Intra-Annual Variation in Responses by Flying Southern Pine Beetles (Coleoptera: Curculionidae: Scolytinae) to Pheromone Component endo-Brevicomin.

The southern pine beetle Dendroctonus frontalis Zimmermann (Coleoptera: Curculionidae: Scolytinae) is attracted to an aggregation pheromone that includes the multifunctional pheromone component endo-brevicomin. The effect of endo-brevicomin on attractive lures varies from strong enhancement to reduction of beetle attraction depending upon release rate, lure component spacing, and proximity of beetle infestations. Anecdotal observations have further suggested that the effects of endo-brevicomin vary during the year. We investigated this possibility under nonoutbreak conditions in southwestern Mississippi where for two-and-a-half years we monitored traps baited with frontalin and the host odor alpha-pinene either (a) alone, or with an endo-brevicomin release device either (b) located directly on the trap, or (c) displaced 6 m away. The endo-brevicomin devices in our tests increased D. frontalis catches during all times of year, and 6 m displacement of the endo-brevicomin release device from the trap did not significantly alter responses except during the spring flight peak when displacement increased catches. Our data suggest that flying D. frontalis have a stronger tendency to avoid the immediate proximity of a release point of endo-brevicomin during their springtime dispersal flight when catches are greatest. Catches of Thanasimus dubius (F.) (Coleoptera: Cleridae), a major predator of D. frontalis, were not altered by endo-brevicomin, and ratios of D. frontalis to T. dubius changed over the course of the year. We discuss the possible effects of intra-annual variation in D. frontalis response to endo-brevicomin both on beetle attack behavior and use of endo-brevicomin as a lure adjuvant in D. frontalis population monitoring.

Characterization of an aggregation pheromone in Hylesinus pruinosus (Coleoptera: Curculionidae: Scolytinae).

We conducted laboratory and field bioassays to characterize the pheromone system of an ash bark beetle, Hylesinus pruinosus Eichhoff (Coleoptera: Curculionidae: Scolytinae). Solitary females in newly initiated galleries in ash logs produced (+)-exo-brevicomin, whereas male beetles paired with females produced (+)-endo-brevicomin, lesser quantities of (+)-exo-brevicomin, and a third compound that could not be identified. Beetles produced these compounds also after exposure to juvenile hormone III, and they were the sole volatile chemicals isolated from beetles or aerations of infested logs that elicited electrophysiological responses from antennae of either sex. In the field, both sexes were strongly attracted to traps baited solely with either racemic or pure (+)-endo-brevicomin. Racemic exo-brevicomin was much less attractive to both sexes than racemic endo-brevicomin, and it did not increase attraction of endo-brevicomin when released in combination. Host odors (volatiles from mechanically damaged ash branches) failed to attract beetles or increase attractiveness of racemic exo-brevicomin. Our evidence suggests that male-produced (+)-endo-brevicomin is the major component of an aggregation pheromone for H. pruinosus, with (+)-exo-brevicomin and the unidentified male compound playing an indeterminate role in the chemical ecology of this species. Our data thus show an instance in which the major aggregation pheromone component of a bark beetle is produced by the secondarily arriving sex, a rare occurrence in bark beetles but one which has been reported previously for the Hylesini.