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山松甲虫抵御寄主树化学防御的能力和其幼虫的越冬成功。成年甲虫从育雏树上出来后，会寻找合适的寄主。在找到寄主后，成虫和它们的共生真菌通过信息素介导的大规模攻击克服了树的强大化学防御。虽然过去的许多研究都集中在容易接近的成年生命阶段，但对在树皮（韧皮部）内发育和越冬的隐生幼虫的研究很少。我实验室的研究表明，幼虫面临的挑战至少与它们的亲本在最初的寄主定居期间所面临的挑战一样多，这些挑战来自于寄主残余的、饱和韧皮部的防御性化学物质。有充分的理由相信，在这种有毒的环境中，早期幼虫的成功对冬季生存起着重要的作用。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冷冻保护剂，以在冬季温度下生存。因此，在孵化和冬季来临之间的短暂时间内，幼虫面临着从毒素饱和的韧皮部组织中获取足够能量的问题，同时也要维持能量密集型的生理过程，以便在数月的极端寒冷中生存。我们建议在山松甲虫幼虫孵化时遇到大量残留寄主树防御的背景下研究山松甲虫越冬生理。我们推测，秋季幼虫从防御性树脂浸泡韧皮部获取重要营养和能量的能力对其耐寒生理和最终越冬成功具有重要影响。我们将利用传统的野外研究以及多种基因组学方法来研究寄主毒素与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的预测模型，并为直接防治山松甲虫这种具有重要生态和经济意义的昆虫提供潜在目标。

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.