Selective manipulation of predators using pheromones: responses to frontalin and ipsdienol pheromone components of bark beetles in the Great Lakes region

1 One proposed approach to improving biological control of bark beetles (Coleoptera: Scolytidae; alt. Curculionidae: Scolytinae) is to manipulate predator movement using semiochemicals. However, selective manipulation is impeded by attraction of both predators and pests to bark beetle pheromones. 2 The primary bark beetle affecting pine plantations in Wisconsin, U.S.A., is the pine engraver, Ips pini (Say). Other herbivores include Ips grandicollis (Eichhoff) and Dryophthorus americanus Bedel (Curculionidae). The predominant predators are the beetles Thanasimus dubius (Cleridae) and Platysoma cylindrica (Histeridae). 3 We conducted field assays using two enantiomeric ratios of ipsdienol, and frontalin plus alpha-pinene. Ipsdienol is the principal pheromone component of L pini, and frontalin is produced by a number of Dendroctonus species. alpha-Pinene is a host monoterpene commonly incorporated into commercial frontalin lures. 4 Thanasimus dubius was attracted to frontalin plus alpha-pinene, and also to racemic ipsdienol. By contrast, I. pini was attracted to racemic ipsdienol, but showed no attraction to frontalin plus alpha-pinene. Platysoma cylindrica was attracted to 97%-(-)-ipsdienol and, to a lesser extent, racemic ipsdienol, but not to frontalin plus alpha-pinene. Ips grandicollis was attracted to frontalin plus alpha-pinene but not to ipsdienol. Dryophthorus americanus was attracted to both ipsdienol and frontalin plus alpha-pinene. 5 This ability to selectively attract the predator T. dubius without attracting the principal bark beetle in the system, L pini, provides new opportunities for research into augmentative biological control and basic population dynamics. Moreover, the attraction of T. dubius, but not P. cylindrica, to frontalin plus alpha-pinene creates opportunities for selective manipulation of just one predator. 6 Patterns of attraction by predators and bark beetles to these compounds appear to reflect various degrees of geographical and host tree overlap with several pheromone-producing species.