Novel diffusion-dilution method for release of semiochemicals: Testing pheromone component ratios on western pine beetle.

Each of the pheromone components of the Western pine beetle,Dendroctonus brevicomis LeC. (Coleoptera: Scolytidae), exo-brevicomin (E) and frontalin (F), were released in the forest at various ratios 0.01∶1, 0.1∶1, or 1∶1 to a constant dose of the opposite component (E or F) plus the host monoterpene myrcene (M), which were each released at 1.5 mg/day. The components were released by a new method that combines the principles of chemical diffusion through a tube with mole percentage dilution of the chemical. Both sexes ofD. brevicomis were attracted similarly at comparable ratios (and release rates) of E or F and showed similar logarithmic relationships (r (2)=0.92∓0.99). The bark beetle predator,Temnochila chlorodia (Mannerheim) (Coleoptera: Trogositidae) was apparently less sensitive to E thanD. brevicomis, being relatively less attracted to amounts of E equivalent to that released by 70 females, while none were attracted to that from seven females (while this rate still attracted significant numbers of conspecifics). The apparent insensitivity of bark beetles to extreme ratios between pheromone components in contrast to moths is discussed. The advantages of the diffusion-dilution method of releasing semiochemicals compared to previous methods of absorbents, wicks, capillary tubes, and semipermeable plastic membranes are also discussed.