Stratospheric ozone depletion and plant-insect interactions: Effects of UVB radiation of generalist and specialist herbivores on a tropical tree and a temperate forb

I investigated effects of UVB radiation on plant-insect interactions using two plant-herbivore systems.Treatment of Citrus jambhiri cuttings with elevated levels of UVB radiation ($\rm10\ kJ\ m\sp{-2}d\sp{-1}\ UVB\ BE\sb{300})$ increased the ratio of psoralen to bergapten in leaves. Furanocoumarin content varied according to leaf age. Phototoxicity of leaf extracts paralleled the furanocoumarin content of leaves. ANCOVA showed that leaf age-dependent phototoxicity could be accounted for on the basis of furanocoumarin content.Rooted C. jambhiri cuttings were grown at $\rm6.4\ kJ\ m\sp{-2}d\sp{-1}\ UVB.$ Furanocoumarins levels increased in irradiated plants and the increase of psoralen was greatest in young leaves. A generalist, Trichoplusia ni, was reared on artificial diets amended with furanocoumarins at ecologically relevant concentrations with and without supplemental UVB radiation. UVB radiation and dietary furanocoumarins caused severe mortality while furanocoumarins alone caused developmental delay with some treatment groups recovering from this delay in later development. Caterpillars reared on potted citrus cuttings under UVB radiation exhibited a similar developmental delay. Survivorship was also decreased.Using UVB levels of 6 and 12 kJ, I reared a specialist, Junonia coenia on excised leaves, potted plants, and artificial diet. No direct or indirect effects of UVB were observed on the development or survivorship of this specialist. A parallel set of experiments was conducted with the generalist. Elevated UVB radiation lowered the survivorship of T. ni reared on diet. Development of larvae reared on excised leaves was more rapid on young leaves from plants receiving enhanced UVB radiation. Caterpillars reared on potted plants developed more slowly when caterpillars were reared on plants growing at elevated UVB, indicating that the performance enhancing effects of UVB radiation seen in excised leaves were overridden in whole plants.Iridoid glycoside levels in Plantago lanceolata were unchanged but elevated UVB increased concentrations of verbascosides in young leaves. Allocation of above-ground biomass was altered; amounts of storage and reproductive biomass decreased when exposed to elevated UVB. Increasing herbivory was associated with decreased plant biomass.UVB decreased inflorescence number when plants were grown at 3.2 and 6.4 kJ.U of I OnlyETDs are only available to UIUC Users without author permissio