POSSIBLE ROLE OF MALE PHEROMONES IN THE REPRODUCTIVEISOLATION OF TWO RACES OF FALL ARMYWORM.

Jeremy N. McNeil
Dept. of Biology, Laval University, Ste.-Foy, Canada, G1K 7P4.

Two distinct host races of fall armyworm have been identified and althoughthey occur sympatrically there appears to be very little hybridizationin the field. The female calling period of the two races are temporallyseparated and the pheromone titres in the glands of the “corn” strain femalesis significantly higher than those of the “rice” strain. However, despitethese differences, a proportion of the males of one strain still respondto calling females of the other strain. No-choice and choice mating experimentswere carried out to examine the possibility that males pheromones playa role in the reproductive isolation of the two races. “Corn” females seldomaccept “rice” males, and actively reject courting males even if no otherpotential mates are present. In contrast, “rice” females show no preferenceand readily accept males of both strains. The existence of this asymmetricalmate choice will be discussed within the context of the temporal matingpatterns of the two races.