Variability in leaf traits,insect herbivory and herbivore performance within and among individuals of four broad-leaved tree species

Individual plants may vary in their suitability as hosts for insect herbivores. The adaptive deme formation hypothesis predicts that this variability will lead to the fine-scale adaptation of herbivorous insects to host individuals. We studied individual and temporal variation in the quality of leaves of the tree species ash, lime, common oak, and sycamore in the field as food for herbivores. We determined herbivore attack and leaf consumption and performance of the generalist caterpillars of Spodoptera littoralis in the laboratory. We further assessed the concentrations of carbon, nitrogen and water in the leaves.All measures of leaf tissue quality varied among and within individuals for all tree species. The level of herbivory differed among the tree individuals in lime, oak and sycamore, but not in ash. Within host individuals, differences in herbivory between the upper and lower crown layer varied in direction and magnitude depending on tree species. In feeding experiments, herbivore performance also varied among and within tree individuals. However, variation in palatability was not consistently related to the leaf traits measured or to herbivory levels in the field. The ranking of individuals with respect to the quality of leaf tissue for herbivorous insects varied between years in lime and oak. Thus, trees of both species might present moving targets for herbivores which prevents fine-scale adaptations. In contrast, among individuals of ash and sycamore the pattern of insect performance remained constant over 2 years. These species may be more suitable hosts for the formation of adapted demes in herbivores.     

Does insect herbivory on oak depend on the diversity of tree stands?

Studies on the effects of plant diversity on insect herbivory have produced conflicting results. Plant diversity has been reported to cause positive and negative responses of herbivores. Explanations for these conflicting responses include not only various population-level processes but also changes in plant quality that lead to changes in herbivore performance. In a tree diversity experiment, we investigated the effects of tree diversity on insect herbivory on oak in general and whether the effects of tree diversity on herbivore damage are reflected by the performance (leaf consumption, growth) of the generalist herbivore Lymantria dispar. Our study showed that the feeding damage caused by naturally occurring herbivores on oak trees decreased with increasing diversity of tree stands. The performance of L. dispar on oak leaves was not affected by tree diversity, neither in field nor laboratory experiments. Our results can be explained by the various processes behind the hypothesis of associational resistance.     

The role of leaf defensive traits in oaks on the preference and performance of a polyphagous herbivore,Orgyia vetusta

1. Leaves possess traits that mediate the preference and performance of herbivores. Most evidence for the importance of leaf traits as defences against herbivory comes from studies of few model plant species. 2. In a phylogenetically explicit comparison, I explain the differences in preference and performance of tussock moth (Orgyia vetusta Boisduval) larvae on leaves of 27 oak (Quercus) species using nine putative leaf defences. 3. The preference for an oak species correlated positively with the survival of caterpillars. The correlation between preference and performance did not differ between oak species native to the range of tussock moth versus those from outside the herbivore's range. 4. The first principal component of leaf traits predicted survival of caterpillars on oak leaves but only marginally predicted their preference between oak species. A multiple regression model showed that evergreenness, toughness, and condensed tannin content were the best predictors of caterpillar survival, and leaf toughness was the best predictor of host preference. 5. Generalist caterpillars may accurately assess the value of novel food sources. Moreover, many leaf traits that have been found to affect herbivory within a plant species can also be used to predict the fitness of a generalist herbivore between species.     

Herbivore attack in Casearia nitida influenced by plant ontogenetic variation in foliage quality and plant architecture

Traits influencing plant quality as food and/or shelter for herbivores may change during plant ontogeny, and as a consequence, influence the amount of herbivory that plants receive as they develop. In this study, differences in herbivore density and herbivory were evaluated for two ontogenetic stages of the tropical tree Casearia nitida. To assess plant ontogenetic differences in foliage quality as food for herbivores, nutritional and defensive traits were evaluated in saplings and reproductive trees. Predatory arthropods were quantified and the foraging preferences of a parasitoid wasp of the genus Zacremnops were assessed. In addition, survival rates of lepidopteran herbivores (Geometridae) were evaluated experimentally. Herbivore density was three times higher and herbivory was 66% greater in saplings than in reproductive trees. Accordingly, concentrations of total foliar phenolics were higher in reproductive trees than in saplings, whereas leaf toughness, water and nitrogen concentration did not vary between ontogenetic stages. Survival rates of lepidopteran larvae exposed to natural enemies were equivalent in reproductive trees and saplings. Given the greater herbivore density on saplings, equal survival rates implied a greater foraging effort of predators on reproductive trees. Furthermore, observed foraging of parasitoid wasps was restricted to reproductive trees. I propose that herbivore density, and as a consequence, leaf damage were lower in reproductive trees than in saplings due to both traits influencing food quality, and architectural or unmeasured indirect defensive traits influencing foraging preference of natural enemies of herbivores.     

Fluctuating asymmetry,leaf thickness and herbivory in <Emphasis Type="Italic">Tibouchina granulosa</Emphasis>: an altitudinal gradient analysis

Gradient of stressful conditions affect plant physiological and morphological traits. Previous studies have shown that plants located at higher altitudes might exhibit higher levels of both fluctuating asymmetry and leaf thickness. Although it is expected that higher fluctuating asymmetry levels should be accompanied by higher leaf consumption by herbivores, lower herbivory could be expected for elevated leaf thickness. Aiming to investigate this contradiction our objective was to determine the effects of altitude on fluctuating asymmetry and leaf thickness, and evaluate the importance of these two morphological traits on herbivory levels of Tibouchina granulosa Cogn. (Melastomatecea) in Brazilian Atlantic Forest. The study was conducted in southern Brazil, along a continuous altitudinal gradient raging from 1275 to 1950 m, where we measured fluctuating asymmetry, leaf thickness and herbivory from leaves of 29 individuals of T. granulosa. There was a positive effect of altitude on both fluctuating asymmetry and leaf thickness but only fluctuating asymmetry was related to herbivore. Our results suggest that as altitude increases plants face more stressful conditions, leading to higher fluctuating asymmetry. This may lead to a higher nutritional quality of leaves and herbivores may use leaf asymmetry as a cue for plant quality. The lack of a relationship between leaf thickness and herbivory gives us evidence that, in the studied location, leaf thickness is not primarily used as plant defense and probably has other functions related, for example, to water, solar radiation, and nutrient stresses. These results may be considered a baseline for the understanding on how altitudinal stress and potential herbivory pressure influence plant populations.     

Systemic induced resistance: a risk-spreading strategy in clonal plant networks?

Clonal plant networks consist of interconnected individuals (ramets) of different sizes and ages. They represent heterogeneous ramet assemblages with marked differences in quality and attractiveness for herbivores. Here, feeding preferences of a generalist herbivore (Spodoptera exigua) for differently-aged ramets of Trifolium repens were studied, and changes in herbivore preference in response to systemic defense induction were investigated. Dual-choice tests were used to assess the preference of herbivores for young versus mature ramets of induced and uninduced plants, respectively. Additionally, leaf traits related to nutrition, biomechanics and chemical defense were measured to explain variation in tissue quality and herbivore preference. Young ramets were heavily damaged in control plants. After systemic defense induction, damage on young ramets was greatly reduced, while damage on mature ramets increased slightly. Defense induction increased leaf strength and thickness, decreased leaf soluble carbohydrates and substantially changed phenolic composition of undamaged ramets connected to attacked individuals. Systemic induced resistance led to a more dispersed feeding pattern among ramets of different ages. It is proposed that inducible defense acts as a risk-spreading strategy in clonal plants by equalizing herbivore preference within the clone, thereby avoiding extended selective feeding on valuable plant tissues.     

Explaining differential herbivory in sun and shade: the case of Aristotelia chilensis saplings

Differential herbivory in contrasting environments is commonly explained by differences in plant traits. When several plant traits are considered, separate correlation analyses between herbivory and candidate traits are typically conducted. This makes it difficult to discern which trait best explain the herbivory patterns, or to avoid spurious inferences due to correlated characters. Aristotelia chilensis saplings sustain greater herbivory in shaded environments than in open habitats. We measured alkaloids, phenolics, trichomes, leaf thickness and water content in the same plants sampled for herbivory. We conducted a multiple regression analysis to estimate the relationship between herbivory and each plant trait accounting for the effect of correlated traits, thus identifying which trait(s) better explain(s) the differential herbivory on A. chilensis. We also estimated insect abundance in both light environments. Palatability bioassays tested whether leaf consumption by the main herbivore on A. chilensis was consistent with field herbivory patterns. Overall insect abundance was similar in open and shaded environments. While saplings in open environments had thicker leaves, lower leaf water content, and higher concentration of alkaloids and phenolics, no difference in trichome density was detected. The multiple regression analysis showed that leaf thickness was the only trait significantly associated with herbivory. Thicker leaves received less damage by herbivores. Sawfly larvae consumed more leaf tissue when fed on shade leaves. This result is consistent with field herbivory and, together with results of insect abundance, renders unlikely that the differential herbivory in A. chilensis was due to greater herbivory pressure in open habitats.     

Induced defences in the neotropical tree Bauhinia brevipes (Vog.) to herbivory: effects of damage-induced changes on leaf quality and insect attack

Induced defences to herbivory are physical, nutritional, and allelochemical traits that change in plants following damage or stress, and that reduce the performance and/or preference of herbivores. The aim of this study was to verify the occurrence and effect of induced responses in Bauhinia brevipes (Vog.) (Leguminosae) which defend it against herbivores, through the manipulation of its leaves, and their effects on herbivore foraging behaviour. We selected 15 plants in the field, and three shoots per plant were subjected to one of three treatments: (1) damaged shoots (simulation of the main types of foliar herbivory and insect exclusion); (2) damaged control shoots (insect exclusion); and (3) control shoots (not manipulated). Water and nitrogen content, tannin concentration, levels of herbivory, and shoot growth rates were compared among treatments. Leaf quality varied among treatments. Damaged leaves showed higher tannin concentration, and lower water and nitrogen content compared to undamaged leaves. On the other hand, they experienced higher rates of herbivory than leaves on control shoots. Moreover, shoots that were experimentally induced showed a higher increase in final shoot length. These results suggest that simulated herbivory on B. brevipes reduced the nutritional quality of its leaves and increased the amount of secondary compounds, therefore altering insect herbivore attack and increasing shoot performance.     

Interactions of root and leaf herbivores on purple loosestrife (<Emphasis Type="Italic">Lythrum salicaria</Emphasis>)

Interspecific interactions of herbivores sharing a host plant may be important in structuring herbivore communities. We investigated host plant-mediated interactions of root (Hylobius transversovittatus) and leaf herbivores (Galerucella calmariensis), released to control purple loosestrife (Lythrum salicaria) in North America, in field and potted plant experiments. In the potted plant experiments, leaf herbivory by G. calmariensis reduced H. transversovittatus larval survival (but not larval development) but did not affect oviposition preference. Root herbivory by H. transversovittatus did not affect either G. calmariensis fitness or oviposition preference. In field cage experiments, we found no evidence of interspecific competition between root and leaf herbivores over a 4-year period. Our data suggest that large populations of leaf beetles can negatively affect root-feeding larvae when high intensity of leaf damage results in partial or complete death of belowground tissue. Such events may be rare occurrences (or affected by experimental venue) since field data differed from data obtained from potted plant experiments, particularly at high leaf beetle densities. Interspecific interactions between G. calmariensis and H. transversovittatus are possible and may negatively affect either species, but this is unlikely to occur unless heavy feeding damage results in partial or complete plant death.     

Leaf quality and insect herbivory in model tropical plant communities after long-term exposure to elevated atmospheric CO2

Results from laboratory feeding experiments have shown that elevated atmospheric carbon dioxide can affect interactions between plants and insect herbivores, primarily through changes in leaf nutritional quality occurring at elevated CO₂. Very few data are available on insect herbivory in plant communities where insects can choose among species and positions in the canopy in which to feed. Our objectives were to determine the extent to which CO₂-induced changes in plant communities and leaf nutritional quality may affect herbivory at the level of the entire canopy. We introduced equivalent populations of fourth instar Spodoptera eridania, a lepidopteran generalist, to complex model ecosystems containing seven species of moist tropical plants maintained under low mineral nutrient supply. Larvae were allowed to feed freely for 14 days, by which time they had reached the seventh instar. Prior to larval introductions, plant communities had been continuously exposed to either 340 l CO₂ l^–1 or to 610 l CO₂ l^–1 for 1.5 years. No major shifts in leaf nutritional quality [concentrations of N, total non-structural carbohydrates (TNC), sugar, and starch; ratios of: C/N, TNC/N, sugar/N, starch/N; leaf toughness] were observed between CO₂ treatments for any of the species. Furthermore, no correlations were observed between these measures of leaf quality and leaf biomass consumption. Total leaf area and biomass of all plant communities were similar when caterpillars were introduced. However, leaf biomass of some species was slightly greater-and for other species slightly less (e.g. Cecropia peltata)-in communities exposed to elevated CO₂. Larvae showed the strongest preference for C. peltata leaves, the plant species that was least abundant in all communites, and fed relatively little on plants species which were more abundant. Thus, our results indicate that leaf tissue quality, as described by these parameters, is not necessarily affected by elevated CO₂ under relatively low nutrient conditions. Hence, the potential importance of CO₂-induced shifts in leaf nutritional quality, as determinants of herbivory, may be overestimated for many plant communities growing on nutrient-poor sites if estimates are based on traditional laboratory feeding studies. Finally, slight shifts in the abundance of leaf tissue of various species occurring under elevated CO₂ will probably not significantly affect herbivory by generalist insects. However, generalist insect herbivores appear to become more dependent on less-preferred plant species in cases where elevated CO₂ results in reduced availability of leaves of a favoured plant species, and this greater dependency may eventually affect insect populations adversely.     

Light environment and the impacts of foliage quality on herbivorous insect attack and bird predation

Theory predicts that variation in plant traits will modify both the direct interactions between plants and herbivores and the indirect impacts of predators of those herbivores. Light has strong effects on leaf quality, so the impacts of herbivores and predators may differ between plants grown in sun and shade. However, past experiments have often been unable to separate the effects of light environment on plant traits and herbivory from direct effects on herbivores and predators. We first manipulated light availability in an open habitat using a shade cloth pre-treatment to produce oak saplings with different leaf qualities. Leaves on plants exposed to high light were thicker and tougher and had lower nitrogen and water contents, and higher carbon and phenolic contents than leaves on plants under a shade cloth. Then, in the main experiment, we moved all plants to a common shade environment where bird predators were excluded in a factorial design. We measured insect herbivore abundance and leaf damage. Herbivores were significantly more abundant and caused greater leaf damage on sun trees, although these leaf characteristics are usually associated with low-quality food. Bird exclusion did not change herbivore abundance but did increase leaf damage. Contrary to our predictions, the effects of birds did not differ between trees grown in sun and shade conditions. Thus, differences in effects of predators on herbivores and plants between light habitats, when observed, might be due to variation in predator abundance and not bottom-up effects of host plant quality.     

Attracting pollinators and avoiding herbivores: insects influence plant traits within and across years

Perennial plants interact with herbivores and pollinators across multiple growing seasons, and thus may respond to herbivores and pollinators both within and across years. Joint effects of herbivores and pollinators influence plant traits, but while some of the potential interactions among herbivory, pollination, plant size, and plant reproductive traits have been well studied, others are poorly understood. This is particularly true for perennial plants where effects of herbivores and pollinators may manifest across years. Here, we describe two experiments addressing the reciprocal interactions of plant traits with herbivore damage and pollination across 2 years using the perennial plant Chamerion angustifolium. We measured (1) plant responses to manipulation of damage and pollination in the year of treatment and the subsequent season, (2) damage and pollination responses to manipulation of plant size and flowering traits in the year of treatment, and (3) plant-mediated indirect interactions between herbivores and pollinators. We found that plant traits had little effect on damage and pollination, but damage and pollination affected plant traits in both the treatment year and the subsequent year. We found evidence of indirect effects between leaf herbivores and pollinators in both directions; indirect effects of pollinators on leaf herbivores have not been previously demonstrated. Our results indicate that pollen receipt results in shorter plants with fewer stems but does not change flower number, while leaf herbivory results in taller plants with fewer flowers. Together, herbivory and pollination may contribute to intermediate plant height and plants with fewer stems and flowers in our system.     

Plant genotype and induced responses affect resistance to herbivores on evening primrose (Oenothera biennis)

Abstract. 1. Although both genotype and induced responses affect a plant's resistance to herbivores, little is known about their relative and interactive effects. This study examined how plant genotype of a native plant (Oenothera biennis) and induced plant responses to herbivory affect resistance to, and interactions among, several herbivores. 2. In a field experiment, genetic and environmental variation among habitats led to variation in the amount of early season damage and plant quality. The pattern of variation in early season infestation by spittlebugs (Philaenus spumarius, a piercing–sucking herbivore) negatively correlated with oviposition preference by a later feeding specialist weevil (Tyloderma foveolatum, a leaf‐chewer). 3. To determine if plant genotype and induced responses to herbivory might be responsible for these field patterns, we performed no‐choice and choice bioassays using four genotypes of O. biennis that varied in resistance. Plants were induced by either spittlebugs or weevils and assays measured the responses of the same specialist weevil as well as a generalist caterpillar (Spodoptera exigua). 4. Resistance to adult weevils was largely unaffected by plant genotype, while they experienced induced resistance following damage by conspecific weevils in no‐choice assays. Caterpillars were more strongly affected by plant genotype than induced responses in both no‐choice and choice assays, but they also fed less and experienced higher mortality on plants previously damaged by weevils. In contrast to the pattern suggested by the field experiment, spittlebugs did consistently induce resistance against either weevils or caterpillars in the bioassay experiment. 5. These results support recent findings that show herbivore species can compete via induced plant responses. Additionally, a quantitative review of the literature demonstrates that plant genotype tends to be more important than interspecific competition among herbivores (plant‐mediated or otherwise) in affecting herbivore preference and performance.     

Increased temperature alters feeding behavior of a generalist herbivore

Temperature can regulate a number of important biological processes and species interactions. For example, environmental temperature can alter insect herbivore consumption, growth and survivorship, suggesting that temperature‐driven impacts on herbivory could influence plant community composition or nutrient cycling. However, few studies to date have examined whether rising temperature influences herbivore preference and performance among multiple plant species, which often dictates their impact at the community level. Here, we assessed the effects of temperature on the performance and preference of the generalist herbivore Popillia japonica among nine plant species. We show that, on average, consumption rates and herbivore performance increased at higher temperatures. However, there was considerable variation among plant species with consumption and performance increasing on some plant species at higher temperatures but decreasing on others. Plant nutritional quality appeared to influence these patterns as beetles increased feeding on high‐nitrogen plants with increasing temperature, suggesting stronger nitrogen limitation. In addition to changes in feeding rates, feeding preferences of P. japonica shifted among temperatures, a pattern that was largely explained by differential deterrence of plant chemical extracts at different temperatures. In fact, temperature‐induced changes in the efficacy of plant chemical extracts led P. japonica to reduce its diet breadth at higher temperatures. Our results indicate that rising temperatures will influence herbivore feeding behavior by altering the importance of plant nutritional and chemical traits, suggesting that climate change will alter the strength and sign of plant–insect interactions.     

Inbreeding in horsenettle influences herbivore resistance

Abstract 1. Plant traits (e.g. nutrition, allelochemistry) are an important determinant of the feeding preferences and performance of insect herbivores. Recent evidence suggests that plant inbreeding can affect plant–insect interactions by impacting host‐plant quality and resistance to herbivory. 2. The effect of inbreeding on host‐plant quality for, and resistance against, the tobacco hornworm, Manduca sexta L., was assessed in the wild solanaceous weed horsenettle, Solanum carolinense L. Caterpillar preference, relative growth rate (RGR), total leaf consumption (TC), and per cent total nitrogen in leaves were examined using selfed and outcrossed progeny of eight maternal plants. 3. Inbreeding significantly influenced insect preference, with caterpillars preferring leaf discs from selfed versus outcrossed plants. There was also a breeding effect for RGR and TC, with both higher on selfed plants. No breeding effect for per cent total nitrogen was observed. 4. The results of this study indicate that inbreeding decreased resistance against the tobacco hornworm, but did not affect plant quality. Decreased plant resistance will likely alter interactions with the herbivore community and could also have important consequences for plant–herbivore–natural enemy interactions.     

Palatability, decomposition and insect herbivory: patterns in a successional old-field plant community

We tested the hypothesis that selective feeding by insect herbivores in an old‐field plant community induces a shift of community structure towards less palatable plant species with lower leaf and litter tissue quality and may therefore affect nutrient cycling. Leaf palatability of 20 herbaceous plant species which are common during the early successional stages of an old‐field plant community was assayed using the generalist herbivores Deroceras reticulatum (Mollusca: Agriolomacidae) and Acheta domesticus (Ensifera: Gryllidae). Palatability was positively correlated with nitrogen content, specific leaf area and water content of leaves and negatively correlated with leaf carbon content and leaf C/N‐ratio. Specific decomposition rates were assessed in a litter bag experiment. Decomposition was positively correlated with nitrogen content of litter, specific leaf area and water content of living leaves and negatively correlated with leaf C/N‐ratio. When using phylogentically independent contrasts the correlations between palatability and decomposition versus leaf and litter traits remained significant (except for specific leaf area) and may therefore reflect functional relationships. As palatability and decomposition show similar correlations to leaf and litter traits, the correlation between leaf palatability and litter decomposition rate was also significant, and this held even in a phylogenetically controlled analysis. This correlation highlights the possible effects of invertebrate herbivory on resource dynamics. In a two‐year experiment we reduced the density of above‐ground and below‐ground insect herbivores in an early successional old‐field community in a two‐factorial design by insecticide application. The palatability ranking of plants showed no relationship with the specific change of cover abundance of plants due to the reduction of above‐ or below‐ground herbivory. Thus, changes in the dominance structure as well as potentially associated changes in the resource dynamics are not the result of differences in palatability between plant species. This highlights fundamental differences between the effects of insect herbivory on ecosystems and published results from vertebrate‐grazing systems.     

Specificity of induced plant responses to specialist herbivores of the common milkweed Asclepias syriaca

Induced plant responses to herbivory appear to be universal, yet the degree to which they are specific to sets of herbivores is poorly understood. The generalist/specialist hypothesis predicts that generalist herbivores are more often negatively affected by host plant defenses, wheras specialists may be either unaffected by or attracted to these same "plant defenses". Therefore, specialists should be less predictable than generalists in their responses to induced plant resistance traits. To better understand the variation in plant responses to herbivore attack, and the impacts these responses have on specialist herbivores, we conducted a series of experiments examining pairwise interactinos between two specialaist herbivores of the common milkweed ( Asclepias syriaca ). We damaged plants mechnically, with swamp milkweed beetles ( Labidomera clivicollis ), or with monarchs ( Danaus plexippus ), and then asessed specificity of elicitation, both by measuring a putative defensive trait (latex volume) and by challenging plants with insects of both species in bioasays. Latex production increased by 34% and 13% following beetle and monarch herbivory, respectively, but only beetles significantly elevated latex production compared to undamaged controls. While beetle growth was negatively affected by latex across all experiments, beetles were not affected by previous damage caused by conspecifies or by monarchs. In contrast, monarchs feeding on previously damaged plants were 20% smaller, and their response was the same on plants damaged mechnically or by either herbivore. Therefore, these specialist herbivores exhibit both specificity of elicitation in plant responses and specificity of effects in response to prior damage.     

Leaf Colour as a Signal of Chemical Defence to Insect Herbivores in Wild Cabbage (Brassica oleracea)

Leaf colour has been proposed to signal levels of host defence to insect herbivores, but we lack data on herbivory, leaf colour and levels of defence for wild host populations necessary to test this hypothesis. Such a test requires measurements of leaf spectra as they would be sensed by herbivore visual systems, as well as simultaneous measurements of chemical defences and herbivore responses to leaf colour in natural host-herbivore populations. In a large-scale field survey of wild cabbage (Brassica oleracea) populations, we show that variation in leaf colour and brightness, measured according to herbivore spectral sensitivities, predicts both levels of chemical defences (glucosinolates) and abundance of specialist lepidopteran (Pieris rapae) and hemipteran (Brevicoryne brassicae) herbivores. In subsequent experiments, P. rapae larvae achieved faster growth and greater pupal mass when feeding on plants with bluer leaves, which contained lower levels of aliphatic glucosinolates. Glucosinolate-mediated effects on larval performance may thus contribute to the association between P. rapae herbivory and leaf colour observed in the field. However, preference tests found no evidence that adult butterflies selected host plants based on leaf coloration. In the field, B. brassicae abundance varied with leaf brightness but greenhouse experiments were unable to identify any effects of brightness on aphid preference or performance. Our findings suggest that although leaf colour reflects both levels of host defences and herbivore abundance in the field, the ability of herbivores to respond to colour signals may be limited, even in species where performance is correlated with leaf colour.     

Variations in leaf traits and susceptibility to insect herbivory within a Salix miyabeana population under field conditions

Variations in leaf traits (toughness, total nitrogen and total phenolic concentrations) and susceptibility to herbivory in Salix miyabeana were studied among individual trees within a population under field conditions. Leaf quality clearly decreased as season progressed, i.e. increases in leaf toughness and total phenolics and decrease in leaf nitrogen. Seasonal pattern and extent of herbivore attack were similar between years. Significant correlation between leaf traits and susceptibility to herbivore attack was detected, while effects of sex and plant size on leaf traits and herbivory were less clear. There was a negative correlation between total nitrogen and total phenolics, and a positive correlation between leaf toughness and total phenolics among trees. Trees with high quality leaves tended to suffer from frequent herbivore attack and leaf damage. Such a clear relationship between leaf traits and susceptibility to herbivory may be related with a life-history strategy of willows, which are rapid-growing pioneer species and generally respond to herbivorous damage not by induced resistance but by compensative growth. This revised version was published online in August 2006 with corrections to the Cover Date.