Potential for evolution of resistance to pheromones - Worldwide and local variation in chemical communication system of pink bollworm moth, Pectinophora gossypiella

Female Pectinophora gossypiella (Saunders) from most of the desert cotton-growing areas of southern California emitted significantly more pheromone in 1984 and 1985 than in preceding years (1982 and 1983). This increase amounted to almost 20% by 1985. It is unlikely that this small change would represent effective resistance to disruptant pheromones, but this increase could reflect the result of selection pressure imposed by the use of mating disruption for population control. A worldwide survey of emitted pheromone from this species found that there was much more variation in the emission rate than the blend ratio of the two pheromone components. The emitted blend ratio was remarkably consistent over time (in southern California) and throughout the worldwide range of the insect. Small differences in the blend ratio that were detected probably have no major biological significance because of the relatively broad response spectrum of males to changes in the blend of pheromonal components. Populations of males did not consist of several phenotypes, each with a different preference for specific blend ratios. Rather, the broad response spectrum to blend ratios in a population can be attributed to variation in the response of any individual. Therefore, selection for a response phenotype that is narrowly tuned to the blend emitted by females may be difficult.