Dynamics of pheromone production and communication in the mountain pine beetle, Dendroctonus ponderosae Hopkins, and the pine engraver, Ips pini (Sag) (Coleoptera : Scolytidae)

The mountain pine beetle, Dendroctonus ponderosae Hopkins, and the pine eng raver, Ips pini (Say), often co-exist in lodgepole pine, Pinus contorta var .latafolia Engelmann. Intra- and interspecific semiochemical communication occurs in both species and their complete semiochemical repertoire and prec ise dynamics of pheromone production have not been elucidated. Porapak-Q ex tracts of captured Volatiles from beetles of each species aerated at differ ent attack phases (freshly emerged, pioneer sex alone in the log and both s exes paired in new galleries), followed by gas chromatographic-electroanten nographic detection (GC-EAD) and GC-mass spectroscopic analyses identified 17 compounds (seven compounds common to both species, six present in D. pon derosae and four present in I. pini) that excited the antennae of either or both species. Seven compounds for D. ponderosae and nine for I. pini had n ot been assessed for behavioural activity. In field trapping experiments, 2 -phenylethanol produced by both species inhibited the response of D. ponder osae to its aggregation pheromones. exo- and endo-Brevicomin produced by D. ponderosae significantly decreased the response of I. pini to its aggregat ion pheromone ipsdienol. Nonanal, a ubiquitous compound found in the volati les of lodgepole pine, various nonhosts and in both beetle species deterred the response of I. pini to ipsdienol. The occurrence of cis-verbenol, tran s-verbenol and verbenone in emergent I. pini, and verbenone and 2-phenyleth anol in emergent D. ponderosae suggests that. these compounds may inhibit a ggregation and induce dispersal following emergence. Termination of aggrega tion in D. ponderosae appears to depend on the production of frontalin in c ombination with changes in the relative ratios of verbenone, exo-brevicomin , trans-verbenol and 2-phenylethanol. In I. pini, the cessation of ipsdieno l production by males is probably the main factor in terminating aggregatio n.