Sex pheromones in mate assessment: analysis of nutrient cost of sex pheromone production by females of the moth Heliothis virescens

Abstract

It has been postulated that sex pheromones, in addition to their role in mate recognition and/or finding, may also serve a role in assessment of mate quality. For this, a sex pheromone must give honest information about a signaler's quality, with honesty ensured by a direct metabolic or indirect fitness cost to the signaler. Using a stable isotope tracer-tracee method, we characterised the nutrient pools that fuel sex pheromone production in females of the moth Heliothis virescens, as well as the relative importance of larval- and adult-acquired nutrients to this process. Females used three pools for de novo biosynthesis of sex pheromone, haemolymph trehalose, glycogen (via trehalose), and fat, and produced ca. 25% of pheromone directly from stored (previously synthesised) precursor fatty acids. Pheromone was produced roughly equally from carbohydrate and fat. Adult feeding was very important for pheromone biosynthesis, with a maximum of 65% of de novo biosynthesised pheromone produced from a single adult feed (carbohydrate). Although these nutrient pools are shared with other reproductive physiologies, notably oocyte production, it is unlikely that pheromone production imposes a significant metabolic cost on females, because (i) the amount of nutrients used for pheromone production is negligible compared to that available, (ii) the haemolymph trehalose pool is readily replaceable throughout the adult life, and (iii) in mated females, carbohydrate shortages result in reduced allocation to pheromone.