But newly published research by UC Davis agricultural entomologist Christian Nansen and insect physiologist Michael Strand of the University of Georgia reveals a new, non-destructive and quite accurate method to characterize physiological responses to parasitism: proximal remote sensing or body reflectance response data.
They published their research, “Proximal Remote Sensing to Non-Destructive Detect and Diagnose Physiological Response by Host Insect Larvae to Parasitism,” Dec. 4 in the journal Frontiers in Physiology.
Nansen, first author of the paper and an associate professor in the UC Davis Department of Entomology and Nematology, specializes in insect ecology, integrated pest management and remote sensing. Strand, a professor of entomology at the University of Georgia, is an international authority on the physiology of insect parasitism.
The Nansen-Strand project involved soybean loopers without parasitism (control group) and with parasitism, involving both wasp species.
“Based on reflectance data acquired three to five days post-parasitism, all three treatments (control larvae, and those parasitized by either M. demolitor or C. floridanum) could be classified with more than 85 percent accuracy,” they wrote.
Due to parasitism-induced inhibition of growth, “it's easy to differentiate soybean loopers parasitized by M. demolitor from non-parasitized larvae as long as the developmental stage of the host larva is known,” they said. In addition, a single M. demolitor offspring emerges from the host larva 7-9 days post-parasitism to pupate, while non-parasitized larvae continue to increase in size to the final instar.
Copidosoma floridanum minimally alters host growth until late in the final instar, when thousands of wasp progeny complete their development. This wasp is known for having the largest recorded brood—3,055 individuals--of any parasitoidal insect.
Parasitoids are often categorized as either idiobionts--whose hosts cease development after parasitism--or koinobionts--whose hosts continue to develop as the parasitoids offspring grow. “Parasitoids also are commonly divided into ectoparasitic species whose offspring grow by feeding externally on hosts or endoparsitoids, whose offspring grow by feeding internally,” the authors wrote. “Most known idiobionts are either ectoparasitoids that paralyze and lay eggs on the surface of larval stage hosts or are endoparasitoids that lay their eggs inside sessile host stages like eggs or pupae.”
Both of the wasps they studied are idiobionts and endoparasitoids.
Nansen noted that “many species of minute wasps are parasitoids of eggs and larvae of other insects, and parasitism represents one of the most extreme life strategies among animals”
“Living inside the body of another animal,” he said, “poses a series of non-trivial challenges, including how to overcome/suppress the defense response by the host; how to obtain oxygen; how to feed on the host without killing it--because once the host is dead, then microbial organisms and general decomposition will make the host body unsuitable--and how to manage waste.”
Nansen likened the developing parasitoids to astronauts flying in a space capsule. “A developing parasitoid faces a long list of serious practical challenges, so the evolutionary selection pressure has been immense and lead to some of the most extreme cases of co-evolution.”
Nansen, an associate professor in the UC Davis Department of Entomology and Nematology, published his observations in a recent edition of PLOS ONE, the Public Library of Science's peer-reviewed, open-access journal. He researches the discipline of remote sensing technology, which he describes as “crucial to studying insect behavior and physiology, as well as management of agricultural systems.”
Nansen demonstrated that several factors greatly influence the reflectance data acquired from an object. “The reflected energy from an object--how it looks-- is a complex cocktail of energy being scattered off the object's surface in many directions and of energy penetrating into the object before being reflected,” Nansen pointed out. “Because of scattering of light, the appearance--or more accurately the reflectance profile--of an object depends on what is next to it! And because of penetration, the appearance of an object may also be influenced by what is behind it!”
“We don't think of us humans having x-ray vision, but part of what we see is actually reflectance from layers/tissues below the surface,” Nansen related. “Like the fairy tale about how a true princess can feel a pea underneath many mattresses, penetration of light affects what we consider surface reflectance. This is easily demonstrated by placing a white sheet of paper on top of a paper with colored dots--even with a few sheets of white paper on top of the dots, it is still possible to see the colored dots--so some level of penetration is detectable by the human eye. But advanced cameras are much more sensitive to penetration than the human eye.”
Biomedical researchers “take great advantage of penetration--the ability of radiometric energy to penetrate into soft human tissues, such as the brain, liver, lung, skin--to characterize the function or structure of tissues as part of disease diagnosis and image-guided surgery,” Nansen said. “But in non-medical classifications of objects, penetration and scattering represent a challenge, because these optical phenomena can lead to unexpected ‘noise' in the reflectance data and therefore reduced performance of reflectance based classifications of objects.”
“The findings are of considerable relevance to research into development of remote sensing technologies, machine vision, and/or optical sorting systems as tools to classify/distinguish insects, seeds, plants, pharmaceutical products, and food items.”
In the PLOS ONE article, titled “Penetration and Scattering—Two Optical Phenomena to Consider When Applying Proximal Remote Sensing Technologies to Object Classifications,” Nansen defines proximal remote sensing as “acquisition and classification of reflectance or transmittance signals with an imaging sensor mounted within a short distance (under 1m and typically much less) from target objects.”
In recent years, Nansen has shown that reflectance profiling of objects can be used to differentiate viable and non-viable seeds; insects expressing terminal stress imposed by killing agents; developmental stages of fly pupae; and insect species in a cryptic complex.
“Even though the objects may look very similar--that is, indistinguishable--to the human eye, there are minute/subtle differences in reflectance in some spectral bands, “ Nansen said, “and these differences can be detected and used to classify objects.”
With this newly published study, Nansen has demonstrated experimentally that imaging conditions need to be carefully controlled and standardized. Otherwise, he said, “penetration and scattering can negatively affect the quality of reflectance data, and therefore, the potential of remote sensing technologies, machine vision, and/or optical sorting systems as tools to classify objects. “
Nansen described the rapidly growing number of studies describing applications of proximal remote sensing as “largely driven by the technology becoming progressively more robust, cost-effective, and also user-friendly.”
“The latter,” he wrote, “means that scientists who come from a wide range of academic backgrounds become involved in applied proximal remote sensing applications without necessarily having the theoretical knowledge to appreciate the complexity and importance of phenomena associated with optical physics; the author of this article falls squarely in that category!”
“Sometimes experimental research unravels limitations and challenges associated with the methods or technologies we use and thought we were so-called experts on,” Nansen commented.
Nansen, who specializes in insect ecology, integrated pest management, and remote sensing, joined the UC Davis faculty in 2014 after holding faculty positions at Texas A&M, Texas Tech and most recently, the University of Western Australia.
Bick is one of 19 recipients of this year's ESA's Professional and Student Awards, which recognize scientists, educators, and students who have distinguished themselves through their contributions to entomology.
The awardees will be honored at “Entomology 2018,” the joint meeting of the entomological societies of America, Canada and British Columbia, to take place Nov. 11-14 in Vancouver, B.C.
Bick focuses her career on leveraging entomological knowledge to best serve people. Her career includes working in industry to develop practical solutions for invasion biology of urban forests. For her master's degree, she researched an invasive aquatic weed, the water hyacinth, and its insect biological control agent, Neochetina bruchi.
For her doctorate, she is behaviorally manipulating a pesticide-resistant insect (Lygus spp.) away from high-value horticultural crops using a push-pull strategy. “I use simulation models of ecosystems to optimize integrated pest management strategies, a technique I learned while on an American Scandinavian Foundation Fellowship working with Dr. Niels Holst out of Aarhus University in Denmark,” she said.
A native of New York City, Bick received her bachelor's degree in entomology from Cornell University, Ithaca, N.Y., and her master's degree in entomology from UC Davis. She is a Board-Certified Entomologist, specializing in medical and plant entomology.
Bick credits a high school research program with inspiring her to study entomology. “I was in a high school science research program and chose to work on an insect repellent because I did not like mosquitoes,” Bick said. “Four years later, I was majoring in entomology at Cornell.”
The UC Davis doctoral student was a member of the 2016 UC Davis Linnaean Games Team that won the ESA national championship for expertise in answering questions about insects and entomologists. Now she has an opportunity to win another national championship: she is a member of the 2018 UC Berkeley-UC Davis Linnaean Games Team that will compete for national honors at the November ESA meeting. Ralph Washington Jr., a graduate student at UC Berkeley and a former graduate student at UC Davis, captains the team, which also is comprised of Brendon Boudinot, Zachary Griebenow and Jill Oberski, all of the Phil Ward lab.
Bick recently drew praise for her review of the San Francisco Playhouse production, "An Entomologist's Love Story," published in the ESA blog, Entomology Today.
The 7000-member ESA, founded in 1889 and headquartered in Annapolis, Md., is the world's largest organization serving the professional and scientific needs of entomologists and people in related disciplines. Its members are affiliated educational institutions, health agencies, private industry, and government.
In groundbreaking research published in the journal Plant Methods, UC Davis agricultural entomologist Christian Nansen of the Department of Entomology and Nematology and his team of six colleagues from Brazil discovered that plant-plant communication causes physiological changes in plants and these subtle changes can be detected via analyses of leaf reflectance or hyperspectral imaging. The article is titled “Hyperspectral Imaging to Characterize Plant-Plant Communication in Response to Insect Herbivory."
The growing knowledge about plant-plant communication and about plants' ability to assess their environment has led to concepts like “plant neuro-biology” and “plant behavior,” said Nansen, an associate professor who centers his research on host plant-stress detection, host selection by arthropods, pesticide performance, and use of reflectance-based imaging in a wide range of research applications.
“We know that plants don't have a neural system or brain,” said Nansen, “but respected scientists are studying plants as if they did, as if plants are able to assess conditions in their environments, and they can adapt/respond to those conditions.”
“In studies of plant stress signaling, a major challenge is the lack of non-invasive methods to detect physiological plant responses and to characterize plant-plant communication over time and space.” Nansen pointed out. He described the research as “initial evidence of how hyperspectral imaging may be considered a powerful non-invasive method to increase our current understanding of both direct plant responses to biotic stressors but also to the multiple ways plant communities are able to communicate.”
The UC Davis entomologist and his team used leaf reflectance data to detect and characterize plant responses to stressors, knowing that induced stress interferes with photosynthesis, chemical composition and physical structure of the plant, thus affecting the absorption of light energy and altering the reflectance spectrum of the plants.
“For several decades, it has been known that plants communicate – both among individuals of the same species and across species,” Nansen related. “That is, volatiles emitted by one plant can be received by another plant and trigger different physiological responses. It is also well-documented that plants communicate via roots, and sometimes the roots from different plants are brought together in a network of communication and exchange of nutrients through symbioses with mychorriza (soil fungi).”
Nansen credited Professor Richard Karban of the Department of Entomology and Nematology with pioneering efforts in the field of plant-plant communication, and lauded his continuing research. Plants can eavesdrop, sense danger in the environment, and can distinguish friend from foe, says Karban, the author of the landmark book, “Plant Sensing and Communication” (University of Chicago Press). In addition, both Nansen and Karban contributed chapters to the recently published book, “The Language of Plants” (University of Minnesota Press).
Of the Nansen study, Karban said: "This study describes a technique that may provide a relatively quick and inexpensive way to evaluate levels of resistance in plants. If these results are repeatable by other workers in other systems, they will provide a very valuable tool for researchers and growers."
Nansen noted that within "the last decade or so, extremely cutting-edge research in the field of plant-plant communication has been done by people like Dr. Monica Gagliano of the University of Western Australia. "Gagliano has elegantly demonstrated that plants can respond not only to aerial volatile compounds and root secretions but also to sound."
For the research project, Nansen and his team decided to conduct “a very simple experiment with corn plants and stink bugs.” They planted corn plants in separate pots or two in one pot. They subjected some plants to herbivory by stink bugs, while other plants served as control plants.
The scientists collected two types of data: phytocompounds (stress hormones and pigments) and leaf reflectance data (proximal remote sensing data).
“Our research hypothesis was that insect herbivory causes changes in leaf phytocompound levels, and these physiological defense responses are associated with detectable changes in phytocompound levels and in certain spectral bands of leaf reflectance profiles,” Nansen pointed out. As a secondary hypothesis, the researchers predicted that plant-plant communication (from plant with herbivory to an adjacent control plant without herbivory) will elicit both a change in phytocompound composition of leaves and also cause a corresponding change in leaf reflectance.
The result: The first published study, in which comprehensive phytocompound data have been shown to correlate with leaf reflectance. In addition, it is the first published study of leaf reflectance in plant-plant communication.
Nansen and co-author Leandro do Prado Ribeiro of the Research Center for Family Agriculture, Research and Rural Extension Company of Santa Catarina, Brazil, conceived and designed the experiments. The Brazilian National Counsel of Technological and Scientific Development provided partial financial support. Co-author Marilia Almeida Trapp received financial support from a Capes-Humboldt Research Fellowship.
Both are seeking a doctorate at the University of California, Davis. They differ in that Winokur focuses her research primarily on the yellow-fever mosquito, Aedes aegypti, while Portilla's research involves Culex mosquitoes, which transmit West Nile virus and other diseases.
They are alike in that they share the passion of the late William Emery Hazeltine (1926-1994), who worked tirelessly in mosquito research and public health.
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, awarding the first one 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.
Winokur's funded project: “Identifying Aedes Mosquito Eggs Using Hyperspectral Imaging: a Rapid, Low-Cost, Non-Destructive Method to Improve Mosquito Surveillance and Control.”
Portilla's project: “The Management of Invasive Weeds and their Effects on Larval Culex mosquitoes.”
“Aedes aegypti and Aedes albopictus are mosquitoes capable of transmitting dengue, chikungunya, yellow fever, and Zika viruses,” Winokur explained in her 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.”
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.”
Winokur is using the 2017 Hazeltine funds to improve identification of invasive Aedes mosquito eggs in California and to attend the 2017 American Society of Tropical Medicine and Hygiene conference. She is also the newly announced recipient of a 2018 Hazeltine Student Research Award for $3,094, this time to investigate Aedes aegypti immune response to Zika virus.
A native of Long Beach, Calif., Olivia grew up in Laguna Niguel, Calif., where she focused on science at the Dana Hills High School Health and Medical Occupations Academy. She received her bachelor's degree in 2015 from Cornell University, majoring in Interdisciplinary Studies and focusing on the environmental effects on human health. She enrolled in the UC Davis graduate program in 2016 as a Ph.D entomology student with a designated emphasis in the biology of vector-borne diseases. Earlier this year, Winokur received a three-year National Science Foundation Graduate Research Fellowship.
Maribel Portilla, currently writing her dissertation, said the three chapters will encompass: the management practices of the invasive exotic weeds, Brazilian waterweed (Egeria densa) and water hyacinth (Eichhornia crassipes), in the Sacramento-San Joaquin Delta and how those practices impact mosquitoes and their habitat; herbicide use in managing those weeds and how herbicides affects the larval habitat; and the direct effects of herbicides on larval mosquito development.
Her goal: “to inform and create better techniques to reduce both mosquito and weed problems."
Like Winokur, Portilla is grateful for the Hazeltine research funds. “I am currently exploring some molecular/genetic techniques (PCR and sequencing) to identify the species of mosquitoes I collected in the different weed/habitat mesocosms, This will be funded by the Hazeltine award I received.”
Portilla, who calls the South Bay home (San Martin, Santa Clara County), holds a master's degree in public health from UC Berkeley, where “I was able to study health and disease within a larger context, and learned to consider the biological and the social determinants of disease.” Her area of expertise incorporates her love for biology and her strong interest in social issues.
“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. 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.
Portilla may also pursue a career working in vector-control health education at the county, district or state level. “I'm open at this point,” she said. Overall, she is geared toward improving public health outcomes through healthier environments. “I care about how outcomes affect the larger population,” she said.
“Bill Hazeltine was an advocate for the use of mosquito control to protect people from mosquitoes and the disease agents they transmit, and he believed chemical control to be a necessary part of the means to accomplish this,” wrote Eldridge, who valued his friendship. “He also considered himself an environmentalist, and billed himself as such on his business cards and on his signature block. He had a vast knowledge of pesticides and pesticide legislation, and a strong belief in the scientific basis for public policy issues related to the safe and effective use of pesticides. Because the federal Endangered Species Act influenced mosquito control, he became an authority on this as well."
“After Bill's death, I was contacted by his sons about the possibility of establishing a William Hazeltine Memorial Scholarship Fund at UC Davis,” Eldridge noted. “They believed this would represent an important contribution because of Bill's strong interest and support of medical entomology research, and because of Bill's admiration of UC programs in mosquito control. The fund has grown to the point where graduate student awards can now be funded just from the interest, and a number of students at UCD have benefited from the thoughtfulness of the Hazeltine family.”
The 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