Browsing by Subject "Dendroctonus simplex"

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    Biology and population dynamics of the eastern larch beetle, Dendroctonus simplex LeConte, and its interactions with eastern larch (tamarack), Larix laricina.
    (2015-09) McKee, Fraser
    The range of the eastern larch beetle, Dendroctonus simplex LeConte (Coleoptera: Scolytinae), is concomitant with its primary host, eastern larch (tamarack), Larix laricina (Du Roi) K. Koch, throughout the North American boreal forest. Since 2000, an ongoing outbreak of eastern larch beetles in the south-central part of tamarack’s range throughout the Great Lakes region has caused extensive mortality to mature tamaracks, affecting over 86,500 hectares of tamarack forest in Minnesota. Extended outbreaks in live trees are atypical of this insect, so the eastern larch beetle’s biology and ecology were studied under laboratory and field conditions in Minnesota from 2011 – 2014 to decipher the factors contributing to this ongoing outbreak. In the laboratory, the minimum and optimal developmental temperatures for eastern larch beetles were determined to be 7.5 and 27.9°C, respectively. Some progeny were able to reproduce in the absence of an overwintering period, suggesting that a reproductive diapause may not be obligate in all individuals. This was confirmed by field studies, which found that a second generation of eastern larch beetles successfully completed development during the summer and fall of 2012. Confirmation of two generations instead of three sibling broods established by re-emerging parents in one year was established by detailed phenological and physiological methods. As beetle infestations progressed through tamarack stands, beetles initially preferred to attack the largest tamaracks before killing smaller hosts at random in successive years. Reproductive success of females increased in larger and older tamaracks, and those “challenged” by unsuccessful attacks in the recent past. Higher concentrations of resin pockets within the phloem consistently reduced beetle reproduction. The size of male and female beetle offspring, as well as the total lipid content of female offspring, increased with tamarack size and phloem thickness. Development within “challenged” tamaracks reduced both the total and proportional lipid contents of all beetle offspring. New understandings of the population dynamics of eastern larch beetles are discussed. Expanding growing seasons, for example, may facilitate fractional voltinism, or, two generations in one year, among a portion of the population. Synchronous beetle emergence the following spring – shown in phenological studies – would enhance host procurement, especially of the largest and most preferred hosts that produce the most vigorous offspring, thus exacerbating the outbreak.
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    The resin defenses of eastern larch in response to eastern larch beetle: exploring insect-host dynamics under changing climatic conditions.
    (2024-07) Graham, Grace
    Dendroctonus bark beetles and conifers have coexisted in a dynamic equilibrium for millions of years. Although at times disrupting human goals for economic products, disturbances wrought by bark beetles are a critical component of forest successional dynamics. More recent anthropogenic impacts including climate change and the creation of vulnerable landscapes have increased the incidence and severity of bark beetle related tree mortality in North America beyond standard ecological parameters. One such example is an unprecedented outbreak of the native eastern larch beetle (ELB), Dendroctonus simplex LeConte (Coleoptera: Curculionidae; Scolytinae), in the eastern larch (tamarack), Larix laricina (Du Roi) K. Koch, forests of Minnesota. Warmer temperatures and extended growing seasons likely contributed to rapidly building numbers of ELB, resulting in a more aggressive population that attacks vigorous, large diameter trees. ELB have killed tamarack across 400,000 ha of forest in the state since 2001. An important driver of beetle-host interactions is tree defenses, especially resin, but little is known about these systems in tamarack. This work explores the defensive capacity of tamarack with a dendrochronological analysis of resin conducting networks visible in tree cores collected as part of foundational ELB research in 2011-2013, and an observational study of resin output repeated over the course of the growing season of 2023. Both studies illuminate a mismatch between the evolved defensive strategy of trees and current beetle population dynamics and address the limitations of current forest research and management models in a rapidly changing world.