Abstract Z-6-Heneicosen-11-one (1) and Z-1, 6-Heneicosen-11-one (2) are the sex pheromones of the Douglas-Fir Tussock moth,'Orgyia Pseudo Sugata', isolated1, 2 in 1975 and 1978 respectively. In contrast with other lepidopterous pheromones, which are unsaturated C12-C14 primary alcohols or acetates, these were found to be C21 ketones. The Douglas-Fir Tussock moth is a severe defoliator of the Fir forest; consequently, ...