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.
“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. demolitoroffspring 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.”
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.”
And those soybean loopers? Those major pests of soybeans? Thanks to this research, we now know more about physiological responses to parasitism--and there's more to come. (We're also admiring the amazing photography of Jena Johnson!)
As the researchers said: "The hyperspectral proximal imaging technologies represent an important frontier in insect physiology."
If you've been following the innovative work of agricultural entomologist and remote sensing technology researcher Christian Nansen, associate professor of entomology at the University of California, Davis, you can.
Using Skittles (candy), magnolia leaves, mosquito eggs and sheets of paper, 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.
He 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!”
“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.”
“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.
They can also do something else.
Basically, 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, according to UC Davis agricultural entomologist Christian Nansen of the Department of Entomology and Nematology.
In groundbreaking research published in the journal Plant Methods, Nansen 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).”
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."
Both Karban and Nansen contributed chapters to the recently published book, The Language of Plants (University of Minnesota Press). The book explores "the idea that plants can think, feel, and communicate as a way of reconfiguring our relationship with the natural world," according to editors Monica Gagliano, John C. Ryan, and Patrícia Vieira.
"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," Nansen said. "She 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.
In his paper, titled “Edge-Biased Distributions of Insects: A Review,” Nguyen reviewed how many species of insects show a definite preference for living on the edges of fields and orchards.
This phenomenon can lead to more accurate monitoring and better pest management tactics, said Nguyen and co-author Nansen.
The paper indicates that “the prevalence of such edge-biased distributions has considerable implications for how to sample and monitor insects, and it also suggests that in many cases pest management tactics, such as, releases of natural enemies or insecticide applications can be spatially targeted to field edges.”
Nguyen traced the history of edge-based distribution of insects in agricultural systems to a study on black bean aphids led by British entomologist C. G. Johnson and published in 1950 in the Annual of Applied Biology. The aphids, major pests of sugar beet, bean and celery crops, spread from the field edges to within, but the edges remained the areas of highest aphid density.
Nguyen also called attention to scientific studies that found that wild bees in high bush blueberry were more prevalent along the edges of orchards, and that the density of the pest, Asian citrus psyllid, prevailed more at the edges of citrus groves than within.
Nansen praised Nguyen's work as outstanding. “Sometimes we professors are fortunate enough to interact with undergraduate students who – even with English not being their first language – possess keen abilities to describe a scientific problem or phenomenon in clearly articulated scientific writing, and Derrick is a great example of that!”
“He started writing drafts of this review article about six months before he started as a graduate student,” Nansen said. "This review article is an example of how we can use writing of review papers as a tool to engage with undergraduate students before they start their thesis projects.” Professor Jay Rosenheim of the UC Davis Department of Entomology and Nematology also helped with the drafts.
“We are supposed to focus more and more on ‘diversity' and here we have an undergraduate from Singapore publishing in a very prestigious journal,” Nansen added.
The UC Davis scientists suggest that mathematical modeling approaches can partially explain edge-biased distributions but “that abiotic factors, crop vegetation traits, and environmental parameters are factors that are likely responsible for this phenomenon.”
They advocate more research, especially experimental research, “to increase the current understanding of how and why edge-biased distributions of insects are so widespread.”
“In my opinion, discussions about edge-biased distribution of insects tend to be entomocentric; much emphasis is often put on the insects themselves,” Nguyen commented. “However, agricultural insect pests are dependent on their host plants for survival. Interestingly, it has been shown in various systems that agricultural crops also display edge effect as well. Therefore, through my review, I would like to bring attention to this correlation and propose insect-plant interactions as a potential explanation of edge effect and broaden the discussion about this widely observed but insufficiently understood phenomenon.”
Nguyen received a bachelor's degree in plant sciences from UC Davis in December 2017, graduating with highest honors. A high-achieving scholar, he was on the dean's honor list, College of Agricultural and Environmental Sciences, every quarter since the fall of 2015. He enrolled in the UC Davis graduate student program in entomology in January 2018.
“I am interested in IPM, insect behavior and insect ecology, and greenhouse production of leafy vegetables,” he said. “Currently I am working on projects that explore the potentials of hyperspectral imaging technology as early detection tools for pest infestation and insect host selection based on the framework of preference-performance hypothesis. As my research model, I focus on the interactions between vegetables (bok choy and spinach) and their insect pests (leafminers and armyworms).
Nguyen served as an assistant training officer with the Singapore Armed Forces (SAF) from April 2014 to March 2015. For his studies at UC Davis, he received a 2015-2019 undergraduate and graduate scholarship sponsored by Agri-Food and Veterinary Authority of Singapore.
“For my career plan, since I am currently sponsored by AVA, I will be working for them for six years upon my graduation,” Nguyen said. “In the long term, I am interested in doing a Ph.D in imaging technology for pest detection, plant health status analysis and food quality analysis.”
And if you attended the UC Davis Bohart Museum of Entomology open house on Dec. 5, 2015, you may have seen entomology student Wade Spencer showing visitors the larvae devouring his Styrofoam bicycle helmet.
And if you've been following the news from Environmental Protection Agency (EPA), you may have heard about the UC Davis doctoral student who just received a $15,000 grant in EPA's National Student Design Competition for Sustainability Focusing on People Prosperity and the Planet (P3).
That would be Trevor Fowles, a second-year doctoral student in the UC Davis Department of Entomology and Nematology, who submitted his research project, “Beetle Larvae as Biodegraders of Styrofoam and Organic Waste.” He now has an opportunity to score a $75,000 grant in Phase 2 of the competition. He'll be in Washington DC April 7-8 for the National Sustainable Design Expo at the Science and Engineering Festival.
Meanwhile, his 100,000 mealworms in the Briggs Hall lab of his major professor Christian Nansen, are munching up a storm (well, a blizzard of the white stuff) in a project that Fowles hopes will make a difference in breaking down Styrofoam--especially a problem in the nation's landfills--and offer sustainable environmental solutions.
“It's about insects processing waste,” Fowles said of his research. “In three weeks they ate three-fourths of a pound of styrofoam, converting it into biodegradable waste.”
“Trevor's project should be viewed as an example of what entomological agricultural research is all about in the 21st Century--developing new and highly innovative ways to recycle resources and more sustainable food production systems," said agricultural entomologist Christian Nansen, an associate professor of entomology who specializes in applied insect ecology, integrated pest management (IPM) and remote sensing. In addition, the project has an applied evolutionary angle, which Fowles intends to explore.
"Our plan is to selectively breed insects and their microbial gut biome, so that they become highly adapted to breakdown, not only Styrofoam, but also different kinds of agricultural waste products," Nansen said. "Similar to orchard growers bringing in bee hives during flowering periods for pollination, we envision that, in the future, companies will be able to order strains of insects for biodegradation of specific wastes. That is, the future of applied entomology will in different ways be about identifying and developing ways for insects to provide different societal services, including pollination, biological control, and biodegradation."
The UC Davis research project involves designing a pilot-scale styrofoam biodegradation unit to take in regional Styrofoam and organic waste, and establish a high-performance beetle lineage, or the “best beetle larvae to do the job.” The adult beetles also eat Styrofoam, but not as much.
“Organization of our food systems will be a defining challenge in the upcoming century and I believe insects will play a significant role in transforming our agricultural sectors,” Fowles said.
The design emphasizes economic feasibility, community engagement, and environmental stewardship. To be sustainable, the project is aimed at connecting local community stakeholders with research expertise to produce an ecofriendly alternative for Styrofoam disposal.
After biodegrading the Styrofoam, the beetles can be pelletized for animal feed, Fowles said, and the excrement or frass can be used as “high-value amendment to compost mixtures.” He figures that that since Styrofoam by itself is a poor nutrient source for the beetle larvae, he eventually will mix it with organic waste materials, such as, pulp from wine and tomato industries, to optimize beetle development.
The darkling beetles and larvae are pests of stored grains, but the larvae are widely used throughout the world as food for humans; for captive pets, including fish, reptiles and birds; and as fish bait. They are reared commercially on fresh oats, wheat bran or grain, and often with sliced potato, carrots, or apple as a moisture source.
In the wild, darkling beetles and larvae are general decomposers, eating decaying leaves, sticks, grasses, and carcasses.
Fowles said he received his first colony of mealworms in 2016 from then graduate student Tom Nguyen at the Bohart Museum of Entomology (Nguyen is now a researcher at the Smithsonian Institution). Fowles purchased his 100,000 mealworms from the insect farm, Rainbow Mealworms and Crickets in Compton.
Fowles, who grew up in West Sacramento, received his bachelor's degree in biology in 2011 from San Diego State University. Before entering the UC Davis graduate student program, he served as a lab manager for five years for Carroll/Loye Biological Research, launched by the UC Davis entomological team of Scott Carroll and Jenella Loye.
In a news release, EPA Administrator Scott Pruitt said: “This year's P3 teams are applying their classroom learning to create valuable, cutting-edge technologies. This next generation of scientists is designing sustainable solutions that will help protect public health and the environment and ensure America continues to lead the world in innovation and science for decades to come.”
Fowles obtained his first colony of mealworms in 2016 from then graduate student Tom Nguyen at the Bohart Museum of Entomology, now a researcher at the Smithsonian Institution. Fowles purchased his 100,000 mealworms from the insect farm, Rainbow Mealworms and Crickets in Compton.
The project in the Christian Nansen lab is all good news for the environment. Who would have thought that beetle larvae would chow down on Styrofoam, the stuff that fills our landfills and what holds our coffee and take-out orders?
Stanford researchers say that every year we Americans throw away 2.5 billion plastic foam cups alone. And that's just a fraction of the 33 million tons of plastic that Americans discard every year. Another statistic: less than 10 percent of that total gets recycled. And as a Stanford news release indicated "the remainder presents challenges ranging from water contamination to animal poisoning."
Bring on the high-performance UC Davis beetles!