Location: Invasive Insect Biocontrol & Behavior Laboratory
2015 Annual Report
Objectives
Objective 1: Design and synthesize novel chemicals such as toxicants, repellents, and attractants that can be used to mitigate the impact of blood-feeding arthropods.
Objective 2: Determine physiological and molecular mechanisms involved in the detection of attractants, repellents, and feeding deterrents by mosquitoes in order to facilitate discovery of novel behavior-modifying chemicals.
Sub-objective 2.A: Characterize gustatory receptors (GRs) and other chemosensory genes in the major gustatory appendages of Aedes aegypti, localize their expression and relative abundance, and determine their function through heterologous expression studies.
Sub-objective 2.B: Determine the specificity of gustatory receptor neurons (GRNs) expressing identified GRs with emphasis on detection of feeding stimulants and repellents, and their role in Ae. aegypti feeding and avoidance behavior.
Objective 3: Develop improved surveillance and control techniques for bed bugs.
Sub-objective 3.A: Identify and elucidate the role of chemicals involved in the behaviors of dispersal (repellency) and aggregation (attractancy), and develop new detection techniques.
Sub-objective 3.B: Develop new chemical or biological control agents to reduce or eliminate bed bug infestations.
Objective 4: Discover and develop new tools for the control of ticks affecting humans, and evaluate their effectiveness at a range of conditions associated with climate change.
Sub-objective 4.A: Develop new tick repellents/formulations and characterize the physiological mechanisms involved in repellent detection by ticks.
Sub-objective 4.B: Determine if certain abiotic and biotic factors affect the responses of deer ticks to repellents.
Approach
New toxicants, repellents and attractants will be synthesized using quantitative structure-activity relationship analyses. This component will also focus on the development of novel inhibitors of detoxifying enzymes that are found in insects. Candidate compounds obtained from existing chemical libraries and commercial sources will be screened for bioactivity against blood-sucking arthropods.
Gustatory receptors and genes in the appendages of the yellow fever mosquito Aedes aegypti will be characterized. Molecular studies will also determine the specificity of gustatory receptor neurons with emphasis on feeding stimulants and repellents.
Chemicals that attract and repel bed bugs will be identified, and their role elucidated. To develop new monitoring devices, behavioral studies will use a photographic tracking system to monitor bed bug responses to behavior-altering compounds. New chemical and biological control agents will also be developed under this objective to mitigate the impact of this blood-sucking pest.
New tick repellents and formulations will be developed and the mechanism of repellent detection by ticks characterized. This will involve the optimization of an in vitro feeding system for ticks, as well as the use of electrophysiological techniques to characterize tick responses to repellents and antifeedants. The effect of pathogen infection status, temperature, humidity, and geographic origin of ticks will also be investigated with regard to repellents.
Progress Report
In mosquito control research, ARS scientists concluded dose-response relationships of fast acting pyrethroids that were developed on suitable matrices to enhance vapor pressure at ambient temperature. World Health Organization (WHO) protocol for bottle assays were followed and used to evaluate adult mosquito knockdown efficacy. For pesticide resistance management, novel commercially viable CYP-450 inhibitors of natural product origin were identified, and two commercial partners in the public health pesticide industry have initiated trials to determine efficacy and economical viability. A provisional patent application was filed for novel CYP-450 inhibitors as insecticide adjuvant.
In translational mosquito research, ARS scientists showed that sensory nerve cells located on the mouthparts of a mosquito capable of transmitting malaria in the eastern United States, could actually detect repellents such as DEET. Repellents not only stimulated specific sensory cells, but also decreased the activity of cells normally responsive to feeding stimulants like sugar. Knowledge of the nerve mechanisms by which these important disease vectors detect repellents present a better understanding of the senses involved in initiating mosquito feeding behavior and provide targets for development of chemicals aimed at disrupting mosquito feeding. ARS scientists used gene editing to construct mutant mosquitoes lacking individual receptor genes thought be involved in sensing attractants and repellents. These mutant mosquitoes will be useful in determining the role of individual genes in attraction and feeding behavior.
In bed bug research, ARS scientists showed that a fungus that targets insects is not particularly suitable for bed bugs. Bed bugs exposed to this fungus by various methods, only showed high mortality when the relative humidity was 98%. At lower humidities, mortality was unacceptable. In research involving bed bug behavior, ARS scientist demonstrated that bed bug defensive secretions could either repel or attract bed bugs, depending on the concentration of the chemicals. At high concentrations, the two major compounds that comprise the defensive secretions repelled bed bugs, while at lower concentrations they appeared attractive to the bed bugs. This information will be useful to industry personnel that are attempting to design effective lures and monitors for detecting bed bugs.
Using immature stages of the deer tick and the lone star tick, sixty two essential oil natural products were evaluated for their repellent activity using a vertical paper bioassay technique. Dose-repellency relationships were compared to DEET, a commercially-available repellent. Five natural products were equally effective as DEET, while two test compounds were shown to be more effective than DEET. These natural products will be further evaluated in various combinations and mixture formulations with DEET in the second year to study synergism among different chemicals for new tick repellent products with enhanced efficacy. Laboratory research is also in progress to determine how temperature and humidity conditions affect ticks’ response to DEET, which will eventually lead to field studies.
Accomplishments
Review Publications
Dickens, J.C., Bohbot, J.D. 2015. Neuromolecular basis of repellent action. Insect Repellents Handbook. 2nd edition. New York, NY: CRC Press Taylor & Francis Group. p.31-42.
Ulrich, K.R., Feldlaufer, M.F., St. Leger, R.J., Thorne, B.L. 2014. Exposure of bed bugs to metarhizium anisopliae, and the effect of defensive secretions on fungal growth in vitro. Journal of Economic Entomology. 107(6):2190-2195.
Renthal, R., Li, A.Y., Gao, X., Perez De Leon, A.A. 2014. Polar cuticular lipids differ in male and female sandflies (Phlebotomus papatasi). Comparative Biochemistry and Physiology. 51(6):1237-1241.
Sparks, J.T., Dickens, J.C. 2014. Physiological recordings and RNA sequencing of the gustatory appendages of the yellow-fever mosquito Aedes aegypti. Journal of Visualized Experiments. p.94 DOI:10.3791/52088.
Kim, J., Roh, M.S., Dickens, J.C., Lee, A., Suh, J. 2014. Volatiles emitted from single flower buds of the lilium longiflorum × L. callosum interspecific hybrid and its parents. Journal of Horticulture, Environment and Biotechnology. 55(5):410-414.
Sparks, J.T., Bohbot, J.D., Dickens, J.C. 2015. Olfactory disruption: towards controlling important insect vectors of disease. Progress in Molecular Biology and Translational Science. New York, NY: Elsevier Academic Press. p. 81-108.
Zheng, H., Li, A.Y., Teel, P.D., Perez De Leon, A.A., Seshu, J., Liu, J. 2015. Biological and physiological characterization of in vitro blood feeding in the nymphal and adult stages of Ornithodoros turicata (Acari: Argasidae). Journal of Insect Physiology. 75(4):73-79.
Dickens, J.C., Bohbot, J.D., Sparks, J.T. 2015. Multiple chemosensory targets for discovery of novel chemicals for disruption of mosquito behavior. Antenna. 39:90-91.
Ulrich, K.R., Feldlaufer, M.F., Kramer, M.H., St. Leger, R.J. 2015. Inhibition of the entomopathogenic fungus Metarhizium anisopliae in vitro by the bed bug defensive secretions (E)-2-hexenal and (E)-2-octenal. Biocontrol. Doi: 10.1007/s10526-015-9667-2.
Perez De Leon, A.A., Teel, P.D., Li, A.Y., Ponnusamy, L., Roe, M. 2014. Advancing integrated tick management to mitigate burden of tick-borne diseases. Outlooks on Pest Management. 25(6):382-389.
Khanna, H., Chauhan, K.R. 2014. Biobased Lactams as Novel Arthropod Repellents. Natural Product Communications. 9:1671-1672.
Chauhan, K.R., Bernier, U.R. 2014. In silico models for development of insect repellents. In: Strickman, D., Francis, editors. Insect Repellents Handbook. 2nd edition. Boca Raton, FL: CRC Press. p. 53-72.
