Age-related changes in the competency of the pheromone gland and the pheromonotropic activity of the brain of both virgin and mated females of two Choristoneura species

Nine-day-old decapitated females injected with different doses of Hez-PBAN produced significantly less pheromone than 1-day-old individuals, suggesting that the age-related decline in the pheromone titre of Choristoneura fumiferana and C. rosaceana virgin females was primarily the result of a reduced ability of the glands to produce pheromone. In C. fumiferana, lower pheromonotropic activity of the Br-SEG may also contribute to the pheromone decline with age but not in C. rosaceana, as the pheromonotropic activity of the Br-SEG remained constant throughout the females’ life. In both Choristoneura species, mating also suppressed pheromone production (pheromonostasis) after 24 h. The Br-SEG of mated females contained PBAN but there was no indication that its concentration changed with time post-mating since Br-SEG homogenates obtained from different-aged mated females showed the same level of pheromonotropic activity in both Choristoneura species. However, as observed in virgins, pheromone glands of older mated females were less sensitive to PBAN than those of younger ones. This suggests that the probability of Choristoneura females to attract a second mate may decrease with an increase in the refractory period following the first mating.