Multiple oviposition and larval feeding strategies in Euphydryas maturna (Linné, 1758) (Nymphalidae) at two disjoint European sites

Globally, Euphydryas maturna is a polyphagous butterfly species. At our study sites in Italy and Germany however, the plant used for egg-laying was almost exclusively Fraxinus excelsior. Nevertheless, in Germany, two egg-batches were found on Ligustrum vulgare and one on Viburnum opulus. Females lay their egg-batches at low heights and mostly on small trees (but not <1 m). At the end of the flight season, small egg-batches are laid and we conclude that these are late batches laid by “old females”. Egg-batches and pre-diapause larval webs are often clustered on certain trees and even leaves. This was shown to be a result of female behaviour and not of habitat quality, since the trees chosen were different in subsequent years. Individual females may return for laying further egg-batches to the place of the first egg-deposition and other females follow, since the survival of pre-diapause larvae is higher when more larval webs are on one tree. A further possible advantage during hibernation is discussed. In Italy, post-hibernation larvae form two distinct cohorts: larvae feeding on herbaceous plants (Plantago major, P. minor, Veronica hederifolia), and larvae feeding on Fraxinus excelsior. Although the latter group starts feeding later and pupates later, it reaches the same pupation weight. At our German site, post-hibernation larvae were found almost exclusively on F. excelsior. In fact, we observed larvae searching for food on F. excelsior while the buds of this tree were still closed. We also found larvae searching for food in the herbal layer without finding suitable plants. In some areas, larvae have to wait for the buds of the ash tree to open. Our data suggest that conservation strategies for E. maturna must be site specific according to food plant use of pre- and post-hibernation larvae and habitat type.     

Micromorphological differences between some European and American <Emphasis Type="Italic">Fraxinus</Emphasis> (<Emphasis Type="Italic">Oleaceae</Emphasis>) species

Micromorphological differences in leaves and pollen between two American (Fraxinus americana L., F. pennsylvanica Marshall) and two European (F. angustifolia Vahl, F. excelsior L.) ash species were studied using scanning electron microscope. The types, dimensions and distribution of characteristic trichomes were established and measured. Capitate hairs on the leaves had the same shape in all researched ash species. Acicular hairs were regularly present in two American ash species, but very rarely in the glabrous phase of F. angustifolia and F. excelsior. Only F. americana had coronulate abaxial surface of leaves. Pollen of F. angustifolia and F. excelsior had 3 (tricolpate) apertures, and F. americana and F. pennsylvanica 4 (stephanocolpate) apertures. Based on the appearance of the reticulum it’s possible to clearly distinguish all four species. F. angustifolia and F. pennsylvanica had muri with transversal ridges and seldom granules. Muri of F. excelsior and F. americana had slightly visible transversal ridges, and because of that noticeable granules.     

Investigations on the endogenous levels of abscisic acid in a range of parasitic phanerogams

The endogenous levels of abscisic acid in the parasitic phanerogamsArceuthobium oxycedri (DC) Bieb.,Cassytha filiformis L.,Lathraea squamaria L.,Melampyrum pratense L.,Orobanche hederae Duby., andViscum album L. were investigated. In general, the content of abscisic acid was high in parasites which deprive their hosts of both phloem- and xylem-transported substances and much lower in those that deprive their hosts of sap from the xylem only. Within the parasites studied in more depth (e.g.,Orobanche hederae, Lathraea squamaria, andMelampyrum pratense) the highest abscisic acid levels were found in their sink regions, especially in their inflorescences. It is suggested that a high concentration of abscisic acid is associated with plant tissues showing a high demand for phloem-transported substances. The possible role of abscisic acid in such tissues is discussed.     

Resistance to a fungal pathogen and host plant specialization in the pea aphid

Herbivores that show host race formation on different plant species have proven to be valuable model systems for studying the evolution of specialization and speciation. Here, we use the pea aphid, Acyrthosiphon pisum, to investigate a possible link between specialization on two host plant species, Lotus uliginosus and Trifolium pratense, and resistance to a natural enemy, the fungal pathogen Erynia neoaphidis. Pea aphids collected on either plant species in the field showed in most cases poor survival on the alternate host plant. Furthermore, pea aphids specialized on T. pratense were very resistant to E. neoaphidis, whereas aphids specialized on L. uliginosus were susceptible. This susceptibility was not influenced by the actual food plant on which the assays were conducted. We discuss how selection from natural enemies may influence the process of specialization and race formation, and how specialization can affect the evolution of resistance.     

Patch occupancy of two hemipterans sharing a common host plant

Aim Two hemipteran species were chosen as a study system for the comparative analysis of patch occupancy and spatial population structure of insects sharing a common host plant. This study tested whether (1) the incidence in the host plant patches differed between the two species, and (2) the two species exhibited a different spatial population structure, i.e. were they affected differentially by isolation and area of the host plant patches. Location The porphyry landscape north of Halle (Saale) in Germany comprising 506 patches of the host plant Brachypodium pinnatum. Methods The host plant patches were surveyed for the two hemipterans. To assess the influence of patch quality on species occurrence the patches were characterized by mean cover abundance of B. pinnatum, type of subsoil, slope, exposure, and shading. The spatial configuration of the patches was considered by patch area and isolation. The influence of the habitat factors and the spatial configuration on the occupancy of the two species was analysed by logistic regression. Results Adarrus multinotatus was found in 441 patches, while Neophilaenus albipennis was found in only 90 patches. While A. multinotatus showed virtually no relationship to the habitat factors, the occupancy of N. albipennis was influenced by subsoil type, cover abundance, and shading. The effects of area and isolation on occupancy of the patches also differed between the two species. The occupancy of N. albipennis was determined largely by area and isolation, whereas in A. multinotatus no considerable effect of spatial configuration was found. Main conclusions The study revealed a marked difference between the two hemipteran species in respect of spatial population structure. Adarrus multinotatus built up a ‘patchy population’, whereas N. albipennis showed a ‘metapopulation’ structure within the same set of patches in the same landscape. Spatial population structure was found to be not only a function of spatial configuration of habitat patches, but population structure differed between the habitat generalist A. multinotatus and the habitat specialist N. albipennis.     

Defining the twig fungal communities of Fraxinus species and Fraxinus excelsior genotypes with differences in susceptibility to ash dieback

Ash dieback disease (caused by Hymenoscyphus fraxineus) has affected European ash species (Fraxinus spp.) in recent decades. However, some Asian and American species of Fraxinus and certain genotypes of Fraxinus excelsior are less affected by the disease. We used ITS1-metabacoding to explore the drivers influencing diversity and composition of the twig fungal communities of Fraxinus species and F. excelsior genotypes. Our results revealed that fungi in the classes Eurotiomycetes and Dothideomycetes were among the most prevalent taxa in both Fraxinus species and F. excelsior genotypes. The diversity of the fungal communities differed significantly among Fraxinus species and could be explained by seed origin. Neither host genotype nor season had a significant effect on the community diversity of F. excelsior genotypes. On the other hand, the composition of twig fungal communities differed significantly among host species and among F. excelsior genotypes, and in F. excelsior there was also a significant effect of season on the composition of the fungal community. We did not find a clear effect of ash dieback susceptibility on either diversity or composition of fungal communities in twigs of Fraxinus species, although the effect was significant on the composition of fungal communities among F. excelsior genotypes. Our results demonstrated differences in fungal communities among species of Fraxinus and of F. excelsior genotypes, suggesting specific relationship between individual host genotypes and endophytic fungi.     

Host plant relationships of an endangered butterfly, Lopinga achine (Lepidoptera: Nymphalidae) in northern Europe

The aim of the present study was to evaluate—in a geographic perspective—the role of host plant as a determinant of habitat quality for Lopinga achine, a satyrine butterfly endangered over much of its European range. Laboratory trials were performed to record host choices made by the ovipositing females as well as by neonate larvae. In rearing experiments, growth performance and mortality on different host plants was determined. Oviposition was found to be indiscriminate but larvae were shown to be able to choose between host plants, with the choices made broadly consistent with growth performance of the larvae on particular hosts. Nevertheless, most grasses and sedges offered were found to support larval development reasonably well. No clear superiority of the previously suggested primary host plant Carex montana could be shown. Importantly, no differences in host plant relationships were found between the populations of Sweden, western Estonia and eastern Estonia. In particular, the larvae originating from eastern Estonian populations developed on C. montana equally well even if the plant is absent from their native habitat. In the context of species conservation, one should conclude that L. achine is polyphagous enough on various grasses and sedges so that the presence of any particular host species cannot be a critical component of habitat quality. Nevertheless, some preference to broad- and soft-leaved hosts, as well as sensitivity to host wilting, may partly explain the butterfly’s preference to moist forest habitats, further emphasizing the central role of habitat management in the conservation practice of this species. In turn, the absence of ecological differences between geographic populations should enable conservationists to successful transfer their experience across national boundaries.     

Infection with the fungal endophyte Epichloë festucae may alter the allelopathic potential of red fescue

Red fescue (Festuca rubra) is a perennial grass used as both forage and turfgrass. Asymptomatic plants of this species are systemically infected by the fungal endophyte Epichloë festucae, which has a beneficial effect on the infected plants. The aim of this study was to determine the effect of the endophyte Epichloë festucae on the allelopathic potential of F. rubra against four associated pasture species that are also considered as weeds in lawns, Trifolium pratense, Trifolium repens, Lotus corniculatus and Plantago lanceolata. Two experiments were designed to evaluate the allelopathic effect of extracts from the roots and leaves of endophyte‐infected (E+) and non‐infected (E?) plants on the germination and seedling growth of the four target species. Regardless of the endophyte status of the host plant, leaf extracts elicited a stronger reduction in germination and seedling growth than root extracts. Extracts from E+ plants reduced the speed of germination index of Trifolium spp. to a greater extent than those from E? plants. Radicle length of the target species was the parameter most affected by the presence of the endophyte in F. rubra. Root extracts from E+ plants had a greater inhibitory effect on the radicle growth of the target species than did root extracts from E? plants. A greater concentration in total phenolic compounds was found in the roots of E+ plants than of E?; however, this difference was not observed in the leaves. Thus, the allelopathic potential of F. rubra is altered in infected plants.     

Non‐target habitat exploitation by Trichogramma brassicae (Hym. Trichogrammatidae): what are the risks for endemic butterflies?

Abstract 1 Trichogramma brassicae Bezdenko is inundatively released against the European corn borer in Switzerland. Because parasitoids dispersing from the release fields might pose a threat to native butterflies, the searching efficiency of T. brassicae was investigated in nontarget habitats. 2 In field studies, T. brassicae was released at rates of 120 000 females/ha. Parasitism of sentinel Ephestia kuehniella egg clusters was 1.6–3.6% in meadows and 2.0–4.0% in flower strips. The respective figures were 57.6–66.7% and 19.2–46.9% in maize, significantly higher than the parasitism rates in the nontarget habitats. Experiments carried out in small field cages confirmed these results: Again, significantly higher parasitism rates were found in maize compared to meadows and flower strips, and also compared to hedgerows (in sleeve cages). 3 To elucidate potential factors underlying the low searching efficiency in nontarget habitats, the behaviour of individual T. brassicae females was investigated on four meadow plants comparatively to maize and a filter paper control. Mean (±SE) walking speed on maize was 2.2 ± 0.2 mm/s, similar to three of the plants tested and filter paper but significantly higher than on Trifolium pratense (0.85 mm/s). A higher turning rate was found on T. pratense, Viola wittrockiana and Plantago lanceolata, in contrast to the longer leaved maize and Alopecurus pratensis. The number of wasps leaving the plant within the observation period differed significantly between plant species, and was twice as high for T. pratense (and the filter paper control) compared to the other plant species. 4 In a choice experiment carried out in a climate cabinet with all five host plant species in cages, we obtained the highest parasitism rates on maize and the lowest parasitism on T. pratense, thus confirming the behavioural observations. 5 In conclusion, there is evidence for a decreased searching efficiency on plants in nontarget habitats compared to maize. However, the data explain only part of the differences found between parasitism in maize compared to nontarget habitats. Other factors, such as the structural complexity of a habitat, may also play a role. We conclude that the risk for butterfly populations in the tested nontarget habitat due to mass released T. brassicae is low.     

Ability to gall: the ultimate basis of host specificity in fig wasps?

1. Fig trees (Ficus spp.) and their host‐specific pollinator fig wasps (Agaonidae) are partners in an obligate mutualism. Receptive phase figs release specific volatiles to attract their pollinators, and this is generally effective in preventing pollinator species from entering figs of the wrong hosts. 2. If entry is attempted into atypical host figs, then ostiole size and shape and style length may also prevent reproduction. In spite of these barriers, there is increasing evidence that fig wasps enter atypical hosts, and that this can result in hybrid seed and fig wasp offspring. 3. This study examines the basis of pollinator specificity in two dioecious fig species from different geographical areas. Kradibia tentacularis pollinates Ficus montana in Asia. Ficus asperifolia from East Africa is closely related but is pollinated by a different species of Kradibia. 4. In glasshouses, K. tentacularis was attracted to its normal host, F1s and backcrosses, but only rarely entered figs of F. asperifolia. Foundresses were able to lay eggs in hybrids, backcrosses, and F. asperifolia, although flower occupancy was lowest in F. asperifolia figs and intermediate in hybrids. 5. The fig wasp failed to reproduce in female F. montana, male F. asperifolia, and male F1s, and most but not all backcrosses to F. montana. This was a result of the failure to initiate gall production. 6. Host specificity in this fig wasp is strongly influenced by host volatiles, but the ability to gall may be the ultimate determinant of whether it can reproduce.     

Lichen diversity and red-listed lichen species relationships with tree species and diameter in wooded meadows

This study provides a unique large dataset of total epiphytic lichen diversity (fruticose, foliose and crustose species) and composition on 1,294 trees of 17 tree species in wooded meadows in Sweden and Estonia, the Baltic region. The inventory (25,380 observations and 246 lichen taxa) clearly illustrated that Ulmus minor, Quercus robur and Fraxinus excelsior contributed most significantly to epiphytic lichen richness and number of red-listed species. In Sweden, average single tree α richness was 22.2 on Ulmus (only in Sweden), 21.6 on Quercus (25.0 in Estonia) and 19.8 on Fraxinus (16.7 in Estonia), respectively. Ulmus hosted on average one red-listed species per tree, compared with 0.7 on Fraxinus (0.6 in Estonia), 0.4 on Quercus (0.7 in Estonia) and only 0.05 on Betula (same in Estonia). Lichen species composition and the average number of red-listed lichens were influenced by tree diameter on Fraxinus and Quercus, whilst no such pattern was evident on Ulmus. Randomized species accumulation curves of the dominating tree species illustrated that Fraxinus, Quercus and Ulmus supported α dominated lichen communities where individual trees hosted a substantial part of the total richness. Betula, on the other hand, supported β dominated communities where individual trees tended to be dissimilar and, therefore, more of the total richness existed as species turnover among host trees. Lichen species composition was influenced by tree species, and most notably, lichen species on Ulmus had a strong consistent clumping in ordination graphs, with many rare and red-listed lichens. The broadleaved deciduous trees within the wooded meadows clearly contribute greatly to the biodiversity of the Baltic region.     

Host-plant specialization by a non-herbivorous amphipod: advantages for the amphipod and costs for the seaweed

Studies of factors affecting host plant specialization by herbivores commonly highlight the value of the plant as both food and habitat, but often cannot distinguish the relative importance of these plant traits. A different approach is to study non-herbivorous animals that specialize on particular plants but do not feed on tissue from these plants. Such animals will not be affected directly by the nutritional, chemical, or morphological traits that determine the value of the plant as a food. This study reports on a filter-feeding amphipod, Ericthoniusbrasiliensis, that lives in domiciles it constructs by curling terminal segments of the green, calcified, and chemically defended seaweed Halimedatuna. We examined the temporal (1850s–1990s) and spatial (Caribbean, Mediterranean, and Pacific regions) scale of the association, the factors that may select for specialization on H. tuna, and the effect of the amphipod on growth of its host. Sampling along 125 km of coral reefs in the Florida Keys (USA) indicated that almost all populations of H. tuna had been colonized by this amphipod. Infested plants occurred on nine of ten reefs that supported H. tuna populations, with between 8 and 75% of the plants on those reefs colonized by the amphipod. For infested plants, 2–23% of all segments on each plant had been curled by the amphipod. Common co-occurring congeners of H. tuna (H. opuntia and H. goreaui) were never used for domicile construction. A survey of 1498 Halimeda specimens collected during the last 140 years and archived in the U.S. National Museum of Natural History (Smithsonian Institution, Washington, D.C.) indicated that the association has existed for >100 years and occurs throughout the Caribbean region, never in the Indo-Pacific or Mediterranean, and only on H. tuna. Predation by fishes could select for amphipod specialization on H. tuna. Laboratory experiments demonstrated that amphipods inhabiting curled segments of H. tuna were relatively immune from fish predation while those on the exterior surface of the plant or in open water were rapidly eaten. Segments of H. tuna are large enough to provide full protection from predators, while those of the co-occurring congeners H. goreaui and H. opuntia are of a size that may provide only partial protection. Experimental addition of E. brasiliensis to H. tuna plants in the field significantly decreased segment accumulation on infested relative to uninfested control plants. Whether this negative effect was a direct or indirect consequence of amphipod occupancy is unclear. Rolling plant portions into domiciles could directly decrease host growth by increasing shading and decreasing exposure of plant surface area to water column nutrient flux. Amphipod occupancy could indirectly slow net host growth if fishes selectively feed on plant sections occupied by amphipods. Underwater video showed that herbivorous fishes did not graze infested plants more than uninfested plants, but small predatory fishes did prefer feeding from infested plants. These non-herbivorous fishes may slow host growth by damaging the terminal meristematic tissues of plants during attacks on amphipods. This study demonstrates that habitat specialists can negatively impact hosts without consuming them and that specialization on a plant can occur due to its habitat value alone (as opposed to its value as a food). Received: 24 March 1998 / Accepted: 1 November 1998     

Estimating Coextinction Risks from Epidemic Tree Death: Affiliate Lichen Communities among Diseased Host Tree Populations of Fraxinus excelsior

At least 10% of the world’s tree species are threatened with extinction and pathogens are increasingly implicated in tree threats. Coextinction and threats to affiliates as a consequence of the loss or decline of their host trees is a poorly understood phenomenon. Ash dieback is an emerging infectious disease causing severe dieback of common ash Fraxinus excelsior throughout Europe. We utilized available empirical data on affiliate epiphytic lichen diversity (174 species and 17,800 observations) among 20 ash dieback infected host tree populations of F. excelsior on the island Gotland in the Baltic Sea, Sweden. From this, we used structured scenario projections scaled with empirical data of ash dieback disease to generate probabilistic models for estimating local and regional lichen coextinction risks. Average coextinction probabilities (Ā) were 0.38 (95% CI ±0.09) for lichens occurring on F. excelsior and 0.14 (95% CI ±0.03) when considering lichen persistence on all tree species. Ā was strongly linked to local disease incidence levels and generally increasing with lichen host specificity to F. excelsior and decreasing population size. Coextinctions reduced affiliate community viability, with significant local reductions in species richness and shifts in lichen species composition. Affiliates were projected to become locally extirpated before their hosts, illuminating the need to also consider host tree declines. Traditionally managed open wooded meadows had the highest incidence of ash dieback disease and significantly higher proportions of affiliate species projected to go extinct, compared with unmanaged closed forests and semi-open grazed sites. Most cothreatened species were not previously red-listed, which suggest that tree epidemics cause many unforeseen threats to species. Our analysis shows that epidemic tree deaths represent an insidious, mostly overlooked, threat to sessile affiliate communities in forested environments. Current conservation and management strategies must account for secondary extinctions associated with epidemic tree death.     

Hemiparasite abundance in an alpine treeline ecotone increases in response to atmospheric CO2 enrichment

Populations of the annual hemiparasites Melampyrum pratense L. and Melampyrum sylvaticum L. were studied at the treeline in the Swiss Alps after 3 years of in situ CO₂ enrichment. The total density of Melampyrum doubled to an average of 44 individuals per square meter at elevated CO₂ compared to ambient CO₂. In response to elevated CO₂, the height of the more abundant and more evenly distributed M. pratense increased by 20%, the number of seeds per fruit by 21%, and the total seed dry mass per fruit by 27%, but the individual seed size did not change. These results suggest that rising atmospheric CO₂ may stimulate the reproductive output and increase the abundance of Melampyrum in the alpine treeline ecotone. Because hemiparasites can have important effects on community dynamics and ecosystem processes, notably the N cycle, changing Melampyrum abundance may potentially influence the functioning of alpine ecosystems in a future CO₂-rich atmosphere.     

Cloning and analysis of a 6.8-kb rDNA intergenic spacer region of the European ash (Fraxinus excelsior L.)

The 6.8-kb rDNA intergenic spacer region of F. excelsior was isolated from a CsCl/actinomycin-D gradient and cloned into pUC18 for further characterization. We observed the presence of subrepeats delimited by HaeIII enzyme sites. These subrepeats were sub-cloned and 11 clones were sequenced. These corresponded to subrepeated elements of either 32 bp or 41 bp that shared a 23-bp common sequence in the 5 end. Within each family of subrepeats, the percentage of common nucleotides was 84.4% for the 5 32-bp subrepeats and 67.4% for the 640-bp subrepeats. Non-repeated HaeIII fragments of 450 bp and 650 bp were also sub-cloned. To compare homology at the IGS region between the rDNA spacers of F. excelsior and the three related species (F. oxyphylla, F. americana, F. ornus), we conducted Southern hybridization analyses using each member of the 32-bp and 40-bp subrepeat families and the unique 450-bp and 650-bp fragments as probes. These analyses indicated that (1) the American ash is more genetically distant from the other three species that the latter are from each other and (2) F. oxyphylla and F. excelsior are more closely related to each other than to F. ornus.     

Patch occupancy in the endangered butterfly Lycaena helle in a fragmented landscape: effects of habitat quality, patch size and isolation

While there is agreement that both habitat quality and habitat network characteristics (such as patch size and isolation) contribute to the occupancy of patches by any given species, the relative importance of these factors is under debate. This issue is of fundamental ecological importance, and moreover of special concern for conservation biologists aiming at preserving endangered species. Against this background we investigated patch occupancy in the violet copper Lycaena helle, one of the rarest butterfly species in Central Europe, in the Westerwald area (Rhineland-Palatinate, Western Germany). Occupied (n = 102) differed from vacant (n = 128) patches in altitude, size, connectivity, availability of wind shelter, in the abundance of the larval host-plant, in the abundance of a grass species indicating favorable habitat conditions and in the abundance of nitrophilous plants. Overall, patch occupancy was primarily determined by patch size, connectivity and the abundance of the larval host plant, while all other parameters of habitat quality were of subordinate importance. Therefore, our findings suggest that even for extremely sedentary species such as L. helle habitat networks are decisive and—next to the preservation of habitat quality—need to be an integral part of any conservation management for this species.     

A hemiparasite in the forest understorey: photosynthetic performance and carbon balance of Melampyrum pratense

• Melampyrum pratense is an annual root‐hemiparasitic plant growing mostly in forest understorey, an environment with unstable light conditions. While photosynthetic responses of autotrophic plants to variable light conditions are in general well understood, light responses of root hemiparasites have not been investigated.
• We carried out gas exchange measurements (light response and photosynthetic induction curves) to assess the photosynthetic performance of M. pratense in spring and summer. These data and recorded light dynamics data were subsequently used to model carbon balance of the hemiparasite throughout the entire growth season.
• Summer leaves had significantly lower rates of saturated photosynthesis and dark respiration than spring leaves, a pattern expected to reflect the difference between sun‐ and shade‐adapted leaves. However, even the summer leaves of the hemiparasite exhibited a higher rate of light‐saturated photosynthesis than reported in non‐parasitic understorey herbs. This is likely related to its annual life history, rare among other understorey herbs. The carbon balance model considering photosynthetic induction still indicated insufficient autotrophic carbon gain for seed production in the summer months due to limited light availability and substantial carbon loss through dark respiration.
• The results point to potentially high importance of heterotrophic carbon acquisition in M. pratense, which could be of at least comparable importance as in other mixotrophic plants growing in forests – mistletoes and partial mycoheterotrophs. It is remarkable that despite apparent evolutionary pressure towards improved carbon acquisition from the host, M. pratense retains efficient photosynthesis and high transpiration rate, the ecophysiological traits typical of related root hemiparasites in the Orobanchaceae.

     

Virulence of Hymenoscyphus albidus and H. fraxineus on Fraxinus excelsior and F. pennsylvanica

European ash (Fraxinus excelsior) is currently battling an onslaught of ash dieback, a disease emerging in the greater part of its native area, brought about by the introduction of the ascomycete Hymenoscyphus fraxineus (= Hymenoscyphus pseudoalbidus). The closely-related fungus Hymenoscyphus albidus, which is indigenous to Europe, is non-pathogenic when in contact with F. excelsior, but could pose a potential risk to exotic Fraxinus species. The North American green ash (Fraxinus pennsylvanica) is planted widely throughout Europe and regenerates naturally within this environment but little is known about the susceptibility of this species to ash dieback. We performed wound inoculations with both fungi (nine strains of H. fraxineus and three strains of H. albidus) on rachises and stems of F. excelsior and F. pennsylvanica under field conditions in Southern Poland. Necrosis formation was evaluated after two months on the rachises and after 12 months on the stems. After inoculation of H. albidus, only small lesions (of up to 1.3 cm in length) developed on the F. excelsior and F. pennsylvanica rachises, but with no significant distinction from the controls. Hymenoscyphus albidus did not cause necrotic lesions on the stems of either Fraxinus species. In contrast, H. fraxineus induced necroses on all inoculated rachises of both ash species with mean lengths of 8.4 cm (F. excelsior) and 1.9 cm (F. pennsylvanica). Necroses also developed on all of the inoculated F. excelsior stems (mean length 18.0 cm), whereas on F. pennsylvanica such lesions only occurred on about 5% of the stems (mean length 1.9 cm). The differences between strains were negligible. No necroses were observed on the control plants. Reisolations of H. albidus were only successful in around 8–11% of the cases, while H. fraxineus was reisolated from 50–70% of the inoculated organs showing necrotic lesions. None of the Hymenoscyphus species were isolated from the control plants. Our data confirm H. fraxineus’ high virulence with regards to F. excelsior and demonstrate a low virulence in relation to F. pennsylvanica under field conditions in Poland. Hymenoscyphus albidus did not express any perceivable pathogenicity on both host species.     

Habitat quality matters for the distribution of an endangered leaf beetle and its egg parasitoid in a fragmented landscape

Fragmentation, deterioration, and loss of habitat patches threaten the survival of many insect species. Depending on their trophic level, species may be differently affected by these factors. However, studies investigating more than one trophic level on a landscape scale are still rare. In the present study we analyzed the effects of habitat size, isolation, and quality for the occurrence and population density of the endangered leaf beetle Cassida canaliculata Laich. (Coleoptera: Chrysomelidae) and its egg parasitoid, the hymenopteran wasp Foersterella reptans Nees (Hymenoptera: Tetracampidae). C. canaliculata is strictly monophagous on meadow sage (Salvia pratensis), while F. reptans can also parasitize other hosts. Both size and isolation of habitat patches strongly determined the occurrence of the beetle. However, population density increased to a much greater extent with increasing host plant density ( = habitat quality) than with habitat size. The occurrence probability of the egg parasitoid increased with increasing population density of C. canaliculata. In conclusion, although maintaining large, well-connected patches with high host plant density is surely the major conservation goal for the specialized herbivore C. canaliculata, also small patches with high host plant densities can support viable populations and should thus be conserved. The less specialized parasitoid F. reptans is more likely to be found on patches with high beetle density, while patch size and isolation seem to be less important.     

Molecular biodiversity and population structure in common ash (Fraxinus excelsior L.) in Britain: implications for conservation

Current forestry policy promotes the use of local seed for new plantings, on the assumption that local material may be better adapted to local conditions. However, landscape‐scale genetic studies which are necessary to underpin conservation and breeding strategies are often lacking. We investigated molecular diversity in common ash (Fraxinus excelsior L.) sampled from 42 British and six French sites with microsatellites. Chloroplast haplotype H04 was the most common and widespread in Britain, although rare and localized individuals with H02 and H09 were also detected. In addition, three new chloroplast haplotypes were identified, and these were rare and highly localized. In terms of nuclear microsatellite markers, allelic richness differed between sites and decreased in an east to west direction. Differentiation between sites was often very low (mean F_ST 0.025), indicating few differences between the majority of sites. There was a clear excess of homozygotes (mean H_O 0.669, mean H_E 0.818) and a relatively high F_IS (mean 0.182), suggests a consistent level of inbreeding or a widespread Wahlund effect in many F. excelsior sites. Gene pool ancestry analysis suggested that the majority of British F. excelsior belongs to a single meta‐population which covers mainland western and central Europe. Three northern and western sites diverged markedly from the dominant population, and may represent remnants of two late potential Ice Age refugia in northern Britain. The data provide new information which will aid development of appropriate conservation policies for ash and other wind pollinated tree species.