The effects of foliage damage on casebearing moth larvae, Coleophora serratella, feeding on birch

ABSTRACT.

• 1 Mechanical damage to birch (Betula pendula Roth) leaves leads to an increase in the concentration of phenolic compounds, which spreads throughout the leaf within 8 days.
• 2 Coleophora serratella L. (Lepidoptera: Coleophoridae) apparently responds to this chemical change over a similar time scale. Within 24 h of pin-pricking leaves the casebearer moves from the immediate vicinity of the damage, but is just as likely to move to an undamaged portion of the damaged leaf as to vacate the leaf entirely. After 8 days mines on undamaged portions of damaged leaves were significantly smaller than mines on undamaged leaves.
• 3 Furthermore, Coleophora serratella reared on damaged trees took an average of 3 days longer to develop than those reared on undamaged trees.
• 4 It has been suggested that increased movement in response to damage-induced chemical changes causes hyperdispersed damage on plant foliage. Both within and between-leaf casebearer damage patterns were shown to be aggregated on birch.
• 5 Thus although mechanical damage can induce chemical and behavioural changes in the field, these are not reflected in the observed damaged patterns. We speculate on several possible reasons for this.

     

Comparison of Herbivores and Herbivory in the Canopy and Understory for Two Tropical Tree Species1

The Janzen–Connell model of tropical forest tree diversity predicts that seedlings and young trees growing close to conspecific adults should experience higher levels of damage and mortality from herbivorous insects, with the adult trees acting as either an attractant or source of the herbivores. Previous research in a seasonal forest showed that this pattern of distance‐dependent herbivory occurred in the early wet season during the peak of new leaf production. I hypothesized that distance‐dependent herbivory may occur at this time because the new foliage in the canopy attracts high numbers of herbivores that are limited to feeding on young leaves. As a consequence, seedlings and saplings growing close to these adults are more likely to be discovered and damaged by these herbivores. In the late wet season, when there is little leaf production in the canopy, leaf damage is spread more evenly throughout the forest and distance dependence disappears. I tested three predictions based on this hypothesis: (1) the same species of insect herbivores attack young and adult trees of a given plant species; (2) herbivore densities increase on adult trees during leaf production; and (3) herbivore densities in the understory rise during the course of the wet season. Censuses were conducted on adults and saplings of two tree species, raribea asterolepis and Alseis blackiana. Adults and saplings of both species had largely the same suite of chewing herbivore species. On adults of Q. asterolepis, the density of chewing herbivores increased 6–10 times during leaf production, but there was no increase in herbivore density on adults of A. blackiana. Herbivore densities increased 4.5 times on A. blackiana saplings and 8.9 times on Q. asterolepis saplings during the wet season, but there were no clear trends on the adults of either species. These results suggest that the potential of adult trees as a source of herbivores on saplings depends on the value of new leaves to a tree species' herbivores, which may differ across tree species.     

Effects of grafting on host plant resistance in ash (Fraxinus spp.) to emerald ash borer (Agrilus planipennis Fairmaire)

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Nitrate reduction and nitrate content in ash trees (Fraxinus excelsior L.): distribution between compartments,site comparison and seasonal variation

Summary Nitrate reductase activity (NRA), nitrate content and biomass components of leaflets, leaf stalks, old stem, current-year stem and roots of ash trees (Fraxinus excelsior L.) growing in their natural habitats were investigated. In addition, NRA, total nitrogen and nitrate concentration were analyzed in the leaves and roots of ash trees from four different field sites. The highest NRA per gram biomass and also per total compartment biomass was found in the leaflets, even though root biomass was much higher than total leaflet biomass. The highest nitrate concentrations were found in the leaf stalks. Correlations between nitrate availability in the soil and NRA in leaves were not significant due to high variability of the actual soil nitrate concentrations. The seasonal variation in foliar NRA, nitrate concentration and total nitrogen concentration is much smaller in F. excelsior than reported for herbaceous species and is mainly caused by changes in the actual soil nitrate availability and by senescence of the leaves.     

Frost damage and its cascading negative effects on <Emphasis Type="Italic">Aesculus</Emphasis><Emphasis Type="Italic">glabra</Emphasis>

Frost damage and re-foliation are seldom quantified for forest species, but are of ecological and evolutionary importance. This study of Aesculus glabra (Ohio buckeye) in a deciduous forest remnant in Illinois, USA, quantified frost damage to leaves and flowers after sub-freezing temperatures in April 2007. It also documented re-foliation and later growth, reproduction, and survival in 2007–2009 for the 355 study individuals of four life stages growing 0–200 m from the forest edge. Life stages differed in % leaf damage because of differences in phenology during the frost. Large saplings with fully expanded, immature leaves had higher % damage and lower % canopy fullness after re-foliation than smaller saplings with partially or fully mature leaves and canopy trees undergoing shoot expansion with folded leaflets. Percent damage increased for saplings closer to edges. Large saplings with heavier frost damage to leaves had partial re-foliation in deep shade, lower % canopy fullness, earlier senescence, a shorter growing season, and greater death of next year’s buds. By 2008, large saplings with greater damage in 2007 had more dead branches and lower % canopy fullness. By 2009, 11% of large saplings had died. In 2007, frost damaged no flowers, but final fruit crop size was negatively related to % leaf damage. Edge trees with total leaf damage aborted all fruits. The frost event differentially affected individuals in their length and time of growing season, energy budget, and, ultimately, reproduction, and survival. The population’s local-scale demography and spatial pattern also changed as large saplings died.     

Phenology and intensity of phyllophage attack on Fagus sylvatica in Wytham Woods, Oxford

ABSTRACT.

• 1 Overwintering beech buds began to swell in early April and bud-break occurred in early May. Most phyllophage attacks were initiated during the 21 day period of leaf growth but additional attacks occurred up to 46 days from bud break.
• 2 An average beech tree, with a top height of 24 m and a d.b.h. of 110 cm, bore 420 345 leaves (17% in the upper canopy, 27% in the upper middle canopy, 27% in the middle canopy, 18% in the lower middle canopy and 11% in the lower canopy).
• 3 Damage by phyllophages was greatest in the lower canopy; some 75—85% of the leaves were attacked in this stratum and damage amounted to 35% of the total phyllopage damage to the trees.
• 4 The major agents of damage in the lower canopy were adult P. argentatus, larval R. fagi and lepidopteran macrophages. Adult R. fagi concentrated their feeding in the upper canopy.
• 5 Allowing for damage expansion due to leaf growth the percentages of the total leaf area actually removed, or seriously damaged, by phyllophages were calculated to be 3.43–4.00% in 1978 and 2.37–2.74% in 1979.

     

Differential leaf traits of a neotropical tree Cariniana legalis (Mart.) Kuntze (Lecythidaceae): comparing saplings and emergent trees

Cariniana legalis is an emergent tree that reaches the upper canopy in Brazilian Semideciduous Forest. Spatial contrasts in microclimatic conditions between the upper canopy and understorey in a forest may affect morpho-physiological leaf traits. In order to test the hypothesis that the upper canopy is more stressful to leaves than a gap environment we compared emergent trees of C. legalis, 28–29 m in height to gap saplings, 6–9 m in height, for the following parameters: leaf area, leaf mass area (LMA the dry weight:leaf area ratio), leaf thickness, leaf anatomical parameters, stomata conductance, and chlorophyll a fluorescence. Leaves from emergent trees had smaller leaf areas but greater LMA compared to saplings. Leaf thickness, palisade layer thickness, and stomatal density were higher for emergent trees than for saplings. The opposite pattern was observed for spongy layer thickness and spongy/palisade ratio. Stomatal conductance was also higher for emergent tree leaves than for sapling leaves, but the magnitude of depression on stomatal conductance near midday was more pronounced in emergent trees. The potential quantum yield of photosystem II, as determined by the F _v/F _m ratio was lower for leaves from saplings. The lower values of stomatal conductance, indicating restriction in CO₂ diffusion into the mesophyll can be related to higher photoinhibition observed in the saplings. Leaves from emergent trees and saplings exhibited similar values for apparent electron transport rates and non-photochemical quenching. Our results suggest that changes in leaf traits could be associated to dry conditions at the upper canopy as well as to the ontogenetic transition between sapling/emergent tree life stages.     

Herbivore-induced resistance in Betula pendula: the role of plant vascular architecture

We studied the role of plant vascular architecture in the determination of the spatial extent of herbivore induced responses within Betula pendula Roth saplings. The induced responses were measured in bioassays in terms of the relative growth rate of larvae of a geometrid moth, Epirrita autumnata. We hypothesised that the level of induced resistance of a certain leaf would be determined by the degree of vascular connectivity between the leaf in question and a damaged leaf, as suggested by recent theoretical and empirical studies. A comparison of the control plants with the damaged plants indicated that damaging one leaf of a sapling was sufficient to induce an increase in the resistance level. There were also differences among the leaves within a plant in the resistance level, but these differences could not be explained by the degree of vascular connectivity with the damaged leaf. These results suggest that the vascular connections have low power as explanations of the spread and spatial extent of the induced resistance in Betula pendula saplings Instead, the resistance level of all leaves within a sapling increased following the damage. We suggest that the pattern of increased resistance observed in this experiment may be beneficial for the young saplings studied. For young saplings at their early stages of development, it may be beneficial to be able to distribute the induction signal to all leaves as fast as possible and thus repel the herbivore totally. For a young sapling, the capability of repelling the herbivore totally might thus be a feasible strategy whereas an older sapling may tolerate localised damage better and compensate for the damage within the undamaged plant parts.     

Short feeding period of carrot psyllid (Trioza apicalis) females at early growth stages of carrot reduces yield and causes leaf discolouration

Overwintered adult carrot psyllids [Trioza apicalis Förster (Homoptera: Psylloidea: Triozidae)] damage carrot [(Daucus carota ssp. sativum L.) (Apiaceae)] seedlings by phloem feeding on the leaves. The aim of this study was to investigate the carrot root and shoot growth in relation to carrot psyllid density during early growth stages. One, two, or three carrot psyllids were allowed to feed on carrot seedlings for 3 days. Leaf damage was measured at the 8‐leaf stage, and root, leaf fresh weight, and number of true leaves were measured at harvest. Both the age of the carrot seedling at infestation and the psyllid density had a significant effect on leaf damage at the 8‐leaf stage: seedlings damaged at the cotyledon stage exhibited more leaf damage than seedlings damaged at the 1‐leaf stage. A higher psyllid density significantly reduced the carrot root weight at harvest. The significant interaction of psyllid density with seedling age indicates that differently aged carrot seedlings responded differently to feeding: one psyllid feeding for 3 days at the cotyledon stage caused a significant yield loss, whereas three psyllids were needed to cause the same impact at the 1‐leaf stage. Carrot leaf weight at harvest was not reduced by carrot psyllid feeding: leaves recovered from the damage but roots did not. Our results confirm the farmers’ observations that a trap replacement period of 1 week for carrot psyllid monitoring is too long, especially at the cotyledon stage. Severe leaf discolouration on damaged carrots was observed at harvest. The possible reasons for this discolouration, such as toxin excreted in psyllid saliva or plant pathogenic mycoplasma infection, are discussed.     

Leaf damage effects on leaf expansion timing in Mallotus japonicus (Euphorbiaceae)

For many plant species, biotic factors determining the timing of leaf expansion have not been elucidated sufficiently. We investigated the effects of leaf damage on the timing of leaf defoliation and on the timing of leaf expansion in Mallotus japonicus (Euphorbiaceae). The degree of leaf herbivory of M. japonicus in the field was examined in summer, with subsequent investigation of the date of leaf defoliation in autumn and that of leaf expansion the following spring. Effects of artificial leaf damage on the timing of leaf defoliation and of leaf expansion were also examined in a greenhouse. In the field, the degree of leaf herbivory sustained by M. japonicus did not affect the timing of defoliation. However, the timing of leaf expansion the next spring advanced earlier, concomitantly with the increase of leaf damage during the previous year. Fifty per cent artificial leaf damage in M. japonicus saplings in summer had no marked effect on the timing of leaf defoliation in autumn. However, the effects of leaf damage on the timing of leaf expansion were apparent the following spring: the damaged plants expanded new leaves ca. 8 days earlier than control plants did. Plants that showed earlier leaf expansion tended to have a higher shoot/root ratio. Our results demonstrate that the plants advance the timing of their leaf expansion in response to leaf damage sustained during the previous year, suggesting that the shoot/root ratio is a determining factor.     

Physical,but not chemical,antiherbivore defense expression is related to the clustered spatial distribution of tropical trees in an Amazonian forest

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Compensation to simulated insect leaf herbivory in wild cotton (Gossypium hirsutum): responses to multiple levels of damage and associated traits

• Identifying the mechanisms of compensation to insect herbivory remains a major challenge in plant biology and evolutionary ecology. Most previous studies have addressed plant compensatory responses to one or two levels of insect herbivory, and the underlying traits mediating such responses remain elusive in many cases.
• We evaluated responses associated with compensation to multiple intensities of leaf damage (0% control, 10%, 25%, 50%, 75% of leaf area removed) by means of mechanical removal of foliar tissue and application of a caterpillar (Spodoptera exigua) oral secretions in 3‐month‐old wild cotton plants (Gossypium hirsutum). Four weeks post‐treatment, we measured plant growth and multiple traits associated with compensation, namely: changes in above‐ and belowground, biomass and the concentration of nutrients (nitrogen and phosphorus) and non‐structural carbon reserves (starch and soluble sugars) in roots, stems and leaves.
• We found that wild cotton fully compensated in terms of growth and biomass allocation when leaf damage was low (10%), whereas moderate (25%) to high leaf damage in some cases led to under‐compensation. Nonetheless, high levels of leaf removal (50% and 75%) in most cases did not cause further reductions in height and allocation to leaf and stem biomass relative to low and moderate damage. There were significant positive effects of leaf damage on P concentration in leaves and stems, but not roots, as well as a negative effect on soluble sugars in roots.
• These results indicate that wild cotton fully compensated for a low level of leaf damage but under‐compensated under moderate to high leaf damage, but can nonetheless sustain growth despite increasing losses to herbivory. Such responses were possibly mediated by a re‐allocation of carbohydrate reserves from roots to shoots.

     

Do warmer growing seasons ameliorate the recovery of mountain birches after winter moth outbreak?

Subarctic mountain birch (Betula pubescens ssp. czerepanovii) forests in northern Fennoscandia have shown a slight recovery from recent severe defoliation by the winter moth (Operophtera brumata). This development in trees is hypothesized to be a result of ameliorated growing conditions through increased summer temperatures. We examined if accumulated thermal sum affects the ability of mountain birches to tolerate foliage losses. We quantified the number of leaf-bearing short shoots, the emergence of inflorescences and the seasonal height growth of long shoots in both intact and defoliated trees. We also determined the concentrations of carbon and nitrogen in leaves and carbohydrates in roots. Our results show that defoliation constrained the growth of long shoots, as well as the emergence of inflorescences regardless of thermal sum accumulation. However, the number of leaf-bearing short shoots did not differ between intact and defoliated trees. In the both tree groups, the amounts of emerging leaves increased as a response to thermal sum accumulation. Also the leaf carbon concentration increased in defoliated trees at higher thermal sums, whereas it decreased in intact controls. Generally, the mean carbohydrate concentrations were greater in roots of defoliated than intact trees. However, with increased thermal sums, root carbohydrates increased in intact trees but remained the same in defoliated trees. We conclude that thermal sum accumulation does not greatly promote the recovery of mountain birches. Although the damaged trees produced more leaves at warmer growing sites, this did not increase their height growth or carbohydrate gain in roots.     

HETEROPHYLLY AND NEOFORMATION OF LEAVES IN SUGAR MAPLE (ACER SACCHARUM)

Variation in leaf form and timing of leaf initiation were investigated in vigorous leader shoots of open-grown saplings and larger forest trees of sugar maple (Acer saccharum Marsh.). Winter buds of leader shoots usually contained 6 or 8 leaf primordia and embryonic leaves, whereas 12 to 18 leaves typically expanded along the shoots each year. Preformed (early) leaves differ in form from neoformed (late) leaves. As in some other Acer species, the first-formed late leaves have large angles of secondary lobe divergence and deeply indented sinuses. This pattern of heterophylly contributes to the multilayered nature of open-grown saplings and leader shoots of forest trees of sugar maple.     

Observations on the Ecology of Weaver Ants (Oecophylla smaragdina Fabricius) in a Thai Mangrove Ecosystem and Their Effect on Herbivory of Rhizophora mucronata Lam.

Ants of the genus Oecophylla are predators of other insects and are able to protect a variety of terrestrial plants against pest insects; however, observations on the ecology of these ants in mangrove forests are lacking. General observations on the ecology of Oecophylla smaragdina were carried out in a Thai mangrove forest to determine if these ants can protect their host plants in less favorable mangrove habitats. Leaf herbivory and the density of O. smaragdina ants were measured on Rhizophora mucronata trees at two sites. The results showed a negative correlation between ant density and herbivory. At both sites, the mean percent damaged leaf area was more than four times higher on trees without ants compared to “ant‐trees.” A significant negative correlation was found between tree mean percent leaf damage and the density of ants on the tree. Furthermore, on trees with ants, there was less herbivory on leaves close to ant nests compared to other leaves on the tree. Most damage was caused by chrysomelid beetles (62%) and sesarmid crabs (25%) and both types of herbivory were significantly reduced on ant‐trees.     

Influence of previous frost damage on tree growth and insect herbivory of Eucalyptus globulus globulus

The plant stress hypothesis suggests that some herbivores favour stressed plants, whereas the plant vigour hypothesis proposes that other herbivores prefer vigorous plants. The effects of a prior stress, that of frost damage, were examined on the subsequent growth of Eucalyptus globulus globulus and on the response of insect herbivores. Frost damage affected tree growth by reducing new leaf area and increasing specific leaf area (SLA). However, herbivore abundance was not affected by prior frost damage. Two feeding trials using Anoplognathus chloropyrus and Hyalarcta huebneri and a morphometric study of Ctenarytaina eucalypti were conducted to assess the performance of herbivores on trees that had suffered more or less frost damage. Consumption by A. chloropyrus and H. huebneri was unaffected by foliage origin (damaged versus healthy). Hyalarcta huebneri grew faster when fed leaves from previously damaged trees, and C. eucalypti from previously damaged trees were larger than those from healthy trees. Enhanced insect performance on frost damaged plants may have resulted from the high specific leaf area (most likely thinner) leaves. The herbivore abundance data did not support the hypothesis that previously frost damaged plants are preferred by insects. However, increased growth of H. huebneri and larger body size of C. eucalypti on damaged trees indicates that previously stressed trees may produce leaves of higher nutritional value.     

Photosynthetic and biomass allocation responses of Liquidambar styraciflua (Hamamelidaceae) to vine competition

This 2-year field study examined stomatal conductance, photosynthesis, and biomass allocation of Liquidambar styraciflua saplings in response to below- and aboveground competition with the vines Lonicera japonica and Parthenocissus quinquefolia. Vine competition did not affect stomatal conductance of the host trees. The leaf photosynthetic capacity and photosynthetic nitrogen-use efficiency were significantly reduced by root competition with vines, either singly or in combination with aboveground competition, early in the second growing season. However, such differences disappeared by the end of the second growing season. Trees competing below ground with vines also had lower allocation to leaves compared with steins. Aboveground competition with vines resulted in reduced photosynthetic capacity per unit leaf area, but not per unit leaf weight, in trees. No correlation was found between single leaf photosynthetic capacity and tree growth. In contrast, a high positive correlation existed between allocation to leaves and diameter growth. Results from this study suggest that allocation patterns are more affected than leaf photosynthesis in trees competing with vines.     

Influence of soil gas contamination on tree root growth

Summary Rooted-cuttings and saplings of green ash (Fraxinus lanceolata) and hybrid poplar (Populus spp) were planted on a former municipal refuse landfill and on a nearby nonlandfill control plot. The root systems of four trees of each species and size were excavated on the landfill plot-two growing in an area where the concentrations of anaerobic landfill gases were relatively high and two in a relatively low-gas area. Two trees of each species and size were also excavated on the control. The root systems of both species were significantly shallower on the landfill plot than on the control. Green ash appeared to avoid the adverse gas environment of the deeper soil layers on the landfill by producing adventitious roots. Hybrid poplar became adapted in a different manner, by redirecting root growth from the deepter soil layers to the soil surface.     

Preference for plants damaged by conspecific larvae in ovipositing cabbage root flies: influence of stimuli from leaf surface and roots

In laboratory dual-choice assays females of the cabbage root fly, Delia radicum, prefer for oviposition plants with roots damaged by conspecific larvae to undamaged controls. Cauliflower and kale plants were inoculated with root fly eggs (25 per plant) and the hatching larvae were allowed to feed on the roots for various periods of time (1–17 days). After 4 (cauliflower) or 5 (kale) days of larval feeding the oviposition preference was most pronounced and flies laid between 64% and 68% of their eggs near plants with damaged roots. Later, with increasing damage but fewer surviving, and thus actively feeding, larvae, the magnitude of the preference declined. The preference for plants already damaged by conspecific larvae may contribute to the previously observed aggregated distribution of D. radicum eggs in Brassica crop fields.Further experiments revealed that the sensory cues inducing this oviposition preference originate from the complex consisting of the damaged roots, the surrounding substrate (soil) and associated microbes, rather than from the aerial plant parts. In choice assays using the root-substrate complex of damaged and control plants (aerial parts removed), the observed preference for damaged roots was similar to that found for the entire plant but was more pronounced. The damaged roots alone, compared to control roots, received up to 72% (cauliflower) and 75% (kale) of the eggs. By contrast, surrogate leaves sprayed with methanolic leaf surface extracts from the most preferred plants which had been damaged were not discriminated from surrogate leaved sprayed with extracts of the respective control plants. Analysis of glucosinolate levels in methanolic leaf surface extracts revealed that root damage resulted in enhanced concentrations of indole-glucosinolates on the leaf surface in kale but not in cauliflower. Although indole-glucosinolates are oviposition stimulants for the cabbage root fly, the induced changes were apparently too small to influence oviposition behaviour.     

Sequential patterns of colonization of coarse woody debris by Ips pini (Say) (Coleoptera: Scolytidae) following a major ice storm in Ontario

Abstract

• 1 It is widely known that many bark and wood‐boring beetle species use nonresistant coarse woody debris (CWD) created by disturbances; however, the ability of these secondary species to cause mortality in healthy trees following a build‐up of their populations remains unclear. We characterized the pattern of colonization by Ips pini (Say) following a major ice storm that created large amounts of CWD varying in resistance to colonization (i.e. ranging from snapped tops with no resistance to heavily damaged trees with intact root systems). A major question was how the beetles responded to the different types of storm‐damaged material and whether healthy undamaged trees were colonized and killed following increases in beetle populations.
• 2 Six red pine, Pinus resinosa Ait., plantations in eastern Ontario were monitored from 1998 to 2001 inclusive: three with high storm damage (approximately 120 m³/ha CWD) and three with minimal damage (approximately 20 m³/ha CWD). Transects (200 × 2 m) were sampled yearly in each plantation to assess the type and amount of damaged pine brood material colonized by the pine engraver beetle, I. pini.
• 3 Beetles preferentially infested the most nonresistant material available each year (i.e. all snapped tops in year 1, all standing snags, up‐rooted trees and many bent trees by year 2, but still less than 50% of trees blown over but with intact root systems by year 3). By years 3 and 4, the majority (approximately 75%) of severely damaged trees (with > 50% crown loss) died prior to beetle colonization.
• 4 The size of the beetle population tracked the abundance of available woody material from year‐to‐year within a plantation; populations were very large in the first 2 years, and declined significantly in the last 2 years.
• 5 Healthy standing red pines were apparently resistant to colonization by the beetles, despite the significant build‐up in their populations. Hence, the results of the present study suggest that native bark beetle populations will not cause further tree mortality following such a disturbance in this region.