Effect of pheromone dosage on the mating disruption of Douglas-fir tussock moth

Z-6-heneicosen-11-one, the major synthetic component of the sex pheromone of Douglas-fir tussock moth, Orgyia pseudotsugata (McDunnough), was used to disrupt insect mating. Dosages of 72, 36, 18, and 9 g/ha of the synthetic pheromone in polyvinyl chloride beads were each applied to three 2-ha plots using conventional aerial spray equipment. Observation of the spraying operation, and catches of male moths in traps baited with standardized synthetic pheromone indicated that two of the 12 plots were not completely sprayed. The efficacy of mating disruption was monitored over the 9 weeks following spraying, using traps baited with feral females interspersed among the standardized traps. When trap catches by feral females in the two unsprayed plot sections were discarded, the mean catch increased as the synthetic dosage decreased. These catches compared with those in the untreated plots were reduced ovcr 99.5% in plots treated with dosages of 72, 36, or 18 g/ha; and by 97.5% with a dosage of 9 g/ha of synthetic pheromone. In our experimental conditions, the difference in numbers of trapped males among the 72, 36, 18, and 9 g/ha dosage groups was marginally nonsignificant. Our data thus indicate that in operational use, dosages near or below 9 g/ha would be significantly different in effectiveness from the 3 higher dosages.Key words: dosage; tussock moth; pheromone; mating disruption; Orgyia pseudotsugata; Lepidoptera:Tortricidae; biological contro