When a wasp lays its eggs inside a caterpillar or parasitizes it, it's not always easy to tell what's going on without destroying both species.

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 scientists studied two common parasitic wasps or parasitoids, Microplitis demolitor, and Copidosoma floridanum, which lay their eggs in the larval stages of the soybean looper moth, Chrysodeixis includens. The pest, found throughout much of North and South America and elsewhere, feeds on soybeans.

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.

The researchers said that the accuracy rate of more than 85 percent holds promise. “The hyperspectral proximal imaging technologies represent an important frontier in insect physiology, as these technologies can be used non-invasively to characterize physiological response across a range of time scale factors, such as minutes of exposure or acclimation to abiotic factors, circadian rhythms, and seasonal effects. Although this study is based on data from a host-parasitoid system, results may be of broad relevance to insect physiologists.”

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.”

DAVIS--Using candy (Skittles), magnolia leaves, mosquito eggs and sheets of paper, UC Davis agricultural entomologist and remote sensing technology researcher Christian Nansen explored how light penetrates and scatters--and found that how you see an object can depend on what is next to it, under it or behind it.

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.

Doctoral candidate Emily Bick of the Christian Nansen lab, UC Davis Department of Entomology and Nematology, is the recipient of the Entomological Society of America's 2018 student certification award, which recognizes outstanding entomology students interested in the mission of the ESA certification program.

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.

What does the does the student certification award entail? “Post college, I sat for and passed the ESA Board Certified Entomologist exam," she said. "Then, this past summer, I was flown to Denver, Co., by the Centers for Disease Control and Prevention (CDC) to sit for the Medical Entomology Specialty Exam. At that time, I sat for an additional exam--Plant-Related Entomology Specialty. The Student Certification Award is given to a student who is a Board-Certified Entomologist who has written an essay about the importance of the Board Certification process."

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.

If you're a plant and an insect is attacking you, you can communicate your stress to nearby plants as a way to alert them about potential danger--very similar to how animals communicate or respond to predators.

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.