2013 Annual Report
1a.Objectives (from AD-416):
To devise innovative methods for the suppression of insects that transmit diseases to U.S. military deployed abroad.
1b.Approach (from AD-416):
Identify and test compounds with insecticidal activity that makes them especially
beneficial in the rapid control of mosquitoes, flies, and other arthopods responsible for carrying disease agent. Devise innovative means of applying control agents especially suited for use in combat or deployment conditions. Identify and test new classes of topical and area repellents for use by troops.
A patent was filed for a chromene derivative with longer duration of repellent activity than the commercial repellent DEET against multiple species of mosquitoes. In our fatty acid structure-activity relationship studies, the focus for 2012 was on the evaluation of fatty acid chain length and degree of unsaturation. The focus for 2013 was on synthetic derivatives of fatty acids. Esterifications and acylations were performed on those compounds identified as most active from previous studies, namely undecanoic, dodecanoic, undecenoic, and dodecenoic acids. Due to the low cost of the starting materials undecanoic and dodecanoic acids, synthetic modification began on these compounds and also included methylations of all saturated fatty acids. Evaluations for mosquito repellency were performed on the first series of esters synthesized from dodecanoic acid. In all instances the activity decreased relative to the starting material dodecanoic acid.
The investigation of the Native American insect repelling folk remedy, sweetgrass (Hierochloe odorata), is nearing completion. One bioactive compound has been isolated and identified and a second compound is currently undergoing structure elucidation studies.
Adult Mosquito Insecticide Discovery:
ARS scientists have identified a highly active mosquito adulticide that behaves like pyrethrin from a plant material. In addition, a fungal metabolite has been isolated and identified as an adulticide against mosquitoes. The analogs of this compound are being synthesized for further testing.
Mosquito Larvacide Discovery:
Cardol and cardanol derivatives have been isolated and identified as mosquito larvicides. Lastly, Angelica dahuria essential oil and ethanol extracts showed strong mosquito larvicidal activity. Further studies of Angelica species are planned.