Potential tradeoffs of pheromone-based mate location and enhancing host-plant defenses

Many insect species use pheromones to attract and locate mates. We recently discovered that male goldenrod gall flies (Eurosta solidaginis) emit very large quantities of a volatile emission that appears to function as a sex pheromone. Recent research from our lab has also revealed that the flies’ host plant, tall goldenrod (Solidago altissima) can perceive the emission of this specialist herbivore and respond by enhancing its anti-herbivore defenses. Organisms are often under sexual selection to express otherwise expensive or costly traits that their mates find attractive, thereby increasing their likelihood to reproduce. We hypothesize that E. solidaginis males are under sexual selection to emit large quantities of this putative sex attractant, despite the cost of providing a cue for S. altissima plants to enhance their defenses and subsequently reduce larval performance. The goals of this study were to 1. characterize the volatile emission of male E. solidaginis, 2. examine potential correlations between pheromone production and physical characteristics of individual male flies, including mass, gall-size, and life span, and 3: investigate how the concentration of the E. solidaginis volatile emission influences attractiveness to female flies.