Contrasting Competitor and Predator Responses to a Short-Lived Southern Pine Beetle Outbreak: A Case Study

The southern pine beetle (SPB) Dendroctonus frontalis Zimmermann, is the most important insect pest of pines in the southeastern United States, with outbreaks often resulting in thousands of hectares of pine mortality. Natural enemies and competitors have been cited as significant regulators of SPB populations and, therefore, outbreaks. A recent outbreak on the Homochitto National Forest (NF) in Mississippi provided an opportunity to undertake a case study comparing population fluctuations of SPB, its major predator Thanasimus dubius, and its competitors, Ips bark beetles. Trap catches of all three were tracked through the course of the outbreak on the Homochitto NF as well as in two other forests with low or no SPB activity. The number of predators collected initially increased on the Homochitto NF in response to the SPB outbreak, but their impact on reducing infestation numbers was unclear. Numbers of Ips trapped were similar across all three forests, indicating that other factors were regulating SPB populations. The outbreak only lasted a single year, and its brevity likely limited the availability of host resources for natural enemy and competitor populations. Additional studies are warranted to explore the mechanisms affecting the extent and duration of SPB outbreaks, such as active forest management. Study Implications: The widespread application of cut-and-leave treatments during a short duration southern pine beetle (SPB) outbreak on the Homochitto National Forest did not result in immediate increased collections of Ips bark beetles, competitors of SPB. Similar population trends of Ips bark beetles in areas with and without SPB infestations suggest that other factors, such as climate, regulate population numbers. Low numbers of the main SPB predator, Thanasimus dubius, immediately preceded an outbreak, and trap collections increased after outbreak onset, reaffirming the importance of this natural enemy in SPB population fluctuations.

Effects of Ethanol and α-Pinene in a Generic Trap Lure Blend for Pine Bark and Wood-Boring Beetles in Southeastern United States

Managers of detection programs for bark and wood-boring beetles require cost-effective trap lure combinations that maximize species detections. A trapping study was conducted in 2012 to determine the effects of ethanol and α-pinene lures on beetle catches in traps baited with ipsenol and ipsdienol lures in a stand of Pinus taeda L. in north-central Georgia. Traps with all four compounds worked well for 20 of 25 species of bark and wood-boring beetles, and associated predators. Catches of Acanthocinus obsoletus (LeConte) and Monochamus titillator (F.) (Cerambycidae), Hylastes porculus Erichson, Hylastes salebrosus Eichhoff, Hylobius pales (Herbst), Orthotomicus caelatus (Eichhoff) (Curculionidae), Thanasimus dubius (F.) (Cleridae), and Temnoscheila virescens (F.) (Trogossitidae) in baited traps increased with the addition of ethanol and α-pinene with maximum catches in traps baited with all four compounds. Catches of Ips avulsus (Eichhoff) (Curculionidae) decreased with the addition of both compounds; the lowest numbers of I. avulsus and Ips grandicollis (Eichhoff) were caught in traps baited with all four compounds. α-Pinene increased catches of Buprestis lineata F. (Buprestidae), Ips calligraphus (Germar), Pachylobius picivorus (Germar) (Curculionidae), Corticeus spp. (Tenebrionidae), Lasconotus spp., and Pycnomerus sulcicollis LeConte (Zopheridae); ethanol had no effect on these species. Ethanol increased trap catches of Curius dentatus Newman (Cerambycidae), Dryoxylon onoharaense (Murayama) (Curculionidae) and Platysoma spp. (Histeridae); α-pinene reduced catches. The data suggest that ethanol and α-pinene should be retained with ipsenol and ipsdienol as a generic trap lure blend for pine bark and wood-boring beetles in southeastern United States.

Differential impacts of the southern pine beetle, Dendroctonus frontalis, on Pinus palustris and Pinus taeda

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 beetle, 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 km2) 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 Thanasimus dubius Fabricius between loblolly and longleaf stands. Trapping triggered numerous attacks on trees, but the pine species 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, suggesting that early colonizers discriminate between host species before a pheromone plume is present.

RESPONSE OF CONE AND TWIG BEETLES (COLEOPTERA: SCOLYTIDAE) AND A PREDATOR (COLEOPTERA: CLERIDAE) TO PITYOL, CONOPHTHORIN, AND VERBENONE

Field studies were conducted in the United States and Canada to determine the response of the white pine cone beetle, Conophthorus coniperda (Schwarz), and the red pine cone beetle, Conophthorus resinosae Hopkins, to two potential inhibitors, conophthorin and verbenone, of pheromone communication. Trap catches of male C. coniperda and C. resinosae were significantly reduced and generally declined with increasing concentrations of conophthorin in traps baited with the pityol, a female-produced pheromone. Verbenone did not significantly reduce trap catches of C. coniperda. Conophthorin, but not verbenone, significantly reduced cone attacks by C. coniperda when placed near cone clusters. The twig beetles, Pityophthorus cariniceps LeConte and Pityophthorus puberulus (LeConte), responded to traps with pityol and α-pinene baits alone or with conophthorin. Thanasimus dubius (F) (Coleoptera: Cleridae) was attracted to the pityol and α-pinene, but conophthorin had no effect on attraction of this generalist bark beetle predator. Verbenone significantly reduced trap catches of T. dubius in pityol-baited traps.