Field studies on efficacy of host odour baits for the biting midge Culicoides impunctatus in Scotland

The efficacy of some putative attractants for the biting midge Culicoides impunctatus (Goetghebuer) (Diptera: Ceratopogonidae) was assessed using odour-baited 'delta traps' and suction traps. 1-octen-3-ol was confirmed as a potent olfactory attractant for C. impunctatus when released at 0.06mg/h. Acetone (23mg/h) and a mix of six phenolic compounds (phenol, 3-ethylphenol, 4-ethylphenol, 3-methylphenol, 4-methylphenol and 4-propylphenol), at undetermined release rate, also significantly increased delta trap catches compared to unbaited controls. When tested in combination, there was evidence of synergism between CO2 (0.2L/min) and acetone, 1-octen-3-ol or cow urine, trap catches being, respectively, 4.7, 6.2 and 9.3-fold greater than for CO2 alone. Highest catches were obtained with triple bait combinations comprising cow urine + acetone + CO2 or cow urine + 1-octen-3-ol+CO2, which increased trap catches by X 22 and X 24, respectively, compared to CO2 alone. Culicoides impunctatus was found to be extremely sensitive to CO2 and responses, gauged over two field seasons, showed a significant dose-dependent increase in catch across the entire range of release rates (0.2-2.5 L/min). Responses to these release rates, ranging from small to large mammal equivalents, emphasized the important role of CO2 in host location by C. impunctatus. Uses of olfactory attractants for monitoring and control of Culicoides are reviewed on the basis of these results.