Climatic warming over recent decades has been permitting northern range expansions of many species, including a number of forest pests. More range expansions are predicted in coming years, yet our current understanding of the role of the indigenous ecological community in resisting or facilitating the expansion of nonindigenous pests is lacking. The southern pine beetle, Dendroctonus frontalis, has been expanding northward and has been present in New Jersey since 2001, more than sixty years after the last records. Southern pine beetles in the New Jersey Pinelands join an indigenous community that includes numerous less aggressive bark beetles, as well as their predators, microbial symbionts, and hosts. Because it is common for suitable host trees to be limiting, and for pheromones to attract other species, community interactions are notoriously strong in bark beetle systems. Since 2007, we have employed pheromone-baited traps to characterize the community of bark beetles and their predators at six sites in the New Jersey Pinelands. Measuring response to traps baited with different combinations of pheromones also allows us to estimate the importance of predation and direct competitive interactions within the bark beetle community.
Results/Conclusions
Abiotic factors, predation, and competition may all play a role in limiting the success of southern pine beetles in the New Jersey Pinelands. While they have spread north throughout the entire Pinelands area, southern pine beetle population densities remain lower at sites in the northern part of this range, suggesting that their expansion to the north continues to be limited by climatic constraints. The main bark beetle predator in the area, the clerid beetle Thanasimus dubius, demonstrates a significant preference for the southern pine beetle pheromone frontalin over that of other bark beetles. Predator densities are also highest at sites with higher southern pine beetle infestations, suggesting that predation pressure may play an important role in limiting the growth of southern pine beetle populations. Other important pine bark beetle species include Ips avulsus, and Ips grandicollis. While all species respond in higher densities to a trap baited with their own pheromone, captures of southern pine beetles do not appear to be lowered by the presence of another pheromone, while those of I. grandicollis do. All species appear to respond in lower numbers when three pheromones are present. These preliminary results suggest that pheromones may aid niche partitioning; ongoing work seeks to quantify competition effects on host material directly.
