- Author: Kathy Keatley Garvey
Thanks to the generosity of his family, his work is continuing through memorial research grants to outstanding graduate students at the University of California, Davis.
Hazeltine, a native of San Jose, was a U.S. Navy veteran who studied entomology at UC Berkeley and received his doctorate in entomology from Purdue University in 1962. He managed the Butte County Mosquito Abatement District, Oroville, from 1966 to 1992, and the Lake County Mosquito Abatement District from 1961-1964.
He was an ardent supporter of the judicious use of public health pesticides to protect public health, remembers Bruce Eldridge, emeritus professor of entomology at UC Davis and former director of the (now folded) statewide UC Mosquito Research Program. Eldridge eulogized him at the 2005 annual meeting of the American Mosquito Control Association (AMCA) as "a man who made a difference." The AMCA journal published his eulogy in its 2006 edition. (See http://entomology.ucdavis.edu/files/154217.pdf)
"Bill was a medical entomologist who had a varied career in the field of mosquito biology and control, but he will forever be remembered as a man who fought in the trenches of the pesticide controversy from 1960 until the end of his life, and who made the safe and efficient use of pesticides in public health a personal crusade," Eldridge said.
In his memory, his three sons--Craig Hazeltine of Scottsdale, Ariz., Lee Hazeltine of Lincoln, formerly of Woodland, and the late Jeff Hazeltine (1958-2013)—established the UC Davis Bill Hazeltine Graduate Student Research Awards in 1997. Each year they travel to Davis to honor the recipients at a luncheon, timed with their attendance at a scholarship and fellowship celebration, hosted by Dean Helene Dillard, UC Davis College of Agricultural and Environmental Science.
The 2017 recipients are
- Olivia Winokur of the Christopher Barker lab, Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine. Her funded project ($2425): “Identifying Aedes Mosquito Eggs Using Hyperspectral Imaging: a Rapid, Low-Cost, Non-Destructive Method to Improve Mosquito Surveillance and Control.”
- Maribel "Mimi" Portilla of the Sharon Lawler lab, UC Davis Department of Entomology and Nematology. Her funded project ($2032): “The Management of Invasive Weeds and their Effects on Larval Culex mosquitoes."
Winokur is also the newly announced 2018 recipient of $3,094 to investigate Aedes aegypti immune response to Zika virus. (Portilla expects to receive her doctorate in six to 12 months.)
“Aedes aegypti and Aedes albopictus are mosquitoes capable of transmitting dengue, chikungunya, yellow fever, and Zika viruses,” Olivia Winokur explained in her 2017 application. “These species are invasive and present in California and continue to spread, increasing the likelihood of local transmission of these devastating viruses. Additionally, Aedes notoscriptus, an Australian mosquito whose vector competence for many viruses is unknown, has been detected in Los Angeles and is likely to spread in the state. Aedesmosquitoes are readily detected using ovitraps, a cheap and effective sampling method to detect the presence of gravid females. Ovitraps are especially useful when mosquito populations are low as traps for adult Aedes are unreliable. Once collected, the eggs cannot be differentiated using a stereomicroscope. Traditionally, identifying Aedes eggs collected in ovitraps requires hatching and rearing to adult for visual identification, which is time consuming and leads to a time lag for control, potentially allowing invasive species to spread without intervention.”
“Currently, I am developing a non-destructive, low-cost method to rapidly identify Aedes eggs,” Winokur wrote. “I have shown that species-specific surface morphologies of the exochorion can be used to differentiate species using electron microscopy. This method is expensive and therefore not a realistic surveillance technique. We can, however, exploit these species-specific surface morphologies in another way to identify Aedeseggs. Slight changes in morphological characteristics can be captured with high spatial resolution proximal sensing imaging, termed hyperspectral imaging.”
Winokur is testing “the use of hyperspectral imaging to differentiate between eggs collected from lab colonies of native and invasive Aedes mosquitoes in California. Preliminary data indicate this method shows promise for identifying species and warrants further testing. Once I have created species-specific reflectance profiles and validated my identification method using colony eggs, I will collect field eggs and validate the identification method using these field eggs.” She is working with hyperspectral imaging expert Christian Nansen, agricultural entomologist and assistant professor, UC Davis Department of Entomology and Nematology, on the project.
Winokur describes hyperspectral imaging as “a powerful tool that recognizes slight changes; therefore, we need to ensure that all samples are collected and conditioned the same way before testing. Samples must be imaged directly on the oviposition paper because exochorion cells are damaged by the ‘glue' the female uses to attach her eggs to the substrate; imaging removed eggs leads to inconsistent reflectance profiles. This method for rapidly identifying Aedes eggs will allow for quick response to the detection of invasive Aedes mosquitoes.”
After finishing her Ph.D., Winokur plans to remain in academia, but “I'm unsure exactly what that will look like! I really enjoy research, teaching, and mentoring so I'd like to have a career where I can do all of these. I also plan to have a career where I can conduct translational research with broad global health implications, engage non-scientists, create tools to help decision makers mitigate vector-borne disease burden worldwide, and encourage interest and diversity in STEM (science, technology, engineering and mathematics).”
Maribel "Mimi' Portilla
“At UC Berkeley School of Public Health, I was able to study health and disease within a larger context, and learned to consider the biological and the social determinants of disease. As I completed my degree, I realized I really missed the research experiences I had as an undergraduate. So, I looked for a way to bridge my new-found passion for public health and basic science research. This led me to UC Davis, where I learned about One Health and am now pursuing a Ph.D in medical entomology. Medical entomology is a perfect example of a One Health field, where I can seek out how interactions between humans and animals impact health. I am particularly interested in researching how disease risk may change as people manipulate the environment."
Her academic life revolves around writing her dissertation; teaching UC Davis classes (she's taught entomology, general biology and One Health classes); research; and public outreach. Since 2012, she has mentored some 30 undergraduate students on developing and executing their research experiments. She praised the “the diversity of my interns; they each brought such important and unique perspectives to the project.”
What are her career plans?
“Due to my diverse interests and skill set, I am very open about my career choices," Portilla said. "I have extensive teaching experience, and would love to be a professor with both teaching and research opportunities. However, there are many opportunities beyond academia. My research is introducing me to many other ways in which my work and research can help keep people safe and healthy. I hope to develop a strong research skill set while at UC Davis, and find a career path which takes advantage of my diverse abilities and love for One Health and Public Health."
Portilla mentioned pursuing a career as a teacher in a small liberal arts school to teach public health, general biology and global diseases classes, as well as do outreach and research. “I'm more of a scientist than an entomologist,” she said.
She may also pursue a career working in vector-control health education at the county, district or state level. “I'm open at this point,” Portilla said. Overall, she is geared toward improving public health outcomes through healthier environments. “I care about how outcomes affect the larger population,” she said.
Meanwhile, it's good to see that William Emery Hazeltine's passion for medical entomology lives on, and to see UC Davis graduate students benefit, all thanks to the generosity and thoughtfulness of the Hazeltine family. The "family" of 42 recipients since 1997 includes Christopher Barker, Winokur's major professor, who received a Hazeltine research award in 2006.
The complete list of recipients:
- 2018: Olivia Winokur (newly announced)
- 2017: Maribel "Mimi" Portilla and Olivia Winokur
- 2016: Sandy Olkowski, Maribel “Mimi” Portilla and Stephanie Kurniawan
- 2015: Sandy Olkowski, Maribel “Mimi” Portilla and Stephanie Kurniawan
- 2014: Martha Armijos, Elizabeth “Lizzy” Glennon and Rosanna Kwok
- 2013: Jenny Carlson, Elizabeth “Lizzy” Glennon and Sandy Olkowski
- 2012: Jenny Carlson, Kelly Liebman and Sandy Olkowski
- 2011: Brittany Nelms Mills, Kelly Liebman and Jenny Carlson
- 2010: Tara Thiemann and Jenny Carlson
- 2009: Kelly Liebman and Wei Xu
- 2008: Ashley Horton and Tara Thiemann
- 2007: Lisa Reimer and Jacklyn Wong
- 2006: Christopher Barker and Tania Morgan
- 2005: Nicole Mans
- 2004: Sharon Minnick
- 2003: Hannah Burrack
- 2002: Holly Ganz and Andradi Villalobos
- 2001: Laura Goddard and Linda Styer
- 2000: Laura Goddard
- 1999: Linda Boose Styer
- 1998: Larisa Vredevoe
- 1997: John Gimnig
- Author: Kathy Keatley Garvey
Seventeen-year-old Helena Leal doesn't like mosquitoes, but they like her.
“I always get bitten by mosquitoes more often than my family and friends,” says the Davis High School senior. “I get fairly bad reactions to mosquito bites, including swelling and itching, so I always have to be meticulous in using repellents.”
Thanks to her lifelong interest in those pesky female mosquitoes that target her for a free (blood) meal, Helena Leal now joins the ranks of published scientists. She's the lead author of UC Davis-based research published Dec. 21 in the journal Nature Scientific Reports.
“It was great to have the opportunity to do research addressing a question I've had ever since I was a child,” she said of the work, “Attraction of Culex Mosquitoes to Aldehydes from Human Emanations,” completed in the UC Davis Department of Molecular and Cellular Biology lab of her father, chemical ecologist Walter Leal. In addition to the father-daughter team, co-authors are UC Davis student researchers Justin K. Hwang and Kaiming Tan of the Leal lab.
Aldehydes are organic compounds—many fragrances are aldehydes—while skin emanations are odorants.
“Helena has always been curious about mosquito bites,” said her father, a distinguished professor who unravels the molecular mechanisms that make the olfactory system of insects so sensitive and selective. “Her research suggests that some people attract more mosquitoes—and receive more bites—because of their ratio of aldehydes, not because of natural repellents. We all produce these aldehydes but their ratios differ from person to person. The previous hypothesis is that people attract more mosquitoes because they lack a natural repellent. We found that the natural repellent is not produced in enough amount to repel.”
“Our paper shows that the aldehyde ratio is very important,” Helena said. The researchers studied the southern house mosquito, Culex quinquefasciatus. Female mosquitoes feed on humans and other vertebrates to acquire nutrients to develop their eggs, she noted. Infected mosquitoes can transmit such viruses as West Nile, Zika and the St. Louis encephalitis virus.
“The public has a genuine interest in understanding how mosquitoes find their hosts,” Helena wrote. “A Google search at the time of this writing, for example, produced almost 15 million results for the questions ‘why do mosquitoes find me?' Likewise, the question ‘why do mosquitoes prefer one person and not another?' generated more than 13 million results.”
An article in the July 13, 2013 edition of the Smithsonian magazine related that an estimated 20 percent of people “are especially delicious for mosquitoes and get bit more often on a consistent basis.”
Various factors contribute to differential attraction, including pregnancy, malaria infection, alcohol/beer consumption, skin microbiota, genetic makeup, and even blood type.
Fellow researcher Kaiming Tan said he was "delighted to see Helena able to facilitate her learning in a laboratory setting with a team of university students at UC Davis, a world-class research institution." He praised her interests in asking scientific questions, leading to solutions, as "useful skills in her future education endeavors."
"Dr. Leal's continuing support and mentoring on this student-run research project motivate us to pursue our goals," Tan added. "It is my pleasure to be on this team and pass down my knowledge to the next generation of college students."
Almost a century ago scientists identified carbon dioxide CO2 as a primary mosquito attractant, and it's commonly used to trap bloodseeking female mosquitoes. “However, no evidence is available that suggests that CO2 mediates differential attraction, i.e., carbon dioxide emission levels do not explain the common observation that mosquitoes systematically prefer one person to another,” the research team wrote. They agreed that skin emanations “play a key role in the mosquito finding a host” and that “these emanations are complex in nature and contain hundreds of compounds, but as far as mosquitoes are concerned, a handful of compounds activate the mosquito's olfactory system.”
“Anecdotes related to preferential mosquito bites are very common, but to date there is no complete explanation as to why one out of two people systematically receives more mosquito bites than the other when both are equally accessible,” the researchers wrote in their abstract. They tested the hypothesis that two constituents of skin emanations, 6-methyl-5-heptan-2-one (6MHO) and geranylacetone (GA), are natural repellents and may account for differential attraction in different ratios. “We studied skin emanations from two human subjects, confirmed in behavioral assays that female southern house mosquitoes are significantly more attracted to subject A (attractant) than to subject N (nonattractant), and tested their 6MHO/ GA ratios 2/23 in a dual-choice olfactometer.”
“Although repelling at high doses, 6MHO/GA mixtures were not active at the levels emitted by human skin,” they wrote. “We found, however, differential attraction elicited by the aldehydes in the ratios produced by subjects A and N. When tested in a dose commensurate with the level released from human skin and in the ratio produced by subject A, the aldehyde mixture significantly attracted mosquitoes. By contrast, an aldehyde mixture at the same ratio released by subject N did not attract mosquitoes. We, therefore, hypothesized that aldehydes may play a role in the commonly observed differential attraction.”
Helena worked on the project during the summer and into the fall. The Davis High School scholar recently received a scholarship from the Mexican-American Yolo County Concilio at its recognition dinner and scholarship fundraiser. She told the crowd that she plans to major in cognitive science with a focus on artificial intelligence.
Her other interests? "I play lacrosse and tennis on my school teams, but I also love to dance. I currently spend a lot of time working on the school yearbook as an editor. I am a big fan of live music and I am learning how to play the guitar."
Her brother, Gabriel, now 20, also did research in the Leal lab and saw his work on the odorant-binding protein of the yellow mosquito published. In addition, Gabriel worked on almond research (unpublished). Now a student at Dartmouth, Gabriel is majoring in economics and minoring in engineering and philosophy. Older brother Augusto, 26, holds a degree in political sciences from Princeton University with a minor in economics.
The Leal lab is “particularly interested in elucidating the roles of odorant-binding proteins, odorant receptors, and odorant-degrading enzymes,” said Leal, adding that “Insects are extremely successful animals whose lives intertwine with ours. They may be vegetarian and harmful to our food supply as well as vectors of pathogens that inflict tremendous suffering and human loses. Thus, a better understanding of the molecular basis of insect olfaction may facilitate the design of eco-friendly chemicals to controls insects of medical and agricultural importance.”
The Leal lab is credited with discovering the exact mode of action of DEET, “the gold standard” of insect repellents for the past six decades. “DEET doesn't mask the smell of the host or jam the insect's senses,” Leal said. “Mosquitoes don't like it because it smells bad to them. That's why they avoid it.” The also discovered the DEET receptor, which is also sensitive to plant defense compounds.
“It's interesting what will repel and what will attract mosquitoes,” said Helena Leal. “It appears that mosquitoes will always find me--and 20 percent of the rest of the population—as especially delicious. They're out for blood—our blood. Let's keep them at bay with repellents.”
(Editor's Note: Walter Leal is a fellow of the Entomological Society of America and former chair of the UC Davis Department of Entomology and Nematology.)