Effects of host tree chemical defenses on the overwintering physiology and success of mountain pine beetle larvae

影响山松甲虫种群增长的两个主要因素是它们对寄主树木化学防御的抵抗能力和幼虫的越冬成功率。从一棵树上出来后，成年甲虫会寻找一个合适的宿主。在找到宿主后，成虫和它们的共生真菌通过信息素介导的大规模攻击来克服树的强大化学防御。虽然过去的许多研究都集中在容易接近的成年生活阶段，很少有研究已经做了神秘的幼虫，因为他们发展和越冬的内树皮（韧皮部）。我实验室的研究表明，幼虫在最初的宿主殖民过程中，至少面临着来自宿主残留的防御化学物质的挑战，这些化学物质浸透了韧皮部。有充分的理由相信，早期幼虫在这种有毒环境中的成功在冬季生存中起着重要作用。在最近发表的一项关于越冬甲虫的研究中，我们已经表明，秋季幼虫必须解毒宿主的防御化学物质;它们积累应激生理蛋白;它们将能量用于生产甘油和其他防冻剂，以便在冬季温度下生存。因此，在孵化和冬季开始之间的短时间内，幼虫面临着从毒素饱和的韧皮组织获得足够的能量，同时也维持能量密集的生理过程，以便在极端寒冷的月份中生存。我们建议研究山松甲虫越冬生理的背景下，大量残留的主机树防御，幼虫孵化时遇到的。我们推测，秋季幼虫从防御树脂浸泡韧皮部获得重要营养物质和能量的能力对其耐寒生理和最终越冬成功有重大影响。我们将使用传统的实地研究沿着各种基因组学为基础的方法来调查宿主毒素和昆虫越冬生理之间的联系。本研究结果将有助于改进山松甲虫种群动态预测模型，并为直接控制这种具有重要生态和经济意义的昆虫提供潜在的目标。

Two major factors influencing mountain pine beetle population growth are their ability to withstand host tree chemical defenses and the overwintering success of their larvae. After emerging from a brood tree, adult beetles search for a suitable host. Upon finding the host, the adults and their symbiotic fungi overcome the tree's potent chemical defenses via a pheromone-mediated mass attack. While much past research has focused on the easily accessible adult life stage, very little research has been done on the cryptic larvae as they develop and overwinter in the inner bark (phloem). Research in my lab has shown that larvae face at least as much of a challenge from the host's residual defensive chemicals that saturate the phloem as did their parents during initial host colonization. There is good reason to believe that early larval success in this toxic environment plays an important role in winter survival. In a recently published study of overwintering beetles we have shown that autumn larvae must detoxify host defensive chemicals; that they accumulate stress physiology proteins; and that they devote energy to the production of glycerol and other cryoprotectants in order to survive winter temperatures. Thus, in the short time between hatching and the onset of winter, larvae are faced with obtaining sufficient energy from toxin-saturated phloem tissue while also maintaining energy-intensive physiological processes for survival during months of extreme cold. We propose to study mountain pine beetle overwintering physiology in the context of the substantial residual host tree defenses that the larvae encounter upon hatching. We hypothesize that the ability of autumn larvae to obtain vital nutrients and energy from defensive-resin soaked phloem has a major impact on their cold tolerance physiology and their ultimate overwintering success. We will use traditional field-based research along with a variety of genomics-based methods to investigate the connection between host toxins and insect overwintering physiology. Results of this work will help to improve predictive models for mountain pine beetle population dynamics and will provide potential targets for direct control of this ecologically and economically important insect.