INEFFICACY OF COURTSHIP STRIDULATION AS A PREMATING ETHOLOGICAL BARRIER FOR IPS BARK BEETLES (COLEOPTERA, SCOLYTIDAE)

Courtship displays se-e many species of animals for discerning potential mates and their relative qualities. Models for parapatric speciation predict that in regions where species meet, selection will result in the spread of heritable behavioral characters that favor the rejection of potential heterospecific mates before mating, thus reinforcing postmating barriers through evolution of premating isolation. A trio of closely related pine bark beetle species-Ips confusus Le Conte, 1. paraconfusus Lanier, and I. hoppingi Lanier-Populate narrow bands of sympatry in the montane regions of the American Southwest. Their male-produced aggregation pheromones are highly cross-attractive to both sexes. A fourth species, I. lecontei Swaine, is broadly sympatric with one member of the trio, but is more distantly related and is not attracted to the pheromone of other sympatric species. Female Ips stridulate as they attempt to enter male nuptial chambers. Each of these species produces a unique signal. However, males of the four species readily accepted females of their sibling species during courtship, whereas they rejected more distantly related females. We suggest that the divergence of courtship behavior is the result of phylogenetic divergence, not the result of reinforcing selection or reproductive character displacement for the prevention of heterospecific mating.