Genetic Basis of Semiochemically Mediated Bark Beetle-Predator Coevolution: Implications for Developing Mass-Trapping Technologies

Background The pheromone chemistry of Ips pini (Coleoptera: Scolytidae) has been extensively studied in recent years. In eastern North America, I. pini populations respond most strongly to ipsdienol with an enantiomeric composition of about 40 percent to 75 percent-(S)-(+) (Herms and others 1991, Lanier and others 1980, Raffa and Klepzig 1989, Teale 1990). In western populations, I. pini typically responds maximally to ipsdienol with an enantiomeric composition of 93 percent to 100 percent-(R)-(-) (Lanier and others 1980, Miller and others 1989, Seybold and others 1992d). In eastern populations of I. pini, both isomers of ipsdienol function as attractants (Teale 1990), whereas in most western populations the (-)-isomer serves as an attractant and the (+)isomer functions as an interruptant (Birch and others 1980, Seybold and others 1992d). Recently, lanierone was demon­ strated to be an important component of the aggregation phero­ mone of eastern populations of I. pini (Teale and others 1991), but it was not found in western populations (Seybold and others 1992c). Teale (1990) demonstrated in I. pini that the chirality of male-produced ipsdienol was heritable. In addition, Teale and others (personal communication) have shown a strong, positive correlation between male response to and production of enan­ tiomeric blends of ipsdienol. If positive assortive mating were common among individuals with similar ipsdienol preference/ production, then genetic substructuring of I. pini populations could easily occur. Moreover, if movement by Ips adults were limited between habitat patches (e.g., isolated pine woodlots), then further genetic divergence could result on a spatial scale. Thanasimus dubius (Coleoptera: Cleridae) is a specialist predator of Ips and other bark beetles, and can cause significant bark-beetle mortality (Riley and Goyer 1986, and references therein). Thanasimus dubius uses the pheromone of I. pini as a kairomone in prey location, and like I. pini, demonstrates prefer­ ences among different blends of ipsdienol (Herms and others