Project Number: 8042-32000-012-18-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Mar 1, 2019
End Date: Sep 30, 2021
The objectives of the proposed research are to (1) evaluate the oral, topical, and contact toxicity of novel experimental chemical compounds, including a pyrazole oxime and novel insect-selective carbamates against four major tick species of medical and veterinary importance; (2) to investigate the mode of action of those compounds by examining the behavioral and physiological responses of ticks as a result of exposure to those compounds at lethal and sub-lethal concentrations.
Three newly synthesized test compounds (PRC 408, 421, and 747) will be provided by the cooperator. Adult ticks (Amblyomma americanum, Ixodes scapularis, dermacentor variabilis, and Rhipicephalus sanguneus) will be obtained from a commercial source. (1) Toxicity bioassays. Topical treatment of ticks with test compounds will be done by using a Hamilton repeating dispenser A volume of 0.5 µl of test solution will be applied, and acetone alone treatment will serve as the negative control. Surface contact assay will be performed by treating glass scintillation vials (20 mL) with a test pesticide solution in acetone. Mortality will be determined 24-h post-treatment. Oral toxicity of test compounds will be determined using a capillary feeding method. Ticks will be immobilized using double-sided tape. Five-microliter glass capillary tubes will be filled with Shen’s Tick Saline containing the test compound. Each capillary tube will be inserted over a tick’s hypostome and palps and the tick will be allowed to feed for 6 hr. In vivo screening (topical, surface, and oral) signs of intoxication will be noted as this may be related to the potential modes of action that will be examined further in mode of action study. (2) Mode of action studies. Cholinesterase inhibition of a test compound will be measured using the Ellman Assay and compared to a carbamate standard (propoxur). In vitro cholinesterase inhibition data will be correlated with in vivo toxicity data. Impacts of those test compounds on tick feeding physiology will be examined by the combined use of capillary feeding and an electric feeding monitor. A silver wire will be glued to the dorsum of an immobilized tick; a second silver electrode will be inserted to that capillary tube containing the test compound dissolved in Shen’s Tick Saline fitted to the mouth parts of an adult tick. This setup will create a circuit that will allow recording of changes in feeding activities (blood sucking and salivation) of the tick as a result of pesticide action.