Semiochemistry of Cerambycid Beetles: Interactions Among Pheromones, Host Plant Volatiles, and Density Dependent Effects

Longhorn beetles (Coleoptera: Cerambycidae) are wood-boring insects that infest trees and woody plants of varying conditions, from healthy to dead. Pheromones have now been identified for a number of cerambycid species, but our understanding of pheromone use in the family is limited. The first section of my research investigated the role of host plant volatiles on attraction to pheromones, and sought to identify new host volatiles that may be attractive or synergistic, particularly for oak-infesting species. My results corroborated previous work demonstrating that conifer volatiles are synergists for some species of conifer-infesting cerambycids; no such effect was found for oak volatiles and oak-infesting species, however. The second portion of this dissertation examined how cerambycids utilize their pheromones, focusing on several species that use male-produced pheromones, which attract both sexes and are often not species-specific compounds. Several possible pheromone partitioning mechanisms were tested, and I found that diel activity periods and pheromone blends have roles in reproductively and/or competitively isolating cerambycid species that use similar or the same pheromone components. Although not directly tested, there is evidence that host plant volatiles may play a role in partitioning and isolation as well. Evidence was also found that males of one species, Phymatodes grandis, may exploit the volatiles emitted by males of another species, Phymatodes obliquus, as a kairomone. Response to increasing release rates of two common pheromone components, 2-methylbutan-1-ol and 3-hydroxyhexan-2-one, was also tested and I found that responses increased with release rates for four of the five test species, even at the highest rates tested (~1,450 μg/h and ~720 μg/h, respectively). However, responses of the fifth species, P. obliquus, did plateau with increasing release rates. I also tested the effect of density of conspecific males on per capita pheromone production. Headspace volatiles of male P. grandis were sampled from individuals, pairs, or groups of three or four beetles held in 500 ml Teflon chambers. Emission rates of their pheromone (R)-2-methylbutan-1-ol were found to decrease with increasing density, suggesting that cerambycids may use optimal density strategies, as has been shown for other coleopteran species that utilize male-produced sex-aggregation pheromones.