Forest insect : a delicate balance between a primary and secondary insect

许多食草昆虫栖息在森林中，以树叶、树皮、木材、根、种子和其他植物部分为食。其中，树皮和木材钻孔昆虫主要利用内部树皮（韧皮部），形成层和木材（木质部）作为其食物资源。一般来说，大多数木质组织被认为是昆虫生长和发育的基质时，营养比叶组织差。因此，为了弥补这种营养不良的条件，一些种类的木蜂（Siricidae）在产卵时将Amylostereum真菌引入树木，然后腐烂木材并为发育中的幼虫提供营养，还有其他昆虫，如栖息在木材中的Ambrosia甲虫（Scolytidae），也开始完全依赖真菌作为食物来源。由于树皮和木材钻孔幼虫是无法退出的木本组织的宿主树木在发展过程中，他们最终的成年人的身体大小往往变化相当多，比自由生活的昆虫，由于高营养异质性的木本栖息地。在许多针叶树中，已知树脂是防御攻击活树的树皮甲虫和钻木虫的重要因素。因此，树皮和木材钻孔昆虫的发展和生存似乎密切受宿主树的条件，如营养水平和树脂流量。

Numerous plant-eating insects inhabit forests, feeding on leaves, bark, wood, roots, seeds and other plant parts. Among them, the bark- and wood-boring insects utilize mostly inner bark (phloem), cambium, and wood (xylem) as their food resources. In general, most woody tissues are nutritionally poorer than leaf tissue when considered as a substratum for insect g rowth and development. Hence, to compensate for such poor nutrient conditions, some species of woodwasps (Siricidae) introduced Amylostereum fungi into trees during oviposition, which then decays the wood and provide nutrients to the developing larvae, and still other insects such as ambrosia beetles (Scolytidae), which inhabit wood, had also come to depend solely on fungus as their source of food. Because bark- and wood-boring larvae are unable to exit the woody tissues of their host trees during development, their eventual adult body size often varies considerably more than free-living insects due to high nutritional heterogeneity in the woody habitat. In many coniferous trees, it is known that resin is an important factor for defense against bark beetles and wood-borers that attack living trees. Thus, development and survival of bark- and wood-boring insects appeared to be closely affected by host tree conditions such as nutrient levels and resin flow.