Mechanisms of Stress-induced Shifts in Leaf Beetle Resistance of Cottonwood

众所周知，非生物“胁迫”可能改变植物对昆虫的抗性，但对其机制知之甚少。最近的研究表明，单次急性环境剂量的臭氧会改变棉杨对昆虫和疾病的易感性。噬叶甲虫，花斑Plagiodera versicolora，受到的影响尤其严重。甲虫更喜欢以臭氧处理过的植物为食，消耗的植物比对照组多，但并没有更好地生长或生存；相对生长（每单位食物的生长）因此减少。雌性更喜欢在对照植物上产卵，与臭氧处理过的植物一起饲养时，繁殖力要低得多。臭氧也改变了棉杨树的化学成分。可溶性氮增加，酚苷减少，其他酚类物质聚合到细胞壁上。这些化学变化可能是“应激”引起的昆虫抗性变化的原因。研究了甲虫摄食和产卵偏好、消耗、相对生长和繁殖力变化的化学机制。化学分离与生物测定相结合；并将对特定化合物进行测试。还将确定甲虫对活性化合物的剂量反应，以及熏蒸后在植物中的时间过程。这些基础的、机械的研究也具有实用价值，因为它们将增加对空气污染对利用商业上重要物种的植物-昆虫相互作用的影响的认识。

It is well recognized that abiotic "stress" may change plant resistance to insects, but little is known about the mechanisms involved. Recent studies demonstrated that a single, acute, ambient dose of ozone changes susceptibility of cottonwood to insects and diseases. The leaf-chewing beetle, Plagiodera versicolora, is particularly affected. Beetles prefer to feed on and consume more of ozone-treated plants than controls, but do not grow or survive any better; relative growth (growth per unit food eaten) is therefore reduced. Females prefer to lay their eggs on control plants and have much lower fecundity when kept with ozone-treated plants. The chemistry of cottonwood plants is also changed by ozone. Soluble nitrogen increases, phenolic glycosides decrease and other phenolics become polymerized to cell walls. These chemical changes may be responsible for the "stress"-induced changes in insect resistance. The chemical mechanisms responsible for changes in beetle feeding and oviposition preference, consumption, relative growth and fecundity will be investigated. Chemical isolations combined with bioassays; and testing of specific compounds will be carried out. The dose response of the beetle to active compounds, and the time course in the plant following fumigation will also be determined. These basic, mechanistic studies also have a pragmatic value because they will increase knowledge of the effects of air pollution on plant-insect interactions using commercially important species.