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其抵御寄主树种化学防御的能力和其幼虫越冬的成功。成年甲虫从孵化树中出来后，会寻找合适的寄主。一旦找到寄主，成虫和它们的共生真菌就会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进入的成虫生活期，但对隐蔽的幼虫发育并在树皮内层(韧皮部)越冬的研究很少。我实验室的研究表明，幼虫面临的挑战至少与它们的父母在最初寄主殖民期间面临的挑战一样多，这些挑战来自寄主残留的防御性化学物质，这些化学物质饱和了韧皮部。有充分的理由相信，早期幼虫在这种有毒环境中的成功对冬季生存起着重要作用。在最近发表的一项关于越冬甲虫的研究中，我们表明，秋季幼虫必须为宿主的防御化学物质解毒；它们积累压力生理蛋白质；它们将能量用于生产甘油和其他低温保护剂，以便在冬季温度下生存。因此，在孵化和越冬之间的短时间内，幼虫面临着从毒素饱和的韧皮部组织中获得足够的能量，同时还要维持在极端寒冷的月份中生存所需的能量密集型生理过程。我们建议在幼虫孵化时遇到大量残留的寄主树防御的背景下，研究山松甲虫的越冬生理学。我们推测，秋季幼虫从防御性树脂浸泡的韧皮部中获取重要营养和能量的能力对它们的耐寒生理和最终的越冬成功具有重要影响。我们将使用传统的田间研究结合各种基于基因组学的方法来研究寄主毒素与昆虫越冬生理之间的联系。这项工作的结果将有助于改进山松甲虫种群动态的预测模型，并将为直接控制这一具有重要生态和经济意义的害虫提供潜在的靶标。

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.