Resource limitation reveals that high acetate levels in Heliothis subflexa sex pheromone blend are associated with reduced fitness

Sexual communication allows individuals to find and choose a mate, but also to avoid hybridization with individuals from different species. Sexual signals can thus play an important role in speciation. However, many sexual signals come with potential trade-offs with other life history traits, which may only be revealed under stressful conditions. To determine if intra-specific variation in sexual signals are affected by limited resource intake during the larval stage, we studied variation in the sex pheromone of the noctuid moth Heliothis subflexa when larvae were reared on limited resources. Females of this species produce acetate esters in their sex pheromone blend that attract males from the same species, while repelling a sympatrically occurring species, Heliothis virescens. As H. subflexa females produce high amounts of acetates when the interfering species is present but low amounts in its absence, we hypothesized that high-acetate sex pheromone signals trade off with female fitness. To identify potential trade-offs between high acetate levels and female fitness, we manipulated the quantity of resources available at the larval stage. We showed that under larval food stress, females with high ratios of acetates in their sex pheromone had longer developmental times and lower fertility compared to females producing less acetates. These results thus support our hypothesis that a balance between costly acetates and the benefit of deterring heterospecific mates may at least partly explain the intra-specific variation in the H. subflexa female sex pheromone blend.