A contact mating pheromone in the biting midge,Culicoides melleus

A hexane-soluble contact mating stimulant pheromone, bioassayable by sexual response of tethered males, was extracted by prolonged (5-day) washing of whole, freshly-killed male and female Culicoides melleus. Assays were performed by allowing males to manipulate (with their feet) very small cubes of cork on which extract had been deposited by evaporation. Silica-gel chromatography of crude extract yielded total hydrocarbon fractions to which, when assayed at 10 ♀♀ (or ♂♂) equivalents. 75% or more of the males responded. The diluted total hydrocarbon fraction from females elicited significant male response at 1 ♀ equivalent, but not at $\text{1}\text{10}$ equivalent or less. Assays of synthetic n-alkanes showed no activity, but among several methyl-substituted alkanes (2-methyl-docosane, 8-methyl-docosane, 9-methyl-tricosane, 10-methyl-docosane), the first three produced significant response assayed at 1 μg per model.