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.
