Population differences in Trifolium repens L-response to ultraviolet-B radiation: foliar chemistry and consequences for two lepidopteran herbivores

White clover growing in New Zealand is experiencing increasing levels of ul traviolet-B (W-B) radiation as a result of ozone depletion. We evaluated th e effects of UV-B radiation on the foliar chemistry of two populations of w hite clover (Trifolium repens L.), 'Huia' and 'Tienshan,' and the consequen ces for the performance of armyworms (Spodoptera litura) and cutworms (Grap hania mutans). Plants were grown in controlled environment rooms with and w ithout supplemental UV-B radiation at a dose of 13.3 kJ m(-2) day(-1), corr esponding to a 25% mid-summer ozone depletion above Palmerston North, New Z ealand. Tn both white clover populations, UV-B radiation elicited changes i n foliar chemistry, including slight increases in nitrogen concentrations a nd decreases in carbohydrate concentrations. In addition, the 'Huia' popula tion showed decreases in fiber concentrations and marked increases in cyano genic activity. No change in UV-absorbing compounds was detected in either population. Long- and short-term feeding trials were conducted to assess di etary effects on insect growth, consumption, and food utilization. Changes in the performance of both insect species were generally small. The most pr onounced effect was a 36% reduction in weight of S. litura after 2 weeks of feeding on Huia grown at high UV, but larval development times were only s lightly prolonged and pupal weights were unaffected. S. litura shortterm pe rformance was, affected by differences in white clover population. The long -term performance of G. mutans was not affected and its short-term performa nce (stadium duration and consumption rate) was only marginally affected by the high-UV treatment. We conclude that the effects of elevated W-B radiat ion on white clover plant chemistry can be specific to certain plant popula tions. The differences in sensitivity of the two generalist insect species suggest that effects may also be specific to certain plant-herbivore associ ations. These results indicate that future UV-B herbivory studies should ex amine genotypic effects in both plants and animals.