Factors contributing to variation in cuticular hydrocarbon profiles of two species of longhorned beetles (Coleoptera: Cerambycidae)

The insect cuticle is comprised of a matrix of chitin and proteins, topped with a thin layer of wax.  Hydrocarbons in the waxy layer are coopted for communication in many insects, and a subset of these hydrocarbons serve as sex-specific mate recognition signals, also known as contact pheromones.  The relative abundance of hydrocarbons can be altered by a variety of environmental factors, such as nutrition, temperature, and relative humidity, potentially affecting individual fitness.  I investigated factors influencing cuticular hydrocarbon intraspecific variation of two species of longhorned beetles native to eastern North America, Neoclytus acuminatus (F.) and Xylotrechus colonus F.  Body size of adult beetles was significantly associated with the relative amounts of some, but not all, contact pheromone components and non-pheromone hydrocarbons.  The relative abundance of hydrocarbons, including contact pheromones of X. colonus, varied significantly during the seasonal flight period.  Cuticular hydrocarbons of N. acuminatus also varied significantly in relative abundance spatially, both across small geographical distances in east-central Illinois (≤ 55 km), and more distantly between populations in Illinois and Pennsylvania.  Profiles varied across body regions of individual beetles, suggesting that sampling only one portion of the body by SPME may not yield a profile that is truly characteristic of the species, especially with regard to contact pheromones.  Whole body hexane extraction was confirmed to be an accurate representation of the hydrocarbon profile.  In summary, this study provides evidence that hydrocarbon profiles of insects are dynamic, varying spatially and temporally, and may be influenced by environmental factors.