna Chiu, vice chair of the department, and community ecologist Louie Yang were promoted from associate professors to professors, effective July 1.  Community ecologist Rachel Vannette was promoted from assistant professor to associate professor. 

Professor Joanna Chiu

Chiu's research expertise includes molecular genetics of biological timing and posttranslational regulation of proteins. She uses animal models including Drosophila melanogaster and mice to study the mechanisms that regulate circadian and seasonal physiology and behavior.  Major grants from the National Institutes of Health and the National Science Foundation fund her biological rhythms research. In addition to her research in biological rhythms, Chiu also aims to leverage her expertise in genomics to address key issues in global food security. 

In 2019, she was named one of 10 UC Davis Chancellor's Fellows, an honor awarded to associate professors who excel in research and teaching. 

Chiu and Yang co-founded and co-direct (with Professor Jay Rosenheim) the campuswide Research Scholars Program in Insect Biology, launched in 2011 to provide undergraduates with a closely mentored research experience in biology. The program crosses numerous biological fields, including population biology; behavior and ecology; biodiversity and evolutionary ecology; agroecology; genetics and molecular biology; biochemistry and physiology; entomology; and cell biology. The goal is to provide academically strong and highly motivated undergraduates with a multi-year research experience that cultivates skills that will prepare them for a career in biological research. 

Professor Louie Yang

Yang won the 2018 Outstanding Faculty Academic Advising Award from NACADA, also known as the  Global Community for Academic Advising; and the 2017 Faculty Advisor Award of Excellence in NACADA's Pacific Region 9, comprised of California, Nevada and Hawaii. 

Yang says of the research underway in his lab:  “We study how species interactions change over time. We apply a diversity of approaches and perspectives to a diversity of systems and questions. We do experimental community ecology. We also use observational methods, meta-analysis, conceptual synthesis, ecosystem perspectives, and theoretical models. We like data, and we like learning new things.”

Associate Professor Rachel Vannette

Vannette received her bachelor of science degree, summa cum laude, in 2006 from Calvin College, Grand Rapids,Mich., and her doctorate from the University of Michigan's Department of Ecology and Evolutionary Biology, Ann Arbor, in 2011. She received a Hellman Fellowship grant in 2018 and a National Science Foundation Faculty Early Career Development Award in 2019 to study microbial communities in flowers and a National Science Foundation grant to support work on solitary bee microbiomes.

Of her research, Vannette says: “ All plants are colonized by microorganisms that influence plant traits and interactions with other species, including insects that consume or pollinate plants. I am interested in the basic and applied aspects of microbial contributions to the interaction between plants and insects. I also use these systems to answer basic ecological questions, such as what mechanisms influence plant biodiversity and trait evolution.” 

“The Vannette lab is a team of entomologists, microbiologists, chemical ecologists, and community ecologists trying to understand how microbial communities affect plants and insects (sometimes other organisms, too),” she says. “We often study microbial communities in flowers, on insects or in soil. We rely on natural history observations, and use techniques from chemical ecology, microbial ecology and community ecology.  In some cases, we study applied problems  with an immediate application including pathogen control or how to support pollinators. Other questions may not have an immediate application but are nonetheless grounded in theory and will contribute to basic knowledge and conservation (e.g. how can dispersal differences among organisms affect patterns of abundance or biodiversity?)”

Forest entomologist Jackson Audley is expected to receive his doctorate in December 2019. (Photo by Kathy Keatley Garvey)

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.”