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

Abstract

White clover growing in New Zealand is experiencing increasing levels of ultraviolet-B (UV-B) radiation as a result of ozone depletion. We evaluated the effects of UV-B radiation on the foliar chemistry of two populations of white clover (Trifolium repens L.), 'Huia' and 'Tienshan,' and the consequences for the performance of armyworms (Spodoptera litura) and cutworms (Graphania mutans). Plants were grown in controlled environment rooms with and without supplemental UV-B radiation at a dose of 13.3 kJ m day, corresponding to a 25% mid-summer ozone depletion above Palmerston North, New Zealand. In both white clover populations, UV-B radiation elicited changes in foliar chemistry, including slight increases in nitrogen concentrations and decreases in carbohydrate concentrations. In addition, the 'Huia' population showed decreases in fiber concentrations and marked increases in cyanogenic activity. No change in UV-absorbing compounds was detected in either population. Long- and short-term feeding trials were conducted to assess dietary effects on insect growth, consumption, and food utilization. Changes in the performance of both insect species were generally small. The most pronounced 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 slightly prolonged and pupal weights were unaffected. S. litura short-term performance was affected by differences in white clover population. The long-term performance of G. mutans was not affected and its short-term performance (stadium duration and consumption rate) was only marginally affected by the high-UV treatment. We conclude that the effects of elevated UV-B radiation on white clover plant chemistry can be specific to certain plant populations. The differences in sensitivity of the two generalist insect species suggest that effects may also be specific to certain plant-herbivore associations. These results indicate that future UV-B herbivory studies should examine genotypic effects in both plants and animals.

UV exposure induces resistance against herbivorous insects in broccoli

“…The larvae of P. xylostella preferred plants from control conditions over plants from UV-conditions under artificial light, consumed less leaf material and fed more frequently but less leaf mass per feeding sequence on these plants, resulting in a lower pupal weight (Foggo et al 2007). Generally under high UV-conditions less feeding activity and lower weights of caterpillars and pupae from different lepidopteran species on several host plants could be confirmed outdoors under plastic-films with different UV-absorbing properties as well as indoors under UV-lamps, corroborating our findings (McCloud & Berenbaum 1999, Lindroth et al 2000. The UV-induced plant changes have the potential to influence herbivorous insects on the host plant in various ways.…”

Interactions between willows and insect herbivores under enhanced ultraviolet-B radiation

“…Although this should also have increased the LDI of willows treated with UV-B radiation, such was not the case. Nor, as suggested by the results of previous studies, did the increase in UV-B radiation decrease the amount of leaf damage (Hatcher and Paul 1994;BallarØ et al 1996;Rousseaux et al 1998;Lindroth et al 2000). Those studies indicate that UV-B improves the nutritive quality of host plants and thus reduces leaf consumption by insects, since the lesser amount consumed by the herbivore is enough to fulfil its nutritive demands (see e. g. Lindroth et al 1997).…”

“…Insect herbivores, when allowed to feed on leaves exposed to UV-B radiation, have shown altered patterns of growth, survivorship and feeding compared to insects feeding on leaves without exposure to UV-B (McCloud and Berenbaum 1999;Lindroth et al 2000). Only a few studies have been conducted in natural conditions.…”

Jasmonate-Dependent and -Independent Pathways Mediate Specific Effects of Solar Ultraviolet B Radiation on Leaf Phenolics and Antiherbivore Defense

“…The effects of UV-B on plant resistance to herbivory have been correlated with UV-B-induced variations in a number of tissue quality traits, including nitrogen content (Hatcher and Paul, 1994), leaf phenolics (McCloud and Berenbaum, 1994;Rousseaux et al, 2004;Izaguirre et al, 2007;Kuhlmann and Mü ller, 2009), cyanogenic compounds (Lindroth et al, 2000), and defense-related proteins such as proteinase inhibitors (Stratmann et al, 2000;Izaguirre et al, 2003;Stratmann, 2003). Increased accumulation of phenolic compounds is one of the best characterized responses to UV-B radiation; these compounds contribute to filter out UV-B photons before they reach sensitive molecules in the mesophyll (Braun and Tevini, 1993;Landry et al, 1995;Reuber et al, 1996;Bilger et al, 1997;Barnes et al, 2000;Mazza et al, 2000).…”