- Author: Kathy Keatley Garvey
Yes, it does, says UC Davis agricultural entomologist Christian Nansen of the Department of Entomology and Nematology, who set out to investigate whether there's a relationship between the “physiological” and “behavioral” resistance in insects and found “some quite interesting patterns.”
In a first-of-its-kind research, published March 4 in the Public Library of Science (PLOS), Nansen and his colleagues discovered that “certainly there was an effect of level of physiological resistance or susceptibility of moth strains” – this they demonstrated by comparing two moth strains with high and low levels of insecticide resistance. But they also found intriguing differences in life stages. “We found that ovipositing females and developing larvae may not show the same levels of behavioral responses to insecticides.”
“This is all very interesting and clearly links theoretical evolutionary biology with applied pest management,” he said, concluding that “behavioral avoidance ought to be considered in evaluating the performance of an insecticide.”
The research, “Behavioral Avoidance—Will Physiological Insecticide Resistance Level of Insect Strains Affect their Oviposition and Movement Responses,” by Christian Nansen and fellow scientists Maria Nansen of UC Davis and Olivier Baissac, Kevin Powis and Greg Baker, all of Australia, targeted the Brassica pest, Plutella xylostella, commonly known as “the cabbage moth.” It is responsible for an estimated $4 to $5 billion loss annually in the United States, Nansen said. Cole crops are the moth's host plant. It lays its eggs only on the family Brassicaceae. Its larvae or caterpillars feed on the leaves, floral stalks and flower buds.
The main objective of the Christian Nansen-led study was to quantify two possible types of behavioral avoidance:
- under choice conditions with leaves having different levels of pesticide spray coverage (including an untreated control leaf), females oviposit predominantly on leaf surfaces without insecticides, and
- larvae avoiding insecticide-treated leaf surfaces.
“As a model system, we studied movement and oviposition responses by two strains of DBM denoted ‘single resistance' and ‘double resistance' based on their levels of physiological resistance to two insecticides: gamma-cyhalothrin and spinetoram,” they wrote.
The researchers compared behavioral responses by these two strains as part of characterizing the relative effect of levels of physiological resistance on the likelihood of insects showing signs of behavioral avoidance.
“Although we are unaware of any theoretical framework providing clear predictions of expected behavioral responses by phenotypes with different of physiological resistance," Nansen said, "we predicted that: (1) DBM individuals with confirmed physiological resistance to a given combination of dosage and insecticide show similar movement and oviposition responses to host plant surfaces with/without insecticides, and (2) DBM individuals should avoid insecticide treated surfaces and show significant changes in movement and oviposition behavior, if they are exposed to a combination of dosage and insecticide to which they are susceptible.”
Nansen said the study “highlights the possibility of associations between physiological resistance and avoidance responses by ovipositing females. In addition, larvae from the single resistance strain moved significant faster than those from the double resistance strain, when the entire arena was treated with either gamma-cyhalothrin or spinetoram.”
"Our study highlights the importance of conducting behavioral studies as part of characterizing effects of selective pressures by insecticides and as part of performance evaluations of insecticides.”
The diamondback moth, thought to be of European origin, is found throughout the Americas and in Europe, Asia, Africa, Australia, New Zealand and the Hawaiian Islands. It was first observed in North America in 1854 in Illinois and by 1883 had spread to Florida and the Rocky Mountains, data shows.
The diamondback moth was the first insect found to have become resistant to biological control by the Bt toxin (from Bacillus thuringiensis) in the field. In the 1980s, the moth developed resistance to pyrethroids, and today, virtually all insecticides are ineffective, entomologists say.
Cold winters help to kill off overwintering pests. In California, natural enemies can often effectively control the diamondback moth, according to the UC Integrated Pest Management (UC IPM) Program website. “In southern California, the ichneumonid wasp, Diadegma insularis, has been identified as the most common parasite. Trichogramma pretiosum may also attack diamondback eggs," IPM says. "Various predators such as ground beetles, true bugs, syrphid fly larvae, and spiders can be important factors in controlling populations.”
- Author: Kathy Keatley Garvey
The review, co-authored by Nansen and Norman Elliott of the U.S. Department of Food and Agriculture's Agricultural Research Service, Stillwater, Okla., explains remote sensing and highlights how it influences entomological research by “enabling scientists to nondestructively monitor how individual insects respond to treatments and ambient conditions. Furthermore, novel remote sensing technologies are creating intriguing interdisciplinary bridges between entomology and disciplines such as informatics and electrical engineering.”
“To most people, remote sensing refers to imaging-and reflectance-based surveying mounted on airborne devices and vehicles such as airplanes or satellites,” they pointed out. They rely on a broader definition: “The measurement or acquisition of information of some property of an object or phenomenon by a recording device that is not in physical or intimate contact with the object or phenomenon under study.”
“Consequently, even imaging through a microscope may be considered a type of remote sensing,” they wrote. “In many remote sensing applications, the data are collected in parts of the radiometric spectrum that are not detectable by the human eye…We wish to emphasize that entomological remote sensing is expanding in many directions and creating intriguing opportunities for collaborative research between entomology and disciplines such as informatics and electrical engineering. “
Remote sensing has been an established research discipline for more than four decades, Nansen related. “It was Isaac Newton who discovered that light could be separated into a spectrum of colors, and approximately 100 years later, James Clerk Maxwell discovered that light as we see it is part of a very wide radiometric spectrum.”
(See the Nansen/Elliott review at http://www.annualreviews.org/doi/abs/10.1146/annurev-ento-010715-023834)
The Annual Review of Entomology, launched in 1956, reviews significant developments in the field of entomology, including biochemistry and physiology, morphology and development, behavior and neuroscience, ecology, agricultural entomology and pest management, biological control, forest entomology, acarines and other arthropods, medical and veterinary entomology, pathology, vectors of plant disease, genetics, genomics, and systematics, evolution, and biogeography.
Nansen, who joined the UC Davis Department of Entomology and Nematology in 2015, is focusing on four major themes: host plant stress detection, host selection by arthropods, pesticide performance, and use of reflectance-based imaging in a wide range of research applications.
He is using his international expertise to zero in on more sustainable farming systems, better food production and fewer pesticides.
“The agricultural sector in California is so exciting, because of its diversity and economic importance,” said Nansen, whose agricultural entomology expertise encompasses seven countries including his native Denmark. “Secondly, there is a strong spirit of innovation in this region, and I hope to contribute to the development of highly advanced crop monitoring systems and decision support tools, so that farming practices can become less reliant on pesticides.”
Born and educated in Denmark, Nansen 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. Nansen previously held faculty positions at Texas A&M, Texas Tech, and most recently at the University of Western Australia.
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.
Related Link:
Christian Nansen's Website
- 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.
- Author: Kathy Keatley Garvey
A team of scientists, including Christian Nansen, agricultural entomologist at the University of California, Davis, answered those questions in their research, “How Do ‘Mute' Cicadas Produce their Calling Songs?” in the Feb. 25th edition of PLOS ONE, an open access peer-reviewed scientific journal published by the Public Library of Science.
Cicadas in the genus Karenia lack the specialized sound-producing structures that characterize most cicadas, according to Nansen and colleagues Changquing Luo and Cong Wei, both of Northwest A&F University, China.
Although they don't possess the tymbal mechanism, the word “mute,” is misleading, says Nansen, assistant professor in the UC Davis Department of Entomology and Nematology. “They do indeed produce sounds.”
The researchers discovered a new sound-production mechanism in Karenia caelatata, which produces impact sounds by banging the forewing costa against the operculum. It's somewhat like beating a drum while other cicada species with tymbal mechanisms play an orchestra of diverse and loud sounds.
In their publication, the researchers described the temporal, frequency and amplitude of the sound produced.
“Morphological studies and reflectance-based analyses reveal that the structures involved in sound production of K. caelatata(i.e., forewing, operculum, cruciform elevation, and wing-holding groove on scutellum) are all morphologically modified,” they wrote. “Acoustic playback experiments and behavioral observations suggest that the impact sounds of K. caelatataare used in intraspecific communication and function as calling songs.”
“The new sound-production mechanism expands our knowledge on the diversity of acoustic signaling behavior in cicadas and further underscores the need for more bioacoustic studies on cicadas which lack tymbal mechanism,” they concluded in their abstract.
Cicadas, also known as “tree crickets” (from Latin cicada), are among the most widely recognized of insects due to their large size, usually 2 to 5 centimeters or more, and loud sounds, sometime as high as 120 decibels. Theirs is among the loudest of all insect-produced sounds. Cicadas live in warm climates, from temperate to tropical. Immature cicadas spend most of their lives sucking juice from tree roots. The adults suck plant juices from stems.
The best-known North American genus, Magicicada, has a long life cycle of 13 or 17 years and emerges in great numbers.
Cicadas damage cultivated crops, shrubs, and trees, mainly from females scarring tree branches where they lay their eggs. In many cultures, cicadas are a delicacy on the menu.
Links:
PLOS Research:
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0118554
PLOS Research YouTube:
https://www.youtube.com/watch?v=AVC8ZSaOydY
Christian Nansen Website:
http://chrnansen.wix.com/nansen2
Science News:
https://www.sciencenews.org/blog/science-ticker/some-cicadas-drum-beat-help-their-wings
All About Cicadas
http://www.biokids.umich.edu/critters/Cicadidae/
- Author: Kathy Keatley Garvey
“The agricultural sector in California is so exciting, because of its diversity and economic importance,” said Nansen, whose agricultural entomology expertise encompasses seven countries including his native Denmark. “Secondly, there is a strong spirit of innovation in this region, and I hope to contribute to the development of highly advanced crop monitoring systems and decision support tools, so that farming practices can become less reliant on pesticides.”
“I also believe that the strong academic programs at UC Davis with ecology and evolution are of incredible value, and that we can integrate the basic theory from these disciplines into the fundamental of crop management to obtain more sustainable farming systems,” Nansen said. “As an example of a line of research I am interested in – application of fertilizers obviously affect crop growth, but they also affect the attractiveness of crops to many insect pests, and they influence the ability of plants to resist attacks by several important insect pests.”
“So, how can we optimize use of crop fertilizers to stimulate yields but also minimize risks of pest infestations? The answer to such a question is underpinned by in-depth understanding about host selection ecology and about fitness and evolutionary processes involved in host adaptation. In other words, it is critically important to demonstrate how we can use studies of agricultural systems to learn about the ecology of species and their food webs and evolutionary processes.”
At UC Davis, Nansen is focusing on four major themes: host plant stress detection, host selection by arthropods, pesticide performance, and use of reflectance-based imaging in a wide range of research applications.
As part of his undergraduate studies, Nansen took time off to travel to Brazil to write a book about sustainable agriculture in rainforest areas. “In this process, I learned about the potential of honey bees as both pollinators of crops but also as ‘promoters' more broadly of sustainable agricultural development,” Nansen said.
Nansen wrote his master's thesis on honey bees: “The Apis mellifera Forging Response to the Pollen Availability in Cistus salvifolius.” The plant isalso known as a sage-leaved rock rose or Gallipoli rose. He conducted field work in Portugal involving pollen identification, observations on daily flight and foraging activity, and modeling of pollen availability.
For his doctorate, his interest turned to the larger grain borer, a serious pest of stored maize and dried cassava roots. He wrote his dissertation on “The Spatial Distribution and Potential Hosts of the Larger Grain Borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae), in a forest in Benin, West Africa.” His research involved stored product insect ecology, field trapping with pheromone traps, experimental work on pheromone production, vegetation analysis, satellite image interpretation, laboratory infestation of potential breeding substrates, and histological studies.
“Agricultural entomology has given me so many opportunities to travel and work internationally, and that has been extremely rewarding,” he said. “I am passionate about food production and how to produce food ‘smartly' – so that it is profitable and also environmentally sustainable. And insects are critically important in manipulated food webs, such as, a crop field, forest, orchard, or horticultural greenhouse. I enjoy studying their ecological roles in these systems and how we can use that information to develop smarter ways to produce food.”
Nansen recalled that his childhood exposures to international scientists played a major role in his choice of a career. His father, a professor in veterinary parasitology, entertained many colleagues in the family home. “And my mother cooked the food! This is probably the main reasons why I enjoy both cooking and why my career has been so international.”
“Even though Denmark is a very small country (5 million people),” Nansen said, “it has been at the forefront of agricultural research and production for many decades. And growing up, my father took me on field trips and exposed me to farming systems.” In fact, young Christian earned his weekly allowance in the chicken business: he sold eggs to neighbors.
Nansen said he is delighted to see a “steadily growing appreciation for the origin and quality of the food we eat. Today, in the 21st century, the technologies deployed in modern agriculture are so advanced and similar to the cutting-edge technologies in other fields, he said. “Those technologies require skill sets beyond what most people may be aware of. Use of drones, remote sensing, GIS models, mathematical models of weather, crop physiology and soil dynamics, models to optimize input requirements and minimize economic risks, phone apps to optimize applications of agro-chemicals – these are all skill sets and approaches we are using as part of studying food production systems and developing innovative and reliable tools to be used within the agricultural sector.”
Nansen previously held faculty positions at Texas A&M, Texas Tech, and most recently at the University of Western Australia. As a university employee, the most common way to “create impact” is by influencing the minds and interests of students, but also of particular stakeholders,” he said.
“While working in Texas, we developed a very effective sampling method for an important insect pest in potato fields, and a 4th generation potato grower (Bruce Barrett) actually changed his management strategy because of our sampling method: he purchased the equipment needed and hired people specifically to conduct insect sampling, as he saw how use of this method could save him thousands of dollars on insecticide sprays--because he would now have a much better idea about when and where to spray. Recently, in Australia we demonstrated to farmers that sub-optimal maintenance of their stored seed grain led to loss of crop vigor and therefore a loss in crop yields. That is, if the seed grain is poorly managed, then stored grain infestations will likely occur, and these beetles will damage the kernels so they don't germinate. We provided simple guidelines for how the grain storage practices could be improved, so quite a few farmers are now following our guidelines to optimize the vigor of their seed grain.”
“Sometimes, we can go further and actually develop tools or gadgets which end-users may find useful. As an example, we have developed a freely available phone app to optimize pesticide spray applications based on weather and spray settings (http://agspsrap31.agric.wa.gov.au/snapcard/). The main goal with this phone app is to guide farmers so that they obtain the best possible spray coverage--to reduce risk of pests developing resistance--and to encourage them NOT to spray pesticides under unfavorable conditions.”
