青藏高原高寒草甸门源草原毛虫取食偏好及其与植物C、N含量的关系

草食性昆虫对不同植物物种的取食存在偏好,这种取食偏好可能受其自身对蛋白质和碳水化合物的需求及二者平衡的调节。以青藏高原高寒矮嵩草草甸31种常见植物及门源草原毛虫为对象,通过饲喂实验,研究了草食性昆虫对不同物种和不同功能群植物的取食偏好,及其与植物叶片C、N含量和C∶N之间的关系。在31种植物中,门源草原毛虫对19种植物进行了取食,尤其对矮嵩草、红棕薹草、藏异燕麦和垂穗披碱草四种植物表现出强烈的取食偏好,而对另外12种植物未进行任何取食。在物种水平上,门源草原毛虫取食量与植物叶片N含量呈显著负相关,与叶片C∶N呈正相关。从功能群水平上看,门源草原毛虫对莎草类的取食偏好最大,而对豆科植物取食偏好最低;相应地,莎草类植物叶片N含量最低、C∶N最高,而豆科植物叶片N含量最高、C∶N最低。因此,即使在土壤有效氮匮乏、植物生长受氮素限制的高寒草甸生态系统,植物体内N含量的增加也可能不利于草食性昆虫的取食。门源草原毛虫对优势植物矮嵩草和垂穗披碱草的取食对高寒矮嵩草草甸物种共存和生物多样性维持可能具有重要的作用。     

Antibiosis/antixenosis in tulip tree and quaking aspen leaves against the polyphagous southern armyworm,Spodoptera eridania

Summary Previous studies have shown leaves of tulip tree, Liriodendron tulipifera L. (of the Magnoliaceae) and of Populus tremuloides Michx. (of the Salicaceae) to be antixenotic/antibiotic to many Lepidoptera, including one of the most polyphagous of all phytophagous insects, the southern armyworm, Spodoptera eridania Cramer (Noctuidae). We investigated the physiological responses to this phytochemical activity on neonate and late instar armyworm larvae in controlled environments with particular emphasis upon the leaf extracts containing condensed tannins and hydrolysable tannins. These tannin-containing extracts of tulip tree leaves and quaking aspen leaves were generally toxic to neonate larvae. For later instars, growth suppression was not due to digestibility-reduction, but instead to suppressed consumption rates and greatly increased metabolic (respiratory) costs as reflected in reduced biomass conversion efficiencies.     

Effects of nutrient and water stress on leaf phenolic content of peppers and susceptibility to generalist herbivoreHelicoverpa armigera (Hubner)

Pepper plants were grown under different water and nitrogen availabilities that produced severe nitrogen limitations and mild water stress. Nitrogen limitation produced lower leaf N content, higher C:N, and higher leaf content of phenolic compounds, in consonance with the carbon/nutrient balance hypothesis. Nitrogen limitation also produced lower nutritional quality of leaves, with lower relative growth rates and lower efficiency of conversion of ingested biomass on the polyphagous herbivoreHelicoverpa armigera. The biomass gained per gram nitrogen ingested also tended to be lower in those insects feeding on nitrogen-limited plants, in parallel with their higher phenolic content. However, larvae fed on nitrogen-limited plants did not increase the ingestion of food to compensate for the N deficiency of leaves. The mild water stress, which only slightly tended to increase the phenolic content of pepper leaves, had no significant effect on nutritional indices.     

Effects of variation in Eucalyptus essential oil yield on insect growth and grazing damage

Summary Levels of insect attack and yields of leaf essential oils in Eucalyptus vary widely within and among species. We tested the hypotheses that 1) metabolic cost of oil detoxification increases with increasing oil yield, resulting in lower herbivore growth rates and, consequently, 2) in lower herbivore damage to plants. Distribution of insect damage, eggs, immature insects and adults and feeding rates, growth and survivorship of insects do not support the hypotheses, although a threshold level of oil may be necessary to influence herbivorous insects. Herbivorous beetles tested do not detoxify essential oils. Levels of leaf nitrogen, rather than oil content, explained differences in insect feeding and growth.     

The role of leaf resin in the interaction between Eriodictyon californicum (Hydrophyllaceae) and its herbivore,Trirhabda diducta (Chrysomelidae)

Summary The chaparral shrub Eriodictyon californicum secretes a phenolic leaf resin composed of flavonoid aglycones. We used leaves with artificially altered resin contents to test the effects of resin on the feeding, growth, and oviposition of the specialist herbivore Trirhabda diducta. In addition, we compared Trirhabda feeding and growth on young foliage with that on foliage from the preceding year. Our results show that the Eriodictyon leaf resin affects Trirhabda larvae and adults similarly, having no significant effect on growth rates or on nutrient utilization at up to 5X the resin levels normally encountered by larvae in the field. Both Trirhabda larvae and adults respond to high resin concentrations by increasing their consumption rates, with concomitant decreases in digestibility and the efficiency of conversion of ingested food to biomass. Low-resin foliage is preferred by larvae for feeding and by adults for oviposition. Larvae feeding on leaves of the current season have higher growth efficiencies, consumption, and growth compared to larvae feeding on leaves from the preceding year.     

Leaf trait variation on Erythroxylum tortuosum (Erythroxylaceae) and its relationship with oviposition preference and stress by a host‐specific leaf miner

It has been suggested that plant physical and chemical traits vary considerably in space and time. Hence, leaf‐mining insects may adjust their oviposition in response to leaf attributes representing high quality. Moreover, herbivorous insects can modify leaf morphology by acting as stressors, increasing, for example, fluctuating asymmetry (FA) levels. Here, we investigate oviposition preference in Agnippe sp.2, a leaf‐mining moth of Erythroxylum tortuosum, in relation to differences in leaf nutritional quality (i.e. levels of water, nitrogen and tannin content), leaf area (i.e. quantity of resource hypothesis) and FA. We also verify whether temporal variation in plant nutritional quality emerges as an alternative hypothesis to explain oviposition distribution in time, and whether this leaf miner is a stress‐causing agent, increasing FA during larval development. Mined leaves and leaves with and without eggs were periodically collected from plants located in a Cerrado fragment in Brazil. In the laboratory, leaf traits were assessed (using image analysis software) and quantified (biochemical analysis) according to the aims previously determined. Oviposition probability did not change in relation to variations in nitrogen, tannins and FA of leaves. However, leaf‐miner females preferred to oviposit on leaves having large areas and low water contents. It was also verified that new leaves of E. tortuosum, which carried most leaf‐miner eggs, presented significantly lower tannins and greater levels of nitrogen and water than old leaves. The oviposition choice exhibited by leaf miners was found to be non‐random because they appear to use resource quantity and water content as cues as where to lay their eggs. The temporal variation of plant nutritional quality is likely to influence the time of leaf‐miner oviposition; and leaf FA was not increased during larval feeding, suggesting that these herbivores do not cause variations in FA levels.     

Leaf age effects of elevated CO2-grown white oak leaves on spring-feeding lepidopterans

Folivorous insect responses to elevated CO₂-grown tree species may be complicated by phytochemical changes as leaves age. For example, young expanding leaves in tree species may be less affected by enriched CO₂-alterations in leaf phytochemistry than older mature leaves due to shorter exposure times to elevated CO₂ atmospheres. This, in turn, could result in different effects on early vs. late instar larvae of herbivorous insects. To address this, seedlings of white oak (Quercus alba L.), grown in open-top chambers under ambient and elevated CO₂, were fed to two important early spring feeding herbivores; gypsy moth (Lymantria dispar L.), and forest tent caterpillar (Malacosoma disstria Hübner). Young, expanding leaves were presented to early instar larvae, and older fully expanded or mature leaves to late instar larvae. Young leaves had significantly lower leaf nitrogen content and significantly higher total nonstructural carbohydrate:nitrogen ratio as plant CO₂ concentration rose, while nonstructural carbohydrates and total carbon-based phenolics were unaffected by plant CO₂ treatment. These phytochemical changes contributed to a significant reduction in the growth rate of early instar gypsy moth larvae, while growth rates of forest tent caterpillar were unaffected. The differences in insect responses were attributed to an increase in the nitrogen utilization efficiency (NUE) of early instar forest tent caterpillar larvae feeding on elevated CO₂-grown leaves, while early instar gypsy moth larval NUE remained unchanged among the treatments. Later instar larvae of both insect species experienced larger reductions in foliage quality on elevated CO₂-grown leaves than earlier instars, as the carbohydrate:nitrogen ratio of leaves substantially increased. Despite this, neither insect species exhibited changes in growth or consumption rates between CO₂ treatments in the later instar. An increase in NUE was apparently responsible for offsetting reduced foliar nitrogen for the late instar larvae of both species.     

Responses of pest and non-pest Colias butterfly larvae to intraspecific variation in leaf nitrogen and water content

Summary This study examined the effects of intraspecific variation in leaf nitrogen and water content on the growth, consumption, conversion efficiency and nitrogen use of Colias butterfly larvae. Pest and non-pest Colias philodice eriphyle larvae and Colias eurytheme larvae were fed field-collected alfalfa (Medicago sativa) and vetch (Vicia americana) leaves in laboratory experiments. In all treatments, at least one indicator of larval growth performance was positively correlated with leaf nitrogen content, which supports the view that nitrogen is a limiting nutrient for larval growth. The benefits associated with eating leaves with high nitrogen content included higher growth rates, conversion efficiencies, nitrogen accumulation rates and larval nitrogen contents. Over the ranges examined in this study, variation in leaf nitrogen content (2.8–7.0% dry wt) affected larval growth more than variation in leaf water content (66–79% fresh wt). Pest and non-pest C. p. eriphyle responded alike to variation in the leaf nitrogen content of vetch, but there were differences between populations on alfalfa. Pest larvae were more sensitive to variation in leaf water content than non-pest larve. The differences between these populations may be due to specific adaptations resulting from the shift to alfala by pest Colias. It is suggested that herbivores' responses to intraspecific variation in leaf nitrogen content may have important consequences for the evolution of plant defenses and nutrient allocation patterns, and for agricultural pest management.     

The effects of elevated CO2 atmospheres on the nutritional quality of Eucalyptus foliage and its interaction with soil nutrient and light availability

 Seedlings of Eucalyptus tereticornis (Smith) were grown under two levels of availability each of CO₂ (352 and 793 μmol mol⁻¹), soil nutrients (1/24 and 1/4 Hoagland’s solution) and light (full and 30% sunlight). Low soil nutrient availability or high light increased the C:N ratio of leaves, leading to lower leaf nitrogen concentrations, higher leaf specific weights and higher levels of both total phenolics and condensed tannins. These results were consistent with other studies of the effect of environmental resource availability on foliage composition. Similar results were observed when the C:N ratio of leaves was increased under elevated CO₂. The changes in leaf chemistry induced by the treatments affected the performance of 4th-instar larvae of Chrysophtharta flaveola (Chapuis) fed on the leaves. Increased C:N ratios of leaves reduced digestive efficiencies and pupal body sizes and increased mortality. Below a threshold nitrogen concentration of approximately 1% dry mass, severe reductions in the performance of larvae were recorded. Such changes may have significant consequences for herbivores of Eucalyptus, particularly in view of projected increases in atmospheric CO₂. Received: 8 January 1996 / Accepted: 26 June 1996     

Limiting effects of low leaf-water content on the nitrogen utilization,energy budget,and larval growth ofHyalophora cecropia (Lepidoptera: Saturniidae)

Summary Hyalophora cecropia larvae were reared on leaves of wild cherry,Prunus serotina, which contained variable amounts of leaf water but otherwise did not differ in fiber, total nitrogen, and caloric content. Larvae which were fed leaves low in leaf water grew more slowly and were less efficient at utilizing plant biomass, energy, and nitrogen than those larvae fed leaves which were fully supplemented with water.Experiments were performed using excised leaves under different regimes of relative humidity and leaf water supplementation in climatic control chambers maintained at identical temperatures and photoperiod. Foodplant biomass utilization efficiencies were severely reduced by decreasing amounts of leaf water. Growth rates were halved and the efficiency of conversion of assimilated dry matter into larval biomass was reduced from 82% in the treatment with fully supplemented leaves to 34% in the driest treatment. The nitrogen utilization efficiency (N.U.E.) was reduced from 75–80% to 48%, and the relative accumulation rate of nitrogen (N.A.R.) was suppressed nearly 2-fold for larvae on low-water leaves. Relative maintenance costs (calories expended in respiration/mg tissue/day) of larvae were nearly five times higher on dry leaves than on fully supplemented leaves. Larvae on leaves which were low in water content were themselves more desiccated, and metabolized greater portions of assimilated energy, perhaps in an attempt to supplement body water with metabolic water derived from respiration.The larval rates of consumption of biomass, energy, and nitrogen were the same for all treatments, indicating that leaf water affected larval growth primarily by restricting the efficiency of utilizing these nutrients. Where water was limiting (as in tree leaves), an increased consumption rate did not appear to be a successful means of increasing growth rates. There were daily and seasonal differences in leaf water content between different trees of the same species. Although absolute differences in leaf water exist between different trees and between young and old (fully expanded) leaves of a single tree, these differences are proportional and parallel each other through daily and seasonal cycles.In spite of evolutionary adaptations of herbivores to acquire adequate water and avoid desiccation, the leaf water content naturally encountered by cecropia larvae on cherry leaves may limit their growth, especially if the R.H. is low.     

What physiological processes permit insects to eat Eucalyptus leaves?

Many species of insects eat Eucalyptus foliage despite its relatively low nutritional value and the many plant secondary metabolites (PSMs) present, for example, terpenes, phenols and formylated phloroglucinols (FPGs). Formylated phloroglucinols are a new class of PSMs that act as antifeedants for possums and koalas. What physiological processes are present that permit insects to eat eucalypt foliage and how do PSMs influence insect feeding or digestion? Some trees seem to be repeatedly infested with eucalypt‐feeding insects, possibly as a result of previous chemosensory cues remaining from parental selection of a plant. Avoidance or storage of PSMs permit jarrah leafminers (Perthida glyphopa) and sawflies (Perga sp.) to consume eucalypt foliage without dealing with the majority of these compounds. Some PSMs can be metabolized by polysubstrate membrane oxidases as found in caterpillars or sawflies that feed on eucalypts. High midgut pH may be advantageous for nutrient extraction and PSM metabolism, and midgut pH ranges between 8.5 and 8.9 for caterpillars of Hyalarcta huebneri. Plant secondary metabolites may not be absorbed as a result of the combined presence of the peritrophic matrix and endogenous surfactants. Excretion of PSMs can be as metabolites or intact compounds. Both putative metabolites and sideroxylonal‐A, an FPG, are present in the faeces of larvae of the case moth, H. huebneri. The presence of sideroxylonal‐A in the food had an effect on the presence of 5‐hydroxytryptamine (5HT) in the central nervous system of caterpillars, as larvae fed leaves with a high concentration of sideroxylonal‐A had relatively more 5HT in the brain and central nervous system ganglia than larvae fed leaves containing a low concentration. Further work is necessary to clarify how PSMs are handled by eucalypt‐feeding insects and what effect FPGs have on feeding and digestion.     

Variation in total phenols and condensed tannins in Eucalyptus: leaf phenology and insect grazing

Total phenols and condensed tannins in leaves of seven species of Eucalyptus ranged from 4–40% and 0–27% respectively of the leaf dry weight. The concentrations of these compounds were variable but usually high in young and older leaves throughout the growing season, and typically increased during winter, but no other trends with season or leafage were apparent. This pattern of seasonal variation in concentrations of total phenols and condensed tannins is different to that studied for other plant species. This difference may be related to repeated production of new leaves by Eucalyptus during the growing season, and the probability that these leaves will be attacked by herbivorous insects.     

Effects of increased water temperature on leaf litter quality and detritivore performance: a whole‐reach manipulative experiment

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Feeding responses of adapted and non-adapted insects to the defensive properties of Baccharis halimifolia L. (Compositae)

Summary Trirhabda bacharidis (Weber) (Chrysomelidae), a univoltine, monophagous beetle is the dominant herbivore on Baccharis halimifolia (Compositae), a woody, perennial shrub that leafs out in early spring and retains its leaves into November. Available plant biomass increases during the season but T. bacharidis feeds only during spring and early summer. During the remainder of the growing season, there are no major herbivores feeding on B. halimifolia. B. halimifolia leaves increase in toughness and thickness and decrease in moisture and nutrients as the season progresses. In feeding preference tests, T. bacharidis larvae preferred young leaves over leaves of older age classes. When reared on leaves of different ages, larvae fed on young leaves, weighed more, pupated earlier and had greater survivorship. T. bacharidis larvae showed no significant feeding preference for similarly tough B. halimifolia leaves painted with differing concentrations of late season acetone leaf extract. Elm leaves painted with the same leaf extracts were avoided by larvae of the non-adapted specialist Pyrrhalta luteola (Mueller) (Chrysomelidae).These results suggest that the adapted specialist, T. bacharidis, is not deterred by the B. halimifolia acetone soluble secondary chemical which increases in amount over the season. Decreasing leaf nitrogen (perhaps in concert with increasing leaf toughness) seems to be the primary factor that dissuades its feeding. However, acetone soluble secondary chemicals in the leaves of B. halimifolia may be effective in preventing herbivory from non-adapted insects.     

Growth responses of gypsy moth larvae to elevated CO2: the influence of methods of insect rearing

Abstract The effects of elevated CO₂ on foliar chemistry of two tree species (Populus pseudo‐simonii Kitag. and Betula platyphylla) and on growth of gypsy moth (Lymantria dispar L.) larvae were examined. Furthermore, we focused on the comparison of results on the growth responses of larvae obtained from two methods of insect rearing, the no‐choice feeding trial performed in the laboratory or in situ in open‐top chambers. On the whole, both primary and secondary metabolites in the leaves of the two tree species were significantly affected by main effects of time (sampling date), CO₂ and species. Elevated CO₂ significantly increased the C : N ratio and concentrations of the soluble sugar, starch, total nonstructural carbohydrates, total phenolics and condensed tannins, but significantly decreased the concentration of nitrogen. Higher contents of total phenolics and condensed tannins were detected in the frass of larvae reared in elevated CO₂ treatments. Overall, the growth of gypsy moth larvae were significantly inhibited by elevated CO₂ and CO₂‐induced changes in leaf quality. Our study did not indicate the two methods of insect rearing could influence the direction of effects of elevated CO₂ on the growth of individual insects; however, the magnitude of negative effects of elevated CO₂ on larval growth did differ between the two insect rearing methods, and it seems that the response magnitude was also mediated by larval age and host plant species.     

Intraspecific variation in aspen phytochemistry: effects on performance of gypsy moths and forest tent caterpillars

Individual quaking aspen trees vary greatly in foliar chemistry and susceptibility to defoliation by gypsy moths and forest tent caterpillars. To relate performance of these insects to differences in foliar chemistry, we reared larvac from egg hatch to pupation on leaves from different aspen trees and analyzed leaf samples for water, nitrogen, total nonstructural carbohydrates, phenolic glycosides, and condensed tannins. Larval performance varied markedly among trees. Pupal weights of both species were strongly and inversely related to phenolic glycoside concentrations. In addition, gypsy moth performance was positively related to condensed tannin concentrations, whereas forest tent caterpillar pupal weights were positively associated with leaf nitrogen concentrations. A subsequent study with larvae fed aspen leaves supplemented with the phenolic glycoside tremulacin confirmed that the compound reduces larval performance. Larvae exhibited increased stadium durations and decreased relative growth rates and food conversion efficiencies as dietary levels of tremulacin increased. Differences in performance were more pronounced for gypsy moths than for forest tent caterpillars. These results suggest that intraspecific variation in defensive chemistry may strongly mediate interactions between aspen, gypsy moths and forest tent caterpillars in the Great Lakes region, and may account for differential defoliation of aspen by these two insect species.     

Effects of leaf maturity and wind stress on the nutrition of the generalist caterpillar Lymantria dispar feeding on poplar

The growth rates of insect herbivores commonly decrease when they feed on mature leaves due to the combined effects of several nutritional and physiological mechanisms. Environmental stresses during leaf development may also decrease herbivore performance. The present study tests two main hypotheses to help clarify the importance of these factors for the nutrition and growth of an insect herbivore: (i) decreases in nutrient levels, consumption rates and nutrient assimilation efficiencies impact negatively on herbivores feeding on mature leaves and (ii) wind stress has a negative impact on herbivores feeding on mature leaves. The results show that mature poplar (Populus alba × Populus tremula) leaves have decreased levels of protein and increased levels of fibre, and that growth rates of gypsy moth (Lymantria dispar L.) are decreased on mature leaves in association with decreased consumption rates. However, in contrast to the first hypothesis, protein and carbohydrate are assimilated efficiently (74–82% and 84–87%, respectively) from immature and mature poplar leaves. The larvae are able to chew mature leaves as efficiently as immature leaves, potentially maximizing nutrient extraction. By contrast to the second hypothesis, wind‐stressed leaves have no significant detrimental effects on nutrient assimilation efficiencies, and the lower growth rates of L. dispar larvae feeding on mature wind‐stressed leaves can be explained by lower consumption rates. Therefore, the availability of nutrients to herbivores feeding on mature tree leaves is not necessarily impacted by lower assimilation efficiencies, even when leaves develop under wind stress. These results help explain some of the large variation between the nutritional qualities of trees for forest Lepidoptera.     

Changes in Clonal Poplar Leaf Chemistry Caused by Stem Galls Alter Herbivory and Leaf Litter Decomposition

Gall-inducing insects are highly specialized herbivores that modify the phenotype of their host plants. Beyond the direct manipulation of plant morphology and physiology in the immediate environment of the gall, there is also evidence of plant-mediated effects of gall-inducing insects on other species of the assemblages and ecosystem processes associated with the host plant. We analysed the impact of gall infestation by the aphid Pemphigus spirothecae on chemical leaf traits of clonal Lombardy poplars (Populus nigra var. italica) and the subsequent effects on intensity of herbivory and decomposition of leaves across five sites. We measured the herbivory of two feeding guilds: leaf-chewing insects that feed on the blade (e.g. caterpillars and sawfly larvae) and skeletonising insects that feed on the mesophyll of the leaves (e.g. larvae of beetles). Galled leaves had higher phenol (35%) and lower nitrogen and cholorophyll contents (35% respectively 37%) than non-galled leaves, and these differences were stronger in August than in June. Total herbivory intensity was 27% higher on galled than on non-galled leaves; damage by leaf chewers was on average 61% higher on gall infested leaves, whereas damage by skeletonising insects was on average 39% higher on non-galled leaves. After nine months the decomposition rate of galled leaf litter was 15% lower than that of non-galled leaf litter presumably because of the lower nitrogen content of the galled leaf litter. This indicated after-life effects of gall infestation on the decomposers. We found no evidence for galling x environment interactions.     

Nitrogen homeostasis in a willow leaf beetle, Plagiodera versicolora, is independent of host plant quality

While foliar nitrogen (N) content of host plants depends on environmental conditions, N content of herbivorous insects may remain relatively constant due to homeostasis. However, it is unknown to what extent insects can maintain their body elemental composition against natural variation in host plant quality. The present study examined the performance and N content of a willow leaf beetle, Plagiodera versicolora Laicharting (Coleoptera: Chrysomelidae), when fed leaves of host willow, Salix eriocarpa Franchet et Savatier (Salicaceae), with varying nutritional status. Water content, toughness, and N content of willow leaves varied seasonally, and they affected performance of the leaf beetle. The leaf beetle achieved high performance when fed young leaves. On the other hand, the N content of the leaf beetle changed little, and it was independent of that of willow leaves, indicating strong N homeostasis of the leaf beetle. We discussed the function of N homeostasis in herbivorous insects in tritrophic level interactions.     

Covariation of fluctuating asymmetry, herbivory and chemistry during birch leaf expansion

Fluctuating asymmetry (FA) is used to describe developmental instability in bilateral structures. In trees, high FA of leaves has been assumed to indicate the level of environmental or genetic stress, and for herbivores leaves from such trees have been shown to be in some cases (though not invariably) of higher quality compared to trees with symmetrical leaves. We demonstrated that FA of birch leaves correlated positively with growth rate of leaves, and with the amount of leaf biomass consumed by larvae of the geometrid Epirrita autumnata. Since asymmetry per se cannot define leaf quality for a herbivore, we determined the biochemical compounds which covary with the degree of foliage FA, in order to elucidate relationships between leaf FA, chemistry and herbivory. High foliar FA was characteristic of birches with high initial concentrations, and rapid seasonal decline in the concentrations of gallic acid and hydrolysable tannins, and with rapid seasonal changes in the concentrations of flavonoid-glycosides and sugars. In contrast, leaf FA was not related to concentrations of proanthocyanidins, protein-bound amino acids or soluble phenylalanine, the precursor of proanthocyanidins and proteins with aromatic amino acids. The positive correlation between leaf FA and consumption by E. autumnata was presumably related to the previously demonstrated compensatory consumption of E. autumnata to high concentrations of foliar gallotannins. Furthermore, sugars are well-known feeding stimulants. We propose that the variable results in studies correlating leaf FA and herbivory may stem from variable chemical associations of FA in different plants and of species-specific effects of compounds on insects. Received: 15 July 1999 / Accepted: 24 September 1999