Association, population dynamics, and underlying behaviors of bark beetle predators in the health of red pine plantations (Pinus resinosa)

Stem and root colonizing beetles, and their associated staining fungi and predators, were associated with declining red pine, Pinus resinosa, stands in Wisconsin. Monitoring of seventeen declining and healthy plantations over 3 years showed that populations of predators of Ips, particularly Thanasimus dubius, Platysoma cylindrica, and P. parallelum , were higher in healthy stands. Declining stands had more lower stem infesting Dendroctonus valens and Pissodes spp. Furthermore, declining stands had higher Ips and lower predator populations early in the season, whereas healthy stands had higher numbers of predator populations early in the season. Populations of root weevils were higher in healthy stands early in the season, but were higher in declining stands later in the season. The staining fungi Leptographium procerum and Leptographium terebrantis were more frequently isolated from roots in declining than healthy stands and more frequently associated with trees at the pocket margin than in the asymptomatic portions of declining stands.; Thanasimus dubius and P. cylindrica were attracted to cues associated with feeding on bark-phloem disks by two scolytids that produce adult pheromones, I. pini and I. grandicollis, but not to other phloeophagous species that colonize the same trees.; We conducted additional experiments to evaluate the responses of bark beetles and their predators to various blends of Ips spp. pheromones and conifer monoterpenes. Ips pini were not attracted to monoterpenes alone. However, with the exception of 3-carene, the effect of monoterpenes on I. pini's response to its pheromone, ipsdienol plus lanierone, was inhibitory. In contrast, (−)-α-pinene both attracted I. grandicollis, and enhanced the attraction of I. grandicollis to its pheromone, ipsenol. No monoterpene inhibited the response of I. grandicollis to its pheromone. Monoterpenes alone were not attractive to predators. However, some monoterpenes, such as myrcene and to a lesser extent 3-carene, reduced, whereas others, such as α-pinene, consistently enhanced, predator attraction to the pheromones of their Ips prey. Furthermore, (+)-α-Pinene synergized predator responses to the pheromone of I. pini, whereas (−)-α-pinene synergized responses to the pheromone of I. grandicollis. This pattern occurred for all major predator species.