DAILY ACTIVITY PATTERNS AND SEX PHEROMONE SPECIFICITY AS SEXUAL ISOLATING MECHANISMS IN TWO SPECIES OF CHORISTONEURA (LEPIDOPTERA: TORTRICIDAE)

Abstract

The roles of adult activity patterns and sex pheromones were investigated in the sexual isolation of Choristoneura fumiferana and C. pinus, species which hybridize in cages but not in the field. Female C. fumiferana started calling (extruding the sex pheromone gland) earlier (50% of the females started calling by sunset) than female C. pinus (50% by 11/2 hours after sunset). Male C. fumiferana were also attracted to traps by the females earlier, although the times of the peak catches were approximately the same in both species. Males, both in the laboratory and the field, responded only to the sex pheromone of their own species. It is therefore concluded that while C. pinus adults normally appear about 2 weeks later than those of C. fumiferana, which reduces the possibility of hybridization, when the adults do overlap, the ultimate barrier is the specificity of the sex pheromones.