In both Choristoneura species, the periodicity of calling and pheromone production is well synchronized, with maximal activity occurring during the early scotophase. Newly-emerged females decapitated prior to the onset of the scotophase produced no or very little pheromone, but the injection of PBAN or Br-SEG extracts restored normal pheromone production. Transection of the ventral nerve cord (VNC) did not affect pheromone production in controls females or in decapitated females injected with PBAN or Br-SEG extracts. These results clearly indicate that the regulation of pheromone production is not neurally mediated in either Choristoneura species. Furthermore, there was no evidence of PBAN-like factors in hemolymph collected during the calling period. However, while the presence of the bursa copulatrix (BC) was essential to produce pheromone, an extract of the BC injected into decapitated females did not elicit pheromone production. In both species, mating significantly depressed the pheromone titre 24 h later. However, on subsequent days, pheromone production increased in C. fumiferana but not in C. rosaceana. Male accessory gland extracts or hemolymph taken from mated females did not have pheromonostatic activity. However, pheromone production in mated females was not inhibited when the VNC was transected prior to mating, indicating that the integrity of the central nervous system is required to permanently switch off pheromone production. As suggested for other species, the presence of sperm in the spermatheca probably triggers the release of a signal, via the VNC, to inhibit pheromone production. Therefore, we speculate that in mated C. fumiferana females, the neural signal declines following the depletion of sperm in the spermatheca, and as it is less effective in preventing the release of PBAN there is a resumption of pheromone production. Mating induces a significant rise in the JH tire of both female moths, suggesting that the post-mating pheromone suppression may also be under hormonal regulation. Following injection of JH pheromone titres only declined in C. rosaceana virgins. This suggests that the significant post-mating rise in the hemolymph JH titre in this species plays a role in keeping the pheromone consistently low throughout reproductive life. These findings will be discussed in relation with the different life histories exhibited by the two Choristoneura species.

Index term: Choristoneura fumiferana, Choristoneura rosaceana, PBAN, bursa, JH

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