Temporal and temperature-induced changes in emission rates and blend ratios of sex pheromone components in Trichoplusia ni

Moths that use pheromone components with different vapor pressures either must have active means of regulating the emitted blend or must be able to respond to a wider range of ratios of these components. Both temperature and previous depletion of pheromone reserves could challenge the ability of a female to maintain a constant pheromone blend ratio and emission rate. Therefore this study of the influence of temperature and time of night on pheromone emission rates and blend ratios was conducted. Increases in temperature from 15 to 30°C resulted in a significant increase (70%) in pheromone emission rate from forcibly extruded sex pheromone glands of female cabbage looper moths, Trichoplusia ni. Blend ratios of (Z)-7- and (Z)-9-tetradecenyl acetate (Z7- and Z9-14:Ac) relative to the major pheromone component (Z)-7-dodecenyl acetate (Z7-12:Ac) increased significantly with temperature. During all time periods in the scotophase, the percentages of the gland's contents of each pheromone component emitted during a 10 min period (percent depletion rates) were different, with (Z)-5-dodecenyl acetate (Z5-12:Ac) and Z7-12:Ac having the highest depletion rates and Z7-14:Ac and Z9-14:Ac the lowest, reflecting their different vapor pressures. For each compound the percent depletion rate increased steadily during the scotophase, suggesting that either the permeability of the gland's membrane to each pheromone component increased, or that a pheromone transport system became increasingly active. This may compensate for lower pheromone reserves at the end of the scotophase to maintain a relatively stable pheromone emission rate. Blend ratios of Z7-14:Ac and Z9-14:Ac in both pheromone gland extracts and volatile collections increased over the scotophase. This was likely caused by lower vapor pressures of the two 14-carbon acetates and thus a relative accumulation of these on or in the gland.