Chlorogenic acid as an antiherbivore defence of willows against leaf beetles

In the leaves of 13 Finnish willow species, the content of a phenolic, chlorogenic acid, was found to vary from 0 up to 18 mg g^–1 D.W. Effects of pure chlorogenic acid on insect feeding behaviour were tested using four common leaf beetle species which are in the field mainly found on willows with low-chlorogenic acid leaves. One species, Lochmaea capreae L., was invariably deterred by pure chlorogenic acid applied in naturally occurring concentrations on the willow leaves. Accordingly, in 2-choice laboratory feeding trials L. capreae was found to prefer low-chlorogenic acid leaves of four willow species over high-chlorogenic acid leaves of Salix pentandra L. and S. myrsinifolia Salisb. When presented on the leaves of S. phylicifolia L, pure chlorogenic acid inhibited also the feeding by Phratora polaris Sp.-Schn. Instead, chlorogenic acid had no significant effect on Ph. polaris when it was presented on the leaves of another willow S. cinerea L. In laboratory, Ph. polaris did not show general preference for willow species with low chlorogenic acid content in their leaves. Thus, the response of Ph. polaris to chlorogenic acid seems to depend on the plant species. Apparently variation in other traits such as leaf hairyness may easily override the potential effect of chlorogenic acid content on Ph. polaris. To two other leaf beetle species, Galerucella lineola F. and Plagiodera versicolora Laich., chlorogenic acid is an ineffective deterrent even at unnaturally high concentrations. In laboratory, G. lineola and P. versicolora did not prefer willows with low chlorogenic acid content in their leaves. Thus, among four studied leaf beetle species, only L. capreae seems to be clearly affected by this phenolic. Therefore, overall importance of chlorogenic acid as a defence against willow-feeding leaf beetles appears to be very limited.     

Size class structure and tree dispersion patterns in old-growth cedar-hemlock forests of the northern Rocky Mountains (USA)

Summary The relationship between the food selection of four leaf beetle species (Phratora vitellinae, Plagiodera versicolora, Lochmaea capreae, Galerucella lineola) and the phenolic glycosides of willow (Salix spp.) leaves was tested in laboratory food choice experiments. Four willow species native to the study area (Eastern Finland) and four introduced, cultivated willows were tested.The willow species exhibited profound differences in their phenolic glycoside composition and total concentration. The food selection patterns of the leaf beetles followed closely the phenolic glycoside spectra of the willow species. Both the total amount and the composition of phenolic glycosides affected the feeding by the beetles. Phenolic glycosides apparently have both stimulatory and inhibitory influences on leaf beetle feeding depending on the degree of adaptation of a particular insect. Very rare glycosides or exceptional combination of several glycoside types seem to provide certain willow species with high level of resistance against most herbivorous insects. Analogously the average absolute amount of leaf beetle feeding was lower on the introduced willows than on the native species to which the local herbivores have a good opportunity to become adapted.     

The role of phenolic compounds and nutrients in determining food preference in greater snow geese

Summary We tested Buchsbaum's hypothesis that food palatability in geese is determined by a hierarchy of feeding cues among which deterrent secondary metabolites (mostly phenols) have a primary role (Buchsbaum et al. 1984). In preference tests, greater snow goose feeding was slightly depressed when grass was sprayed with ferulic acid but not when grass was sprayed with p-coumaric and tannic acids. Extracts of Timothy grass, red clover or alfalfa sprayed on grass also failed to depress goose feeding. In a multifactor experiment, phenol and protein content and height of grass were manipulated simultaneously. When ferulic acid was sprayed, protein and phenol content interacted in determining goose feeding preferences; protein content had no effect in the absence of phenol but did have an effect when phenol was added. When tannic acid was used in a similar experiment, results were inconclusive because of a significant and complex interaction between protein content and height of grass. Our results generally failed to support Buchsbaum's hypothesis that phenol content of plants has a primary role in determining food preference in geese. Protein content of plants seemed to be a more important factor.     

Host‐associated divergence in sympatric host races of the leaf beetle Lochmaea capreae: implications for local adaptation and reproductive isolation

Ecological specialization is widely recognized as a major determinant of the emergence and maintenance of biodiversity. We studied two critical facets of specialization – local adaptation and habitat choice – in the host races of the leaf beetle Lochmaea capreae on willow and birch. Our results revealed that there is asymmetric disruptive selection for host use traits, and host races achieved different adaptive sets of life history traits through association with their host plant. Beetles from each host race exhibited food and oviposition preference for their own host plant. Reciprocal transplant displayed significant variation in host acceptance and performance: all families from the willow race rejected the alternative host plant before initiation of feeding and all died on this host plant. By contrast, all families from the birch race accepted willow for feeding, but they consumed less and performed less well. Intriguingly, families that performed well on birch also performed well on willow, suggesting positive genetic correlation rather than genetic trade‐offs. Our results suggest that the major proximal determinant of host specialization in the willow race is the behavioural acceptance of a plant rather than the toxicity of the food resource. However, in the birch race a combination of behavioural host acceptance and performance may play a role in specialization. Our study sheds light on the mechanisms by which divergent host adaptation might influence the evolution of reproductive isolation between herbivorous populations.     

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.     

Ring-Tailed Lemur Home Ranges Correlate with Food Abundance and Nutritional Content at a Time of Environmental Stress

In order to determine whether ring-tailed lemurs (Lemur catta) adapt their ranging and select an optimal diet at a time of food shortage, we observed two adjacent troops in Berenty Reserve, Madagascar for over 250 h. The troops, created by a recent fission, ranged through closed canopy gallery forest next to a river and open forest away from the river. We conducted the study in September–October, 2000, normally a time of seasonally low resource availability, which was intensified by damage from a previous windstorm and recent drought. To examine the impact of environmental stress, we mapped their ranging patterns, intertroop encounters, feeding patches, siesta trees, and sleeping trees. We then correlated their ranging and feeding behavior with nutritional analyses of leaves and fruit from tamarind trees located in different parts of their ranges. One of the troops, D1A, ranged farther into open forest than previously. However, the range for troop D1B and the closed canopy portion of D1A's range were located in traditional positions for historical troops D and E. Both troops ate significantly more mature leaves from the tamarind trees in the closed canopy forest, where the leaves had significantly higher nutritional content (water and protein) than that of open forest samples. They fed on tamarind fruit significantly more often in the open forest away from the river, where it was more abundant. The lemurs selected a diet that maximized leaf water and protein and ranged where fruit was most abundant but at high energetic costs for troop D1A.     

Does Rust Infection of Willow Affect Feeding and Oviposition Behavior of Willow Leaf Beetles?

Willows are often attacked by both herbivorous insects and rust fungi. Little is known about interactions between these two willow enemies. We studied whether feeding and oviposition behavior of the willow leaf beetle Plagiodera versicolora upon the willow hybrid Salix x cuspidata is affected when the rust fungus Melampsora allii-fragilis has attacked the plant. Laboratory bioassays revealed that adult willow leaf beetles significantly avoided feeding and oviposition on rust-infected leaves when compared to healthy leaves. Further bioassays aimed to elucidate the temporal and spatial scale of effects of rust infection on feeding behavior of adults. While infected parts of leaves were avoided at all times past infection tested (8, 12, and 16 days), symptom-free parts of infected leaves were only avoided 16 days past infection. Systemic effects extended only one leaf position up and two leaf positions down from the infection site.     

Effects of leaf pubescence in Salix borealis on host- plant choice and feeding behaviour of the leaf beetle, Melasoma lapponica

Density of leaf trichomes in Salix borealis affected both the choice of individual host plants and feeding behaviour of adults and last instar larvae of the willow feeding leaf beetle, Melasoma lapponica. Beetles clearly preferred shaved disks to unshaved ones taken from the same leaf; this preference was highest in leaves of the most pubescent plants. High leaf pubescence explained the low preference for willow clones from the high density site in among-site preference trials; shaving significantly increased the consumption of these pubescent willow clones. In no-choice experiments, the food consumption by both adults and last instar larvae decreased with an increase in leaf pubescence. The time budget of adults did not depend on leaf pubescence of the host plants, however adults compelled to feed on highly pubescent plants changed their feeding sites twice as often as on less pubescent willow clones. Larvae feeding on highly pubescent plants spend moving three times as much time as larvae feeding on less pubescent plants. Combined with our earlier observations on the increase in leaf pubescence in the year(s) following defoliation, these data suggest that leaf hairiness may have contributed to the delayed induced resistance in S. borealis by disturbing the feeding behaviour of M. lapponica.     

The suitability of damaged willow leaves as food for the leaf beetle, Phgiodera versicolora

Abstract. 1. The effect of previous damage on the suitability of willow ( Mix bubylonicu and S.ulbu 'Tristis') leaves as food for the imported willow leaf beetle, Plugiodera versicoloru Laich. (Coleoptera: Chrysomelidae), was evaluated by feeding adults and larvae leaves from damaged and undamaged branchlets.
2. Females had lower fecundity when fed leaves from artificially damaged branchlets of S.ufba 'Tristis'. A similar result was obtained when beetles ate leaves from naturally damaged branchlets of S.babylonica .
3. Feeding preference tests suggest that the reductions in leaf suitability were not due to adults avoiding damaged leaves as a food source.
4. PZugiodera versicolora larvae required longer to develop and attained a lower adult weight when fed leaves from damaged branchlets.
5. Changes in leaf suitability brought about by herbivore feeding may affect the seasonal abundance of P.versicoloru on its willow hosts.     

Goose grazing selectivity along a depletion gradient

The micro-habilat food selectivity along a gradient of increasing grazing intensity of wintering pink-footed geese Anser brachyrhynchus and barnacle geese Branta leucopsis foraging on winter wheat Triticum aestivum and smooth meadow grass Poa pratensis was investigated. Protein content of ungrazed primary and secondary leaves of winter wheat did not differ, whereas the protein content of tertiary leaves was significantly lower. Secondary leaves were significantly longer than both primary and tertiary leaves, whereas tertiary leaves were significantly longer than primary leaves. Protein content of primary and secondary leaves of Poa pratensis did not differ, whereas the protein content of tertiary leaves was significantly lower. Primary leaves were significantly shorter than both secondary and tertiary leaves, which did not differ significantly.
For all leaf categories, there was an increase in the removal with increasing goose grazing intensity. The geese showed a sequential selection of winter wheat leaves according to the protein content, initially preferring primary and secondary leaves, but increasingly selecting tertiary leaves of poorer quality as high-quality leaves became depleted. Foraging on Poa pratensis. geese selected secondary leaves according to the protein content, whereas tertiary leaves were preferred to primary leaves, although these had a protein content equal to secondary leaves. This, however, may be explained by the primary leaves being too short to maintain intake rates.
It is concluded that feeding preferences cannot be established on the basis of protein contents of food plants alone and that green biomass estimates not necessarily reflect resource availability.     

The role of phenolic compounds and other plant constituents in feeding by Canada geese in a coastal marsh

Summary We have assessed the relative importance of phenolic compounds, other secondary metabolites, and gross nutrient levels as feeding cues to Canada geese. Phenolic content was the most significant constituent influencing feeding selection by geese. Nutrient content had little or no effect on feeding selection.Correlative data showing the negative influence of plant phenolics on food choices by wild geese were supported by feeding preference tests. Extracts of unpalatable plants inhibited feeding by captive geese relative to extracts of palatable plants. In high phenolic plants, the phenolic containing methanol extract was more inhibitory than extractions made with petroleum ether. In a relatively low phenolic, unpalatable plant, an inhibitory factor was extractable in petroleum ether, indicating that for this species, another class of deterrents was involved. Preference tests with individual secondary metabolites showed that tannic acid and quebracho tannin were very effective in inhibiting feeding by geese and phenolic acids were slightly inhibitory, but a sesquiterpene lactone was not deterrent. These results point out the primacy of some secondary metabolites in determining food choices by geese.     

The effects of willow and eucalypt leaves on feeding preference and growth of some Australian aquatic macroinvertebrates

The effect of leaf species (willow, Salix fragilis L., and white gum, Eucalyptus viminalis Labill.) and leaf state (senescent or green) on the feeding selectivity and growth rates of three species of macroinvertebrate Notalina sp. Mosely (Trichoptera: Leptoceridae), Koorrnonga sp. Campbell and Suter (Ephemeroptera: Leptophlebiidae) and Physastra gibbosa (Gould) (Mollusca: Planorbidae) were tested in the laboratory. All three species of macroinvertebrate selected green willow most strongly over the other leaf types (senescent willow, green eucalypt and senescent eucalypt). Growth rates of P. gibbosa and Notalina sp. were significantly greater on green willow than on the other leaf types. We were unable to measure the growth of Koorrnonga sp. Invertebrates had access to softer internal tissues of leaf material during preference trials, therefore we do not think that leaf structure was the main influence on selection between these materials. Green willow material may have been a better food source because of the noticeably thicker biofilm that it supported, and this material may also retain higher levels of nutrients than abscissed leaves. We speculate that willow leaves may provide a preferred source of food but will be available for less time than native eucalypt detritus.     

Seasonal Changes of the Antioxidative Systems in Foliar Buds and Leaves of Field-grown Beech Trees (Fagus sylvatica,L.) in a Stressful Climate

The activities of superoxide dismutase, ascorbate peroxidase, monodehydroascorbate radical reductase, and dehydroascorbate reductase and the contents of ascorbate, chlorophyll and soluble protein were determined in beech (Fagus sylvatica, L.) foliage over two or three seasons. Four important stages of leaf development were distinguished: resting buds, emerging, mature and senescent leaves. Foliar buds in spring, prior to the emergence of new leaves, contained a lower chlorophyll content but a higher protein content and higher activities of ascorbate peroxidase and monodehydroascorbate radical reductase than mature leaves in summer. By contrast, superoxide dismutase and glutathione reductase activities and ascorbate contents were higher in mature leaves than in swollen foliar buds. Dehydroascorbate reductase activity was low in all developmental stages. Resting buds in winter contained activities of superoxide dismutase, ascorbate peroxidase and monodehydroascorbate radical reductase that were similar to those found in mature leaves in summer, whereas the contents of total and reduced ascorbate were 6- and 20-times lower, respectively, in buds than in mature leaves. The low foliar concentration of reduced ascorbate in resting buds, despite high monodehydroascorbate radical reductase activity, suggests that the regeneration of ascorbate might be limited by the availability of reductant. High antioxidative capacity was conferred by mature beech leaves and may be an important protection measure for coping with the large fluctuations in temperature and exposure to elevated ozone concentrations in summer.     

Temperature and food quality influences feeding behavior,assimilation efficiency and growth rate of arctic woolly-bear caterpillars

Summary The energy budget for feeding activity and growth of larval Gynaephora groenlandica was investigated on the tundra and in the laboratory. Larvae fed only in June when the buds and young leaves of Salix arctica, its principal host plant, contained the highest concentrations of macro-nutrients and total nonstructural carbohydrates (TNC). The mid-summer hiatus in larval feeding was coincident with an abrupt decline in the TNC content of leaves and a buildup of plant secondary metabolites in the leaves of S. arctica. Following cessation of feeding, the larvae remained concealed from the sun within crevices and vegetation mats. Growth rates of larvae incubated at 15 and 30°C were similar (4.7–5.0 mg/larva/day), but the assimilation efficiency at 15°C was four times greater (40%) than at 30°C. Growth rates were lowest at 5°C (0.22mg/larva/day) as was the assimilation efficiency (6.6%), because of the extended residence time of food in the gut. The high rate of ingestion and excretion at 30°C was caused by elevated maintenance metabolism. Changes in metabolic state influenced oxygen consumption, which was highest for feeding larvae (0.29 ml/g/h) and significantly lower for each, digesting, moving, starved larvae, and lowest for inactive larvae (0.06 ml/g/h). An influence of temperature and leaf quality on digestion rate and maintenance metabolism is the most likely cause of the feeding behavior pattern in G. groenlandica. The larvae may undergo voluntary hypothermia in order to avoid an energy, deficit resulting from high maintenance metabolism during mid-season when the energy content and food quality declines. The restriction of growth and development to a very short period prior to mid-summer may have contributed, to the extended 14-year life cycle of this species.     

Feeding and ranging patterns of forest hanuman langurs (Presbytis entellus)

The feeding and ranging patterns of a troop of hanuman langurs (Presbytis entellus, Colobinae) were studied in Kanha Tiger Reserve, central Indian Highlands for 1850 hr (1981–1982), in a mosaic of moist deciduous forest and anthropogenic meadow. The location, size, and species of each tree within the 74.5-ha troop annual range was known and the phenology of all tree species was sampled. According to scan sampling, the troop spent 25.7% of the daytime feeding, with range use concentrated on an island of dry deciduous forest. Whereas adjacent troops occupied only the periphery of the focal troop's range, all-male bands occupied its center, especially during takeover and infanticidal attacks. The troop consumed items from 60 of the 67 species of trees and woody climbers available; mature leaves (34.9% of feeding time), fruits (24.4%), leaf buds (10.6%), flowers and flower buds (9.5%), young leaves (3.6%), insects (3.0%), and gum (1%). The monthly utilization of fruit, open leaf buds, and flower buds is correlated significantly with their abundance, and the troop spent significantly more time feeding and less time moving when consuming mature leaves. Comparison of tree dispersion and langur ranging patterns suggests that the distribution of the most important food trees is a major influence on their range use.     

Spatio-temporal abundance of flushing leaves shapes host selection in the willow leaf beetle, Plagiodera versicolora

In the willow leaf beetle, Plagiodera versicolora (Laicharting) (Coleoptera: Chrysomelidae), food resources available for adults are severely restricted by leaf toughness, which increases with age. Nevertheless, females require their own food almost all their life in order to produce eggs. In this paper, we have focused our attention on the spatio-temporal abundance of flushing leaves and have examined its effect on host-plant selection by adults among four co-occurring willow species ( Salix chaenomeloides , Salix eriocarpa , Salix integra , and Salix serissaefolia ) (Salicaceae) by field observations and experiments at two spatial scales. Among the various factors associated with this, the amount of new leaf production contributed maximally to variation in adult abundance. By conducting two experiments, we confirmed that the adults preferentially flew towards willow trees with abundant flushing leaves. Furthermore, we detected substantial seasonal changes in new leaf abundance and realized fecundity in the field, and a strong positive correlation was observed between them. Availability of adult food resources limited the reproductive performance of adults, particularly in mid-summer when only S. serissaefolia produced a few new leaves. These results supported the substantial effect of new leaf abundance on adult abundance in the field. Thus, we concluded that adult feeding is a critical factor that shapes the host-plant selection of P. versicolora and determines its seasonal occurrence through the dispersal and settlement of adults.     

Toughness and fiber content of major leaf foods of Japanese macaques (Macaca fuscata yakui) in Yakushima

During the spring, Japanese macaques in Yakushima feed predominantly on mature leaves of trees, vines, and ferns. They are selective in which parts of leaves they eat, and this study examines potential cues and consequences of typical patterns of selection. Toughness and fiber content (NDF) were assessed for 13 of the major leaf-food species from samples collected in the spring of 1994. The toughness of the petiole, the midrib, and two parts of the lamina were tested separately. Petioles were generally the toughest part of the leaf, followed by the midribs. For both midrib and lamina, there was a positive correlation between toughness and fiber content, but the toughness of midribs was at least three times that of laminae at similar fiber contents. A clear relationship was found between the toughness of plant parts and whether or not they were eaten: no plant parts with a toughness greater than 2,300 J m⁻² were consumed even at low fiber levels. Toughness therefore explained food selection patterns much better than did fiber content. Toughness is likely to be assessed at the front of the mouth or during mastication. However, the macaques rarely reject leaves after placing them in the mouth. We suggest, therefore, that toughness may be used to select between feeding sites, rather than between individual leaves. © 1996 Wiley-Liss, Inc.     

Herbivores and pathogens on willow: do they affect each other?

Abstract 1 Willows often need to cope with attack by both rust fungi and herbivores. We studied whether rust infection on willow affects the herbivore, and vice versa, whether herbivore feeding affects the fungal infection. The system investigated by laboratory bioassays and greenhouse experiments consisted of the willow hybrid Salix × cuspidata, the rust Melampsora allii‐fragilis and the willow leaf beetle Plagiodera versicolora. Effects were studied both on a local scale (rust infection and feeding on the same leaf) and systemically (rust infection and feeding on different, but adjacent leaves). 2 Rust infection was not affected by herbivore feeding on a local scale. Systemically, however, the willow's susceptibility towards rust infection was increased by herbivore feeding, as indicated by a higher number of rust sori on leaves adjacent to feeding‐damaged leaves. The herbivore's performance was detrimentally affected by rust infection: increase of mortality (systemically), decrease of larval weight (locally and systemically) and prolonging of developmental time (locally and systemically). 3 Previous rust infection enhanced systemically the willow's susceptibility towards subsequent fungal infection. Previous herbivore feeding on the willow had no effects on the herbivore's developmental time and mortality. However, feeding upon previously feeding‐damaged willow leaves significantly reduced larval weight.     

Dose-response effects of woody and herbaceous forage plants on in vitro ruminal methane and ammonia formation,and their short-term palatability in lactating cows

Plant secondary compounds (PSC) are prevalent in many woody, temperate-climate plant species and play a crucial role in dietary attempts to mitigate methane emissions in ruminants. However, their application requires sufficient palatability and feeding value. In the present study, leaves from silver birch (Betula pendula), hazel (Corylus avellana), blackcurrant (Ribes nigrum), green grape vine (Vitis vinifera) and the herbs rosebay willow (Epilobium angustifolium) and wood avens (Geum urbanum) were tested in various doses with the Hohenheim gas test method in vitro and their short-term palatability in dairy cows. For the palatability experiment, the plants were pelleted with lucerne in different proportions to obtain the same phenol content, but realised contents differed from expected contents. The pellets were provided separately from a mixed basal ration (0.4 : 0.6) to each cow, in a randomised order, for 3 days per plant. All plants mitigated in vitro methane and ammonia formation, often in a linear dose response. These levels of effects differed among plants. Significant effects were observed at 100 (hazel, rosebay willow) to 400 g/kg of plant material. The test plants had a lower feeding value than the high-quality basal diet. This was indicated by in vitro organic matter digestibility, short-chain fatty acid formation and calculated contents of net energy of lactation. Simultaneously, the linear depression of ammonia formation indicated a dose-dependent increase of utilisable CP. Only blackcurrant and birch were less preferred to lucerne. However, this aversion subsided on day 3 of offer. The rosebay willow pellets had the highest phenol content but were not the least palatable. Accordingly, PSC may not be the main determinants of palatability for the plants tested. Plants did not differ significantly in their short-term effects on milk yield and composition, and all of the plants substantially reduced milk urea content. Overall, the results suggest that hazel and vine leaves, and rosebay willow and wood avens herbs should be tested for their potential to mitigate methane and N emissions in vivo.     

Internal water balance of barley under soil moisture stress

Leaf water potential, leaf relative water content, and relative transpiration of barley were determined daily under greenhouse conditions at 3 growth stages: tillering to boot, boot to heading, and heading to maturity. The leaf moisture characteristic curve (relative water content versus leaf water potential) was the same for leaves of the same age growing in the same environment for the first 2 stages of growth, but shifted at the heading to maturity stage to higher leaf relative water content for a given leaf water potential. Growth chamber experiments showed that the leaf moisture characteristic curve was not the same for plants growing in different environments.

Relative transpiration data indicated that barley stomates closed at a water potential of about −22 bars at the 3 stages studied.

The water potential was measured for all the leaves on barley to determine the variation of water potential with leaf position. Leaf water potential increased basipetally with plant leaf position. In soil with a moisture content near field capacity a difference of about 16.5 bars was observed between the top and bottom leaves on the same plant, while in soil with a moisture content near the permanent wilting point the difference was only 5.6 bars between the same leaf positions.