Trade-offs in the host selection by phloeophagous parasitic insects on conifers

昆虫和植物已经共存了数亿年，经常进化出密切的联系，甚至相互依赖。植物和昆虫之间最常见的相互作用涉及昆虫利用植物组织作为食物和/或繁殖资源，常常使昆虫与人类利益直接冲突。为了应对昆虫在木材中取食或繁殖所施加的选择压力，大多数木本植物都进化出了一种有效的防御化学物质。大多数种类的昆虫只能忍受有限的暴露于这些化学品，因此只能在死亡的宿主中进食和繁殖，但有限数量的物种可以利用活组织，或者在宿主死亡时入侵，杀死它，或者在少数情况下作为寄生虫生活。寄生昆虫对理解昆虫选择宿主的线索很感兴趣，这是我们仍然不太了解的。 宿主树抵御攻击的能力取决于它的活力和所使用的防御化学物质。如果树木的活力受到损害，例如，在干旱期间，树木的防御能力也会减弱，无论树木的化学防御多么好。由于昆虫幼虫不能离开不合适的宿主，它们母亲的错误最终将导致低生殖适合度。防御不力的树木往往会受到许多不同昆虫的攻击，导致激烈的竞争。因此，一只昆虫为寄主定向必须做出一连串的决定，包括在应对寄主防御或竞争之间进行权衡。如何做出这些选择是我研究计划的重点。 将对两种寄生在针叶树上的韧皮部取食物种进行研究。使用以场为中心的方法，包括谐波雷达跟踪昆虫和化学分析，以确定潜在的宿主抗性因素，我将研究昆虫使用什么线索，它们如何对它们作出反应，以做出最佳的宿主选择。结果将提供昆虫-植物相互作用的扩展知识，包括了解哪些因素有助于针叶树的抗性。

Insects and plants have co-existed for hundreds of millions of years, often evolving close associations and even co-dependence. The most common interaction between plants and insects involve the utilization of plant tissue as a food and/or breeding resource by insects, often placing insects in direct conflict with human interests. In response to the selective pressures exerted by insects feeding or breeding in wood, most woody plants have evolved a potent cocktail of defensive chemicals. Most species of insects can tolerate only limited exposure to such chemicals, and hence feed and breed only in dead hosts, but a limited number of species can utilize live tissue, either invading it as the host is dying, killing it, or in a few cases living as a parasite. The parasitic insects are of interest in understanding the cues that insects use in selecting a host, something we still don't understand very well. The ability of a host tree to defend itself against attack depends on both its vigour and the defensive chemicals used. If tree vigour is compromised, e.g., during droughts, the defensive ability of the tree will also be diminished, regardless of how well defended the tree is chemically. Since insect larvae cannot leave an unsuitable host, a mistake by their mother will ultimately result in low reproductive fitness. Poorly defended trees tend to get attacked by many different insects, leading to severe competition. Thus, an insect orienting a host must make a cascade of decisions, involving trade-offs between coping with host defense or competition. How these choices are made is the focus of my research program. Research will be conducted on two phloem feeding species that are parasitic on conifers. Using field-centred methods, including harmonic radar to track insects and chemical analyses to determine potential host resistance factors, I will examine what cues the insects use, how they respond to them to make an optimal host choice. The results will provide expanded knowledge of insect-plant interactions, including an understanding of what factors contribute to resistance in conifers.