Repellency of synthetic and plant-derived preparations for Culicoides imicola.

The study was conducted to find a safer and longer lasting repellent for C.imicola than di-ethyl toluamide (DEET), to validate whether the current recommendations in Israel for application of repellents during an outbreak of disease caused by pathogens borne by Culicoides imicola are justified, and to test plant-derived preparations as potential replacements for the synthetic repellents. Seven repellents were compared by a method using treated netting across the entrance of a suction light trap. Those inferior to DEET were: oregano and Herbipet which showed a slight non-significant repellency for 2 h, Tri-Tec 14TM which showed significant (P < 0.05) repellency with respect to controls for 2 h and Stomoxin which showed significant (P < 0.05) repellency for 1 h. As the active ingredient of Stomoxin is permethrin, this indicates that recommendations to spray animals with this insecticide to prevent the spread of C.imicola-borne pathogens will not be useful. The repellents superior to DEET were: the plant-derived material Ag 1000 that repelled significantly (P < 0.05) with respect to controls for up to 4 h following a similar pattern to but somewhat more strongly than DEET, and pyrethroid-T which exerted significant (P < 0.05) repellency for 9 h. Pyrethroid-T proved to be the best repellent tested, and if sprayed nightly it might provide protection from C.imicola-borne pathogens.