Responses by dendroctonus frontalis and dendroctonus mesoamericanus (Coleoptera: Curculionidae) to semiochemical lures in Chiapas, Mexico: Possible roles of pheromones during joint host attacks

In southern Mexico and Central America, the southern pine beetle Dendroctonus frontalis Zimmermann (Coleoptera: Curculionidae: Scolytinae) commonly colonizes host trees simultaneously with Dendroctonus mesoamericanus Armendáriz-Toledano and Sullivan, a recently described sibling species. We hypothesized that cross-species pheromone responses by host-seeking beetles might mediate joint mass attack, bole partitioning, and reproductive isolation between the species. Previous studies had indicated that D. frontalis females produce frontalin and that female D. mesoamericanus produce frontalin, endo-brevicomin, and ipsdienol (males of both species produce endo-brevicomin and possibly ipsdienol). In field trapping trials in the Mexican state of Chiapas, D. frontalis was attracted to the lure combination of turpentine and racemic frontalin; racemic endo-brevicomin enhanced this response. In a single test, D. mesoamericanus was attracted in low numbers to the combination of turpentine, racemic frontalin, and racemic endo-brevicomin after the addition of racemic ipsdienol; in contrast, racemic ipsdienol reduced responses of D. frontalis. Inhibition of D. frontalis was generated in both sexes by (+)- and racemic ipsdienol, but by (-)-ipsdienol only in females. Logs infested with D. mesoamericanus females (the pioneer sex in Dendroctonus) attracted both species in greater numbers than either D. frontalis female-infested or uninfested logs. Our data imply that D. frontalis may be more attracted to pioneer attacks of D. mesoamericanus females, and that this could be owing to the presence of endo-brevicomin in the latter. Possible intra- and inter-specific functions of semiochemicals investigated in our experiments are discussed.