- Author: Kathy Keatley Garvey
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.
- Author: Kathy Keatley Garvey
But non-healthy insects, just like sick humans, can also show changes in body reflectance.
Newly published research led by a University of California, Davis agricultural entomologist shows that radiometric energy reflected by pesticide-exposed adult beetles indicates when they become “terminally ill.”
Christian Nansen, lead author of “Detection of Temporal Changes in Insect Body Reflectance in Responses to Killing Agents,” published in PLOS ONE, said the first-of-its-kind research is “completely non-destructive and completely non-invasive.”
“The results may be of considerable relevance to insect physiologists and toxicologists studying responses to treatments and/or to behavioral entomologists studying adaptations and behavioral responses,” he said.
Nansen and colleagues Leandro Prado Ribeiro of the University of São Paulo,Brazil, and Ian Dadour and John Dale Roberts of the University of Western Australia researched the effects of two species of beetles exposed to killing agents (an insecticidal plant extract and entomopathogenic nematodes).
Their subjects were maize weevils (Sitophilus zeamais), and larger black flour beetles (Cynaus angustus). The maize weevil is a major pest of corn and also feeds on standing crops and stored cereal products, including wheat, rice, sorghum, oats, barley, rye, buckwheat, peas and cottonseed, as well as pasta.
“The larger black flour beetle thrives in cotton gin trash piles on the Southern High Plains of Texas,” Nansen said, “and sometimes becomes a nuisance after invading public and private structures.”
In their study, they addressed two questions: 1) Will exposure to known killing agents cause a detectable change in body reflectance? And 2) And if so, after what exposure time?
“It is common to use infra-red thermometers to measure skin reflectance of radiometric energy in specific wavelengths as part of determining our body temperature, and body temperature is one of the key diagnostics in detection of human illnesses,” said Nansen, a specialist in integrated pest management (IPM), insect ecology and remote sensing. “In our study, we analyzed radiometric energy reflection by adult beetles (in particular wavelengths in the visible and infra-red spectrum) and showed that reflectance features change when beetles are starting to become terminally ill!”
“By following their body reflectance over time, we demonstrated that, compared to healthy /untreated individuals, there was a significant change in the body reflectance at the time point when killing agents are known to cause lethal symptoms.”
“Specific spectral bands were used to develop reflectance-based classification models for each species, and independent validation of classification algorithms showed sensitivity (ability to positively detect terminal stress in beetles) and specificity (ability to positively detect healthy beetles) of about 90 percent,” the authors wrote. “Significant changes in body reflectance occurred at exposure times, which coincided with published exposure times and known physiological responses to each killing agent. The results from this study underscore the potential of hyperspectral imaging as an approach to non-destructively and non-invasively quantify stress detection in insects and other animals.”
Nansen, a native of Denmark, received his master's degree in biology from the University of Copenhagen in 1995 and his doctorate in zoology from the Royal Veterinary and Agricultural University in Denmark in 2000. He accepted positions in Portugal, Benin, United States, UK and Australia before joining the UC Davis Department of Entomology and Nematology in January as an assistant professor. His international experience also includes being an international exchange student at the University of Lisbon, Portugal and a visiting professor at Northwest A&F University, Yangling, China. As part of his undergraduate studies, Nansen traveled to Brazil to write a book about sustainable agriculture in rainforest areas.