Differential impacts of the southern pine beetle, Dendroctonus frontalis, on Pinus palustris and Pinus taeda Nicholas A. Friedenberg, Brenda M. Whited, Daniel H. Slone, Sharon J. Martinson, and Matthew P. Ayres Abstract: Patterns of host use by herbivore pests can have serious consequences for natural and managed ecosystems but are often poorly understood. Here, we provide the first quantification of large differential impacts of the southern pine bee- tle, Dendroctonus frontalis Zimmermann, on loblolly pine, Pinus taeda L., and longleaf pine, Pinus palustris P. Mill., and evaluate putative mechanisms for the disparity. Spatially extensive survey data from recent epidemics indicate that, per square kilometre, stands of loblolly versus longleaf pine in four forests (380–1273 km 2 ) sustained 3–18 times more local infestations and 3–116 times more tree mortality. Differences were not attributable to size or age structure of pine stands. Using pheromone-baited traps, we found no differences in the abundance of dispersing D. frontalis or its predator Thanasi- mus dubius Fabricius between loblolly and longleaf stands. Trapping triggered numerous attacks on trees, but the pine spe- cies did not differ in the probability of attack initiation or in the surface area of bark attacked by growing aggregations. We found no evidence for postaggregation mechanisms of discrimination or differential success on the two hosts, suggest- ing that early colonizers discriminate between host species before a pheromone plume is present. Re ´sume ´: Le patron d’utilisation des ho ˆtes par les ravageurs herbivores peut avoir de se ´rieuses conse ´quences pour les e ´co- syste `mes naturels et ame ´nage ´s mais elles sont souvent mal connues. Dans cet article, nous quantifions pour la premie `re fois les impacts du dendroctone me ´ridional du pin, Dendroctonus frontalis Zimmermann, qui sont tre `s diffe ´rents sur le pin a ` en- cens, Pinus taeda L., et le pin des marais, Pinus palustris P. Mill., et nous e ´valuons les me ´canismes qui pourraient expliquer cette disparite ´. Les donne ´es d’un inventaire couvrant un vaste territoire et portant sur des e ´pide ´mies re ´centes indiquent que les peuplements de pin a ` encens ont subi 3–18 fois plus d’infestations locales et 3–116 fois plus de mortalite ´ par kilome `tre carre ´ que les peuplements de pin des marais dans quatre fore ˆts (380–1273 km 2 ). Ces diffe ´rences n’e ´taient pas attribuables a ` la structure d’a ˆge ou de dimension des peuplements de pin. A ` l’aide de trappes appa ˆte ´es avec des phe ´romones, nous n’avons observe ´ aucune diffe ´rence dans l’abondance de D. frontalis alors qu’il se dispersait ni de son pre ´dateur, Thanasimus dubius Fabricius, entre les peuplements de pin a ` encens et de pin des marais. Le pie ´geage a provoque ´ plusieurs attaques sur les ar- bres mais il n’y avait pas de diffe ´rence entre les espe `ces de pin quant a ` la probabilite ´ du de ´clenchement d’une attaque ni quant a ` la superficie d’e ´corce attaque ´e par le regroupement d’un nombre croissant d’insectes. Nous n’avons trouve ´ aucun in- dice de discrimination ou de diffe ´rence de succe `s dues a ` des me ´canismes de regroupement a posteriori sur les deux ho ˆtes, ce qui indique que les insectes pionniers distinguent l’espe `ce ho ˆte avant qu’une traı ˆne ´e de phe ´romone soit pre ´sente. [Traduit par la Re ´daction] Introduction Within ecological communities, consumers inevitably use a subset of potential resources. Even within the niche of a generalist consumer, some resources are used more than others. In the case of forest pests, identifying the mecha- nisms that determine which host species are impacted and to what degree is fundamental to managing forests for resil- ience against widespread damage (Graham 1939; Carnus et al. 2006). For instance, differential impacts on populations that serve as resources may reflect either active resource preference on the part of the pest or differential success fol- lowing indiscriminant attacks; either of these alternatives could result from variation among host species in availabil- ity or suitability. Realized host availability could be a sim- ple reflection of biomass but could also be influenced by age structure and (or) spatial dispersion. Realized host suit- ability could be a function of primary nutritive quality, effi- cacy of defenses, or even differences in species associations between hosts and predators, competitors, or mutualists of Received 31 October 2006. Accepted 5 January 2007. Published on the NRC Research Press Web site at cjfr.nrc.ca on 15 September 2007. N.A. Friedenberg, 1 B.M. Whited, 2 S.J. Martinson, and M.P. Ayres. Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA. D.H. Slone. 3 USDA Forest Service, Southern Research Station, 2500 Shreveport Highway, Pineville, LA 71360, USA. 1 Corresponding author (e-mail: naf@archidictus.org). 2 Present address: Graduate Program in Organismic and Evolutionary Biology, University of Massachusetts, Amherst, MA 01003, USA. 3 Present address: US Geological Survey Sirenia Project, 2201 NW 40th Ter., Gainesville, FL 32601, USA. 1427 Can. J. For. Res. 37: 1427–1437 (2007) doi:10.1139/X07-008 # 2007 NRC Canada