Long-term dynamics of leaf miners, Eriocrania spp., on mountain birch: alternate year fluctuations and interaction with Epirrita autumnata

Abstract.

• 1 Abundance of leaf-mining larvae of the outbreak species Eriocrania spp. was monitored in northern Sweden in 1955–67 and 1984–92 in a mountain birch forest rejuvenated by an Epirrita autumnata outbreak in 1954–55.
• 2 Eriocrania mine density fluctuated in a regular biennial pattern, probably due to a semivoltine life cycle. The alternate year fluctuations had shifted phase between the two study periods.
• 3 The density fluctuated at a significantly higher mean level and with a lower amplitude in the c. 10-year-old forest in the 1960s than in the 30-year-old forest in the 1980s. However, no difference was found in mine density between c. 30- and >60-year-old stands in the 1980s.
• 4 Significant correlations between the density of mines in high-density years and date of budburst, and between rate of change between high-density years and the time between snow-melt and budburst indicate effects of weather. No correlation was found between yearly average mine density and date of budburst, precipitation or temperatures in May or June.
• 5 No correlation was found between the mean densities of Eriocrania mines and E.autumnata caterpillars in the same and the two preceding years. However, in the first (1955) and highest of three studied E.autumnata peaks a negative effect on population density of Eriocrania was indicated.
• 6 A significant, negative correlation between the number of Eriocrania mines and E.autumnata caterpillars on single branches was found in three out of eighteen years. The separation of caterpillars and mines at branch level indicates an effect of avoidance at intermediate population densities.

     

Decomposition and macroinvertebrate colonization of aquatic and terrestrial leaf material in alkaline and acid still water

• 1 Decomposition of the leaves of Nymphaea alba L. and Betula pubescens Ehrh. was studied in two ponds of contrasting pH, buffering capacity and trophic level. Rates of carbon loss, concentrations of nitrogen, protein and phenolics and colonization of the leaf material by macroinvertebrates were studied.
• 2 Decomposition of B. pubescens leaves was slower than that of N. alba in both ponds. Protein and phenolic concentrations were higher in the decomposing N. alba material, whereas no significant difference was found for nitrogen concentrations.
• 3 Decomposition of both species was slower in the acid water. The effect of acid water on decomposition rate was similar for both species. Both nitrogen and protein concentrations of N. alba remained higher under acid conditions, whereas no effect of study site was observed on the protein and nitrogen concentrations in B. pubescens litter. The concentration of phenolic compounds was higher in N. alba litter from the acid pond; no such difference was observed for B. pubescens litter. The high concentrations of phenolic compounds in N. alba litter from the acid pond probably induced chemical immobilization (tanning reaction), yielding high concentrations of nitrogen and protein in the litter.
• 4 Diversity of the detritivorous macroinvertebrate fauna on the litter of both species was extremely low in the acid pond, while a relatively high diversity occurred in the alkaline water. Exclusion of large macrofauna inhibited decomposition in the alkaline water, while there was no comparable influence in the acid water.
• 5 The effects of low pH on the decomposition of both terrestrial and aquatic macrophyte litter appeared to be caused by interactive effects of low pH on the microbial decomposition, on the detritivorous macroinvertebrates and, in the case of N. alba, on the resource quality of the detritus.

     

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.

     

Behavioural responses of the leaf-chewing guild to the presence of Eriocrania mines on silver birch (Betulapendula)

1. Interactions between early season leaf-miners from the genus Eriocrania Zeller (Eriocraniidae: Lepidoptera), and the leaf-chewing guild of silver birch (Betula pendula Roth) were investigated. 2. Field observations indicated that a negative association between damage caused by Eriocrania, and leaf-chewers could be observed under certain conditions, namely at higher damage densities in the final week of mine development on trees with relatively high densities of mines. 3. Experimental manipulation of Operophtera brumata L. (Geometridae: Lepidoptera) densities in the field confirmed the negative association between established mines of Eriocrania, and this species of free-living folivore. 4. The behaviour of O. brumata was modified further in the presence of mines. On branches where mined leaves were present, O. brumata larvae consumed a larger proportion of leaf tissue, by continuing to feed on the same leaf longer rather than shifting to a new leaf. Increased consumption may indicate some modification of leaf quality beyond the leaves occupied by Eriocrania. Alternatively, it may indicate an association between Eriocrania, and higher quality leaf material.     

Foliar damage, parasitoids and indirect competition: a test using herbivores of birch

ABSTRACT.

• 1 The hypothesis that leaf-chewing caterpillars and leaf miners indirectly compete via the influence of foliar damage on parasitoids was experimentally tested using the leaf miner Coleophora serratella (L.) and a complex of folivorous caterpillars on birch.
• 2 Separate experiments tested the effects of manipulating artificial or caterpillar-induced leaf damage on parasitism of leaf miners at several spatial scales.
• 3 Parasitism of C. serratella by specialist and generalist parasitoids was independent of the extent of either collateral or leaf-miner damage, whether experimentally or naturally induced.
• 4 Support in the literature for the hypothesis is restricted to a single case, and only on a limited spatial scale; thus, the idea that collateral damage directs parasitoid-mediated competition among herbivores remains highly speculative.

     

Differential resource utilization and co-occurrence of leaf miners on oak (Quercus dentata)

Abstract.

• 1 Spatial, temporal, and dietary differences in resource utilization and patterns of interspecific association on leaves were investigated for dominant and common leaf-mining species on an oak species, Quercus dentata Thunb., in Hokkaido, northern Japan.
• 2 Leaf miners were divided into two groups according to leaf tissues used for food: upper-layer-feeders which consume the palisade paren-chymatous layer (Stigrnella spp. and tenthredinid sp.), and full-depth-feeders which consume spongy and palisade parenchymatous layers (Phyllonorycter leucocorona (Kumata), P.similis Kumata, and Caloptilia sapporella (Matsumura)).
• 3 Differences in the position of mines on leaves were found among species: mines of P.similis were distributed more frequently in the middle section of leaves, whereas those of the remaining species were concentrated in the basal section.
• 4 Leaf size preference differed between species: C.sapporella and tenthredinid sp. tended to select larger leaves more frequently than did the other species.
• 5 Phenological differentiation was found among species: C.sapporella appeared earliest, followed by P.similis, P.leucocorona and a tenthredinid sp., and then Stigmella spp.
• 6 Each species showed a highly clumped distribution among leaves. Leaf miners of some species pairs co-occurred on leaves more frequently than expected by chance.

     

Oviposition preference and neonate performance of Mnesampela privata in relation to heterophylly in Eucalyptus dunnii and E. globulus

Abstract

• 1 The autumn gum moth, Mnesampela privata, is an endemic Australian geometrid that utilizes a number of species within the genus Eucalyptus as hosts. Based on field observations, the moth is thought to be leaf‐type specific for juvenile as opposed to adult eucalypt foliage.
• 2 Laboratory binary choice assays of the oviposition preference of host novice M. privata confirmed that eggs were more likely to be laid upon juvenile rather than adult foliage of Eucalyptus dunnii and two subspecies of E. globulus. This oviposition preference was not influenced by differences in leaf size or adherence to leaves by ovipositing moths. The high specific leaf weights common to adult leaves were associated with reduced oviposition.
• 3 Although neonates fed on both juvenile and adult leaves of most of the trees studied, performance was greater on juvenile as opposed to adult foliage. Juvenile leaves typically had lower specific leaf weights and were nutritionally superior to their adult counterparts. Specific leaf weights above 0.236 mg/mm² (associated with low water, i.e. = 56.5%, and nitrogen, i.e. = 1.23%, contents) were associated with reduced larval performance. Younger adult leaves, those with lower specific leaf weights, allowed slightly greater larval consumption.
• 4 When ovipositing, this eucalypt‐specific moth discriminates between leaf types of its heterophyllous hosts in favour of types with the lowest specific leaf weight. Less tough leaf types, which are also higher in nitrogen, enable neonates to attain larger body weights.

     

Density-related foraging behaviour in Closterocerus tricinctus, a parasitoid of the leaf-mining moth, Cameraria hamadryadella

• 1 We examined the foraging behaviour of the parasitoid wasp, Closterocerus tricinctus (Ashmead) (Chalcidoidea: Eulophidae), as it visited larvae of the leaf-mining moth, Cameraria hamadryadella (Lepidoptera: Gracillariidae), in an outbreak population.
• 2 We tracked females of C.tricinctus, recording the time spent searching for mines and handling host larvae. The density of leaf-mines (host larvae) and their condition were recorded for each leaf visited. A subset of leaves visited by C.tricinctus was enclosed in fine mesh bags so that foraging success could be determined by rearing or dissection. The average density of mines and the average leaf-area mined was estimated for a random sample of leaves from each tree.
• 3 The selection of leaves upon which to forage appears to be density-dependent. C.tricinctus visits leaves with leaf-mine densities twice the average, and when switching leaves lands directly on leaf-mines 5 times more often than expected assuming random landings.
• 4 The total time spent foraging on a leaf, the average time spent handling hosts, and the total search time within leaves tend to decline on leaves with many hosts, but the observed declines are not statistically significant.
• 5 The proportion of leaf-mines visited within a leaf is strongly inversely density-dependent. 30% of visits to leaf-mines are re-visits and 29% of handling time is spent re-handling previously visited hosts. Furthermore, only 21% of visits to mines lead to successful parasitism. We suggest that self-interference and the avoidance behaviour of the host may reduce the number of visits of leaf-mines by C.tricinctus within a leaf.
• 6 The effect of the strongly inversely density-dependent foraging investment within leaves is to offset the observed density-dependent pattern of leaf visitation making the overall spatial pattern of visitation by C.tricinctus to mines of C.hamadryadella inversely density-dependent.
• 7 We suggest that the uncertainty of C.tricinctus surviving on multiply mined leaves because of density-dependent host mortality due to intraspecific competition in high-density host populations, the rarity of high-density host populations, and the rarity of multiply-mined leaves in low-density host populations combine to select against an aggregative response within leaves by C.tricinctus.

     

Systematic within-tree variation in mountain birch leaf quality for a geometrid, Epirrita autumnata

Abstract.

• 1 We studied within-tree variation in leaf quality of the mountain birch, Betula pubescens ssp. tortuosa, for larvae of the autumnal moth, Epirrita autumnata.
• 2 The purpose of the study was to determine the possible occurrence of systematic differences in larval growth on short shoot leaves (i.e. leaves of the same age): among leaves facing in different compass directions, between leaves of lower and upper branches, among leaves on different positions within a branch and among leaves of different sizes within a short shoot. We also measured larval growth between short shoot and long shoot leaves (i.e. between leaves of different age).
• 3 The larvae grew best on leaves on the north side of trees and most poorly on south side leaves, the east and west sides being intermediate. Leaves from the upper branches supported larval growth better than leaves from the lower ones. The larvae grew better on the smallest leaf of each short shoot and were able to utilize it more efficiently than the two larger leaves. Short shoot leaves from the basal and middle parts of the upper branches of the trees were of better quality for the larvae than short shoot leaves from the tip part of the branches. The larval growth rate did not differ between short shoot and long shoot leaves. In general, within-tree variation in the larval growth rate was lower than variation among different trees.
• 4 Damage to leaves can decrease leaf quality for herbivores in the same year (rapidly inducible responses) or the following year(s) (delayed inducible responses). Our results show that systematic within-tree variation in larval growth can be as great as the effects of rapidly inducible responses and that variation among individual trees can be as great as the mean effects of delayed inducible responses.

     

Plant water deficits and insect responses: the preference of Corythucha arcuata (Heteroptera: Tingidae) for the foliage of white oak, Quercus alba

ABSTRACT.

• 1 The preference of Corythucha arcuata (Say) (Heteroptera: Tingidae) for the foliage of Quercus alba L. (Fagaceae) grown under water deficit was examined. Potted Q.alba saplings were grown under controlled levels of water deficit in a glasshouse. Adult C.arcuata were exposed to excised Q.alba foliage under controlled conditions in a growth chamber, and feeding preference assessed by recording the percentage of individuals feeding on leaves from each level of water deficit.
• 2 Two experiments were performed. In the first, all foliage was supplemented with water (via the petiole) to alleviate physical changes in the leaves that accompany plant water deficits. In the second experiment, leaves were not supplemented with water.
• 3 C.arcuata had no preference when presented water supplemented leaves, but preferred leaves that were fully hydrated when presented leaves that were not supplemented with water.
• 4 These results suggest that plant water deficits are important in determining the feeding preference of C.arcuata because they lead to avoidance of drought grown foliage. This avoidance may be caused by an increase in the metabolic cost to the herbivore of maintaining water balance when ingesting drought grown foliage or to an increase in foliage toughness.

     

Sun and shade leaves in Betula pubescens and Betula pendula

Summary

Measurements of the net photosynthesis and dark respiration rates of excised twigs from Betula pubescens Ehrh. subsp. odorata (Bechst.) Warburg and B. pendula Roth, at different light intensities were made using infra-red gas analysis. B. pubescens appears to possess leaves which on the basis of physiological responses can be described as sun and shade leaves. In the more open canopy of B. pendula differences between leaf types are less pronounced. The presence of sun and shade leaves is suggested as a means whereby the net assimilation rate of the shrubby growth form of B. pubescens can be increased. This type of mechanism becomes increasingly important at high altitudes and latitudes.     

Identifying inter‐ and intra‐guild feeding activity of an arthropod predator assemblage

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Multispecies interactions among a plant parasite,a pollinator and a seed predator affect the reproductive output of an invasive plant,Cytisus scoparius

Interactions between species pairs are almost always mediated by interactions with other species. The outcomes of these multispecies interactions are often difficult to predict and are rarely studied. In addition to their theoretical importance, multispecies interactions are also important for management situations. Where multiple agents are used to control invasive species, interactions between agents may either enhance or reduce the impacts on the target species, or may simply have additive effects. In this study, conducted in a Mediterranean‐type woodland in Australia, we examined how the interaction between an invasive legume, Cytisus scoparius (Leguminosae), its pollinator, Apis mellifera and a seed predator, Bruchidius villosus (Bruchidae), are modified by a native hemiparasitic vine, Cassytha pubescens (Loranthaceae). The parasite had a direct negative effect on C. scoparius, reducing flowering by 50% and consequently fruit and seed production. Despite having fewer flowers, infected plants had the same proportion of ‘tripped’ flowers, an indirect measure of pollinator visitation, as uninfected plants; although fruit formed on infected plants it was more likely to abort prematurely. Seed predation by B. villosus was lower on parasite‐infected C. scoparius plants than in uninfected plants. Although Ca. pubescens had an antagonistic effect on B. villosus, in consort, the two agents reduced overall seed production by an average of 62%. The acquired parasite Ca. pubescens was more effective in reducing reproductive output than the introduced seed predator, B. villosus, and shows potential as a biocontrol agent for C. scoparius. We documented a subadditive effect of two biological enemies on the invasive species, where the acquired parasite had a stronger effect than the introduced seed predator.     

Poleward increase in feeding efficiency of leafminer Stigmella lapponica (Lepidoptera: Nepticulidae) in a latitudinal gradient crossing a boreal forest zone

Damage to plant communities imposed by insect herbivores generally decreases from low to high latitudes. This decrease is routinely attributed to declines in herbivore abundance and/or diversity, whereas latitudinal changes in per capita food consumption remain virtually unknown. Here, we tested the hypothesis that the lifetime food consumption by a herbivore individual decreases from low to high latitudes due to a temperature-driven decrease in metabolic expenses. From 2016 to 2019, we explored latitudinal changes in multiple characteristics of linear (gallery) mines made by larvae of the pygmy moth, Stigmella lapponica, in leaves of downy birch, Betula pubescens. The mined leaves were larger than intact leaves at the southern end of our latitudinal gradient (at 60°N) but smaller than intact leaves at its northern end (at 69°N), suggesting that female oviposition preference changes with latitude. No latitudinal changes were observed in larval size, mine length or area, and in per capita food consumption, but the larval feeding efficiency (quantified as the ratio between larval size and mine size) increased with latitude. Consequently, S. lapponica larvae consumed less foliar biomass at higher latitudes than at lower latitudes to reach the same size. Based on space-for-time substitution, we suggest that climate warming will increase metabolic expenses of insect herbivores with uncertain consequences for plant–herbivore interactions.     

Within-tree and among-tree variation in growth of Epirrita autumnata on mountain birch leaves

Abstract.

• 1 We studied among-tree and within-tree variation in the growth of larvae of a geometrid, Epirrita autumnata, on mountain birch (Betula pubescens ssp. tortuosa) leaves at different hierarchical levels: among trees (genets), among ramets within trees, among branches within ramets, among shoots within branches and among leaves within shoots. We used only short shoot leaves, which burst simultaneously in spring.
• 2 Trees accounted for most of the variation in larval growth rate, but there was substantial variation also among ramets within trees, among branches within ramets, and among short shoots within branches. Variation among leaves within short shoots was negligible. When the probabilities from different experiments were combined, the differences were statistically significant at the tree, ramet and branch levels, and approached significance at the shoot level.
• 3 In different experiments, larval growth was from 9% to 54% lower on the worst tree than on the best tree of the experiment. On average, larval growth rate was in different experiments from 11% to 32% lower on the worst ramet than on the best ramet within tree, from 8% to 18% lower on the worst than on the best branch within ramet, and from 12% to 30% lower on the worst than on the best shoot within branch.
• 4 The amount of among-and within-tree variation shown by our results may have ecological and evolutionary implications: among-tree variation should select for discrimination by ovipositing females and dispersing larvae, within-tree variation should select also for optimal foraging behaviour of larvae.

     

Specialist pollinating seed predator exhibits oviposition strategy consistent with optimal oviposition theory

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Physicochemical tolerance,habitat use and predation are drivers of patterns of coexistence and exclusion among invasive and resident amphipods

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Preference induction and the benefits of floral resources for a facultative florivore

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Stomatal size,ploidy and polyembryony in Eriotheca Stellate Trichome Species Complex (Bombacoideae – Malvaceae) in the Cerrados of Brazil

• Geographic parthenogenesis, range expansion of apomictic plants after climate changes, has been described for Northern Hemisphere gametophytic apomicts. But similar trends have been observed for sporophytic apomicts of Cerrado, the savannas in Brazil. Eriotheca pubescens is a common Cerrado tree, an agamic complex of either hexaploid/polyembryonic apomicts or tetraploid/monoembryonic sexual individuals. Some populations have been described as a new species, Eriotheca estevesiae, all included in the Eriotheca Stellate Trichome Species Complex (ESTSC). Since breeding systems and ploidy are clearly associated with polyembryony and stomatal size, we used these ancillary features to map the reproductive and ploidy level traits of E. pubescens and E. estevesiae.
• Leaves and seeds were collected from individuals of 19 populations. Seeds were evaluated for the presence of polyembryony and leaves for stomatal measurements.
• Eight populations were monoembryonic while another eight were polyembryonic and for other three, the embryonic pattern was not readily verified. E. pubescens polyembryonic and hexaploid populations formed a homogeneous group, but monoembryonic plants were more variable. E. estevesiae populations were monoembryonic with smaller stomata. In contrast, some E. pubescens monoembryonic populations further south presented larger stomata. Despite these outliers, possibly mixed populations, stomatal size and embryonic pattern differed from northern to southern populations.
• Embryonic pattern and stomatal size indicated that northernmost populations of Eriotheca STSC (E. estevesiae) are diploid and sexual. Southernmost populations, mostly polyembryonic and with large stomata, are hexaploid and apomictic. This is in agreement with geographic parthenogenesis and range expansion of apomictic lineages to southern habitats available after the last glacial maximum.

     

Ellagitannins: defences of Betula nana against Epirrita autumnata folivory?

• 1 The induced resistance of the subarctic mountain birch Betula pubescens ssp. czerepanovii is a well‐characterized phenomenon, whereas the induced responses of Betula nana L., one of the parental species of mountain birch, have not yet been characterized. Betula nana is more resistant to several classes of insectivorous herbivores than the mountain birch, although the mechanisms responsible for the better ability to resist herbivores are not known.
• 2 The present study aimed to determine the metabolic changes that are induced by early season herbivory in B. nana leaves and to study the effects of rapidly induced resistance on the growth of Epirrita autumnata larvae.
• 3 Defoliation of B. nana was accomplished by E. autumnata larvae and leaf samples for chemical analyses were collected when the defoliating larvae were at their third and fifth instar. At the same time, laboratory assays for the growth and consumption rates of E. autumnata larvae were conducted.
• 4 The wounding of leaves by E. autumna larvae induced the production of ellagitannins (ETs) in B. nana. Intriguingly, the concentrations of protein‐bound amino acids were also induced by herbivory; however, an increase in proteins was not mirrored in the growth rate of larvae, which was less on the induced foliage. The decreased growth rate of larvae was apparently linked to the increased concentrations of oxidatively‐active ETs and the high concentration of ETs may explain the better resistance of this parental species compared with the hybrid mountain birch with its lower levels of ETs.