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

Abstract

We studied the effects of elevated ultraviolet-B radiation on interactions between insect herbivores and their host plants by exposing two species of phytochemically different willows, Salix myrsinifolia and S. phylicifolia, to a modulated increase in ultraviolet radiation in an outdoor experiment and monitoring the colonisation of insect herbivores on these willows. We examined the effect of increased ultraviolet-B (UV-B) radiation on (1) the quality of willow leaves, (2) the distribution and abundance of insect herbivores feeding on these willows, (3) the resulting amount of damage, and (4) the performance of insect larvae feeding on the exposed plant tissue. Six clones of each of the two willow species were grown in eight blocks for 12 weeks in the UV-B irradiation field. The clones were exposed to a constant 50% increase in UV-B radiation (simulating 20-25% ozone depletion), to a small increase in UV-A radiation or to ambient solar irradiation. We allowed colonisation on the willows by naturally occurring insects, but also introduced adults of a leaf beetle, Phratora vitellinae, a specialist herbivore on S. myrsinifolia. Increased UV-B radiation did not affect any of the measured indices of plant quality. However, numbers of P. vitellinae on S. myrsinifolia were higher in plants with UV-B treatment compared with UV-A and shade controls. In laboratory tests, growth of the second-instar larva of P. vitellinae was not affected by UV-B treatment of S. myrsinifolia, but was retarded on UV-B treated leaves of S. phylicifolia. In addition, naturally occurring insect herbivores were more abundant on willows exposed to elevated UV-B radiation compared to those grown under control treatments. In spite of the increased abundance of insect herbivores, willows treated with elevated UV-B did not suffer more herbivore damage than willows exposed to ambient solar radiation (shade control). The observed effects of UV-B on herbivore abundance, feeding and growth varied significantly due to spatial variation in environment quality, as indicated by the UV-treatment x block interaction. The results suggest that (1) environmental variation modifies the effects of UV-B radiation on plant-insect interactions and (2) specialist herbivores might be more sensitive to chemical changes in their secondary host plants (S. phylicifolia) than to changes in their primary hosts (S. myrsinifolia).

Effects of elevated ultraviolet-B radiation on a plant–herbivore interaction

“…An increase in UV-B radiation may trigger changes in the performance of a plant, an insect or in the interaction of the host plant species and its herbivore (e.g. Buck and Callaghan 1999;Gwynn-Jones 1999;Paul and Gwynn-Jones 2003;Veteli et al 2003). The responses to enhanced UV-B vary greatly between different plant-insect systems (e.g.…”

Innate and Introduced Resistance Traits in Genetically Modified Aspen Trees and Their Effect on Leaf Beetle Feeding

“…The reason for this lack of response is unclear but P. vitellinae has been found attracted by two related salicylate glucosides, tremulacin and salicortin [46] and none of these explained any significant part of the variation in secondary chemistry, only 0.65% in the latter case. In addition, tannin concentration, reported to have negative effect on P. vitellinae [22], [37], [38] had no influence at all on the difference in secondary chemistry between the Wt-clones. One likely reason for this is that young trees usually are high in glucosides and low in tannins [47], as was also the case in our study (Table 1).…”

“…Thus, induced levels of one important group of phenolic glucosides (salicylates) have shown little negative effect on feeding by the highly specialized P. vitellinae [34]–[36]. In contrast, they appear to avoid feeding on willow species with high tannin concentrations [33] and larvae of P. vitellinae grow less well on willows with high concentration of condensed tannins [22], [37], [38]. However, concentration of tannins was similar in the different lignin lines (4.2, 3.8 and 3.2% for COMT, CAD and Wt-Lignin, respectively) and differences in tannin concentration only explained 2.7% of the variation in secondary chemistry between lignin lines (Table 1).…”

Occurrence, development and economic importance of Phratora (= Phyllodecta) vitellinae (L.) (Coleoptera, Chrysomelidae)

“…Hallgren (2003 and dealt with the effect of the hybridization of S. caprea and S. repens L. on the concentration of secondary compounds in leaves and on insect herbivores (including P. vitellinae). Interactions between P. vitellinae and a primary host plant S. nigricans (or secondary host plant S. phylicifolia) and P. vitellinae in the environment with elevated UV radiation were studied by Veteli et al (2002). An increase in UV-B radiation did not affect any measurable characters of the food quality.…”

“…also P. vitellinae) can be more sensitive to secondary changes in secondary hosts than in primary hosts. Veteli et al (2002) dealt with the study of the effect of increased temperature and CO 2 concentration on the metabolism of S. nigricans and feeding of imagoes (including the growth of larvae) of P. vitellinae. With the increase of both climatic elements the above-ground biomass increased and the total concentration of phenolic substances in leaves decreased.…”