by Dr. Molly Darr | May 24, 2022 | 2011-2020 Publications, Southern Pine Beetle
Abstract
Drought has promoted large-scale, insect-induced tree mortality in recent years, with severe consequences for ecosystem function, atmospheric processes, sustainable resources and global biogeochemical cycles. However, the physiological linkages among drought, tree defenses, and insect outbreaks are still uncertain, hindering our ability to accurately predict tree mortality under ongoing climate change. Here we propose an interdisciplinary research agenda for addressing these crucial knowledge gaps. Our framework includes field manipulations, laboratory experiments, and modelling of insect and vegetation dynamics, and focuses on how drought affects interactions between conifer trees and bark beetles. We build upon existing theory and examine several key assumptions: (1) there is a trade-off in tree carbon investment between primary and secondary metabolites (e.g. growth vs defense); (2) secondary metabolites are one of the main component of tree defense against bark beetles and associated microbes; and (3) implementing conifer-bark beetle interactions in current models improves predictions of forest disturbance in a changing climate. Our framework provides guidance for addressing a major shortcoming in current implementations of large-scale vegetation models, the under-representation of insect-induced tree mortality.
To read the full article please visit the link below:
Huang, Jianbei, Markus Kautz, Amy M. Trowbridge, Almuth Hammerbacher, Kenneth F. Raffa, Henry D. Adams, Devin W. Goodsman, et al. 2020. “Tree Defence and Bark Beetles in a Drying World: Carbon Partitioning, Functioning and Modelling.” New Phytologist 225 (1): 26–36. https://doi.org/10.1111/nph.16173.
by Dr. Molly Darr | May 24, 2022 | 2011-2020 Publications, Southern Pine Beetle
Abstract
Key message: Increasing water use patterns were more spatially restricted than increased nitrogen in leaves and litterfall in mid-canopy sweetgum trees of varying proximity to overstory pines undergoing mortality.
Ecosystem changes following selective mortality of individual trees can be difficult to predict and depend on the response of surviving trees in the ecosystem. In the southeastern United States, southern pine beetle (Dendroctonus frontalis Zimmermann) selectively attacks and kills southern pines, particularly loblolly pine (Pinus taeda L.) which is prevalent throughout the region. Loss of loblolly pine should alter water and nutrient cycling unless co-occurring species are able to compensate for this lost functioning. The goals of this study were to determine changes in water and nutrient uptake of sweetgum trees (Liquidambar styraciflua L.) adjacent to loblolly pines experiencing mortality from girdling. We found that sweetgums near girdled pines initially used significantly less water, then similar amounts of water, then more water than sweetgums near control pines as pines experienced mortality. Relationships between daily sapflow and the natural log of vapor pressure deficit also differed significantly across years in sweetgums near girdled pines but not sweetgums near control pines. For sweetgum trees in both locations, both leaf and litterfall nitrogen content were significantly higher in the pine mortality year compared with the previous pine girdling year. Together, these results suggest that changes in water use are more spatially restricted to the region near dying pines whereas sweetgums, regardless of location, benefited from the extra available nitrogen in the ecosystem.
Keywords
Disturbance, Sapflow, Pinus taeda, Nutrient cycling, Succession
To read the full article please visit the link below:
Hornslein, Nicole J., Courtney Siegert, and Heidi J. Renninger. 2019. “Physiological Response of Mid-Canopy Sweetgum Trees to Overstory Loblolly Pine Mortality.” Trees-Structure and Function 33 (1): 139–51. https://doi.org/10.1007/s00468-018-1764-2.
by Dr. Molly Darr | May 24, 2022 | 2011-2020 Publications, Southern Pine Beetle
Abstract
1 Bark beetles are significant mortality agents of conifers. Four beetle species, the pine engraver Ips pini, the six-spined pine engraver Ips calligraphus sub. ponderosae, the southern pine beetle Dendroctonus frontalis, and the western pine beetle Dendroctonus brevicomis, cohabitate pines in Arizona.
2 A pheromone trapping study in ponderosa forests of Arizona determined the attraction of beetles to conspecific and heterospecific pheromone components in the presence and absence of host volatiles, and tested whether predators differ in their attraction to combinations of pheromone components and tree monoterpenes.
3 All four bark beetle species differed in their responses to heterospecific lures and monoterpenes. Ips calligraphus was the only species that increased in trap catches when heterospecific lures were added. Heterospecific lures did not inhibit the attraction of either Dendroctonus or Ips species. The replacement of myrcene with α-pinene increased the attraction of Dendroctonus, whereas the addition of α-pinene had mixed results for Ips. The prominent predators Temnochila chlorodia and Enoclerus lecontei were more attracted to the I. pini lure than the D. brevicomis
lure, and the combination of the two lures with α-pinene was most attractive to both predator species.
4 Cross attraction and limited inhibition of bark beetles to heterospecific pheromones suggest that some of these species might use heterospecific compounds to increase successful location and colonization of trees. Predator responses to treatments suggest that tree volatiles are used to locate potential prey and predators are more responsive to Ips than to Dendroctonus pheromone components in Arizona.
Keywords
Kairomones, pine engraver, pheromones, southern pine beetle, western pine beetle
To read the full article please visit the link below:
Hofstetter, Richard W., Monica L. Gaylord, Sharon Martinson, and Michael R. Wagner. 2012. “Attraction to Monoterpenes and Beetle-Produced Compounds by Syntopic Ips and Dendroctonus Bark Beetles and Their Predators.” Agricultural and Forest Entomology 14 (2): NIL_0094-NIL_0103.
by Dr. Molly Darr | May 24, 2022 | 2011-2020 Publications, Southern Pine Beetle
Abstract
Southern pine beetle (SPB; Dendroctonus frontalis Zimmerman), a native insect that has historically affected pine (Pinus spp.) ecosystems in the southeastern U.S., has recently expanded northward causing extensive tree mortality in pitch pine (P. rigida) and pitch pine-oak (Quercus spp.) forests of eastern Long Island, NY. Given the historic lack of SPB within this region, little is known regarding its potential impacts. This study examined the immediate effects of SPB-induced tree mortality and management (i.e., cut-and leave suppression) on the structure and composition of affected forest communities to inform management recommendations and projections of future forest conditions. Overstory pine basal area declined significantly following SPB infestation and management (67–100% mortality), although management partly mitigated these effects. There was no immediate impact of SPB or management on seedling and sapling density or composition, with hardwood species making up the majority of this layer and pine representing<6% of stems regardless of mortality agent. Pitch pine was less likely to be browsed by ungulates than white oak and scarlet oak. SPB infestation significantly increased snag basal area, whereas downed woody debris volumes were greatest following management. Understory community composition in pitch pine stands that had SPB or were managed had greater understory plant diversity largely through a higher abundance of disturbance-adapted species. There was less between-site variation in understory species assemblages in pine-oak forests experiencing pitch pine mortality and an increase in regeneration of pitch pine and scarlet oak in these areas. Collectively, the short-term results suggest SPB could functionally eliminate pitch pine from infested stands in the absence of additional management, and that management in pine-oak stands may exacerbate this trend, leading to increasing dominance of hardwoods species in pine barren communities. Based on our results, fuels reduction treatments combined with site-specific restoration of barrens structure and composition may be useful in maintaining stands with lower fire hazard and greater resilience to this new threat.
Keywords
Dendroctonus frontalis, Pinus rigida, Pine barrens, Long Island, Forest regeneration, Coarse woody debris
To read the full article please visit the link below:
Heuss, Molly, Anthony W. D’Arnato, and Kevin J. Dodds. 2019. “Northward Expansion of Southern Pine Beetle Generates Significant Alterations to Forest Structure and Composition of Globally Rare Pinus Rigida Forests.” Forest Ecology and Management 434 (February): 119–30. https://doi.org/10.1016/j.foreco.2018.12.015.
by Dr. Molly Darr | May 24, 2022 | 2011-2020 Publications, Southern Pine Beetle
Abstract
Southern pine beetle, Dendroctonus frontalis Zimmermann, is a major native pest of pine trees in the southeastern United States, Mexico, and Central America. The species’ range has recently expanded north for the first time in recorded history. Accordingly, information about the timing of population divergence and past geographic range occupancy may provide an important yardstick for understanding rapid range expansions. Using 16 new and eight existing microsatellite loci, together with mitochondrial (COI) and nuclear (EF-1α and 28S) DNA sequence data, we characterized broad-scale patterns of genetic variation in D. frontalis, and estimated divergence times for the entire D. frontalis species complex. Molecular dating suggested a middle Miocene (ca. 12 million years ago [Mya]) origin of the D. frontalis species complex, and an early Pleistocene (ca. 2.2 Mya) divergence between eastern and western D. frontalis populations that are separated by the Tamaulipan mezquital ecoregion in southern Texas and northeastern Mexico. In the western D. frontalis group, there was additional differentiation between populations from Michoacán versus Arizona, suggesting that additional genetic structure could be uncovered in this region. In the eastern group, there was high genetic diversity, but little structure. There was no pattern of isolation by distance, and only weak population differentiation that distinguished populations from Georgia and Florida from the other eastern populations. Overall, our results suggest that eastern D. frontalis originated as a distinct group well before the last glacial period, but additional markers may be necessary to fully describe its contemporary rapid range expansion.
Keywords
southern pine beetle, DNA sequence, genetic diversity, microsatellite, population genetics
To read the full article please visit the link below:
Havill, Nathan P., Anthony Cognato, Ek Del-Val, Robert J. Rabaglia, and Ryan Garrick. 2019. “New Molecular Tools for Dendroctonus Frontalis (Coleoptera: Curculionidae: Scolytinae) Reveal an East-West Genetic Subdivision of Early Pleistocene Origin.” Insect Systematics and Diversity 3 (2): ixz002. https://doi.org/10.1093/isd/ixz002.
