Body size influences levels of pheromone production in the longhorned beetles (Coleoptera: Cerambycidae): a result of larval host quality?

In many insects, adult body size is influenced by larval nutrition, with well-fed larvae becoming larger adults. Longhorned beetles attack woody host plants that vary in condition from healthy to weakened, stressed or even decomposing. Stressed hosts become available sporadically and unpredictably after they are damaged by such environmental factors as wind, lightning, fire, and drought. The suitability of these hosts to developing larvae declines rapidly, as the nutrient-rich subcortical tissues are degraded by various xylophagous competitors. Thus, selection may favor rapid host colonization of these hosts because larvae of first colonizers are afforded greater nutrition and increased body size than subsequent colonizers.  In this study, we test the hypothesis that variance in body size is greatest in species that attack stressed trees by measuring the elytron length of 2,263 longhorned beetles in 47 species and comparing the variances of those measurements between beetles that attack healthy, stressed or weakened hosts. The variance associated with body size of beetles that attack stressed hosts was significantly greater than those that attack healthy or weakened hosts, indicating that host condition affects the variability of beetle size. To test the hypothesis that larger beetles produce more pheromone, we weighed 26 male Neoclytus m. mucronatus and collected and quantified pheromone produced by individual beetles during each of their calling periods. Larger beetles produced significantly more pheromone, suggesting that larval nutrition may influence the ability of a male to recruit conspecifics for mating.