Periodicity in the quantity and blend ratios of pheromone components in glands and volatile emissions of mutant and normal cabbage looper moths, Trichoplusia ni

Abstract

Pheromone release behaviour, pheromone content of glands, and volatile emission rates of pheromone from female Trichoplusia ni were determined during the 24 h photoperiodic regime. Periodic changes in the quantity and blend ratios of pheromone emitted from forcibly extruded glands were similar for normal females and females that express a mutant gene for an abnormal pheromone phenotype. Both types of females exhibited a diel periodicity in the emission rate and gland content of ( Z)-7-dodecenyl acetate (Z7-12:Ac), the major component. Emission rates of this compound were low during the photophase, rose rapidly at the beginning of the scotophase, and then decreased later in the scotophase. In contrast, the amount of Z7-12:Ac in glands increased during the photophase and then decreased throughout the scotophase. Periodicity in the amount of 12-carbon acetate minor components in volatile emissions and glands followed the same pattern as Z7-12:Ac, thus their relative proportions (proportions relative to Z7-12:Ac) remained constant during light and dark periods. In contrast, the relative proportion of the 14-carbon acetate components in volatile emissions rose during the scotophase and then decreased during the photophase. Our results suggest that: (1) normal and mutant females are similar in terms of photoperiodic regulation of pheromone biosynthesis, pheromone release behaviour, and pheromone emission despite the differences in the pheromone blend of the two types, (2) pheromone biosynthesis is continuous, (3) periodicity in emissions is a manifestation of an underlying periodicity in transport of pheromone to the gland's surface that is correlated with pheromone release behaviour but not pheromone biosynthesis, and (4) pheromone blend ratios change during the course of the pheromone release period because of different vapour pressures of the pheromone components.