Effects of enhanced UV‐B radiation on a weedy forb (Plantago lanceolata) and its interactions with a generalist and specialist herbivore

Abstract

AbstractAssessments of potential impacts of global climate change often focus exclusively on plants; however, as the base of most food webs, plants generally experience abiotic stresses concomitantly with biotic stresses. Longleaf plantain, Plantago lanceolata L., is a cosmopolitan temperate perennial weed that experiences a wide range of environmental conditions throughout its range. We examined the impacts of elevated levels of exposure to shortwave (UV‐B) radiation on this plant, on two herbivores associated with this plant, and on the plant‐herbivore interaction. Plantains were grown at 6 and 12 kJ m−2 d−1 BE300 UV‐B radiation and concentrations of iridoid glycosides (aucubin and catalpol), verbascosides, and nitrogen were measured. In terms of plant impacts, we found that iridoid glycoside concentrations were unchanged by elevated UV‐B radiation, whereas, in one experiment, the concentration of verbascosides in young leaves and levels of nitrogen in old leaves increased under elevated UV‐B radiation. Variation in plant chemistry due to leaf age and maternal family was greater than variation due to UV‐B exposure. When caterpillars were fed excised leaves from plants grown under elevated UV‐B, growth and survivorship of the specialist herbivore, Precis coenia Hbn. (Lepidoptera: Nymphalidae), were unaltered and growth of the generalist herbivore, Trichoplusia ni (Hbn.) (Lepidoptera: Noctuidae), was accelerated. When the caterpillars were reared on potted plants at high and low levels of UV‐B radiation, growth and survivorship of P. coenia were unchanged while growth of T. ni was significantly depressed by elevated UV‐B. Elevated UV‐B altered allocation patterns of above‐ground biomass in these plants; masses of crowns and reproductive tissue were reduced. UV‐B levels, however, did not affect distribution of damage to foliage inflicted by either species. In two additional experiments with artificial diet, designed to test the direct effect of UV‐B radiation on caterpillars, growth and survivorship of P. coenia were unaltered while survivorship of T. ni was significantly depressed when caterpillars were exposed to elevated UV‐B radiation. These studies collectively demonstrate that higher trophic level impacts of UV‐B‐induced changes in plants depend on the identity of the herbivore and its degree of adaptation not only to variation in hostplant quality but also variation in its light environment.