Health status and biological damage to tree leaves in green areas of Syktyvkar

The health status and biological damage to trees in green areas of Syktyvkar are studied. Birch and poplar are dominant trees among 103 species. The health status of trees is generally evaluated as good. The leaf damage by sucking and gnawing insects is increased, and the activity of leaf-mining and gall-forming insects is reduced. We identified 56 species of herbivorous arthropods, ten of which are new for the Komi Republic.     

Variation in rates of leaf abscission between plants may affect the distribution patterns of sessile insects

Summary At Sand Lake, Leon County, Florida, mines of Stilbosis quadricustatella, a leaf-mining moth, occur on sand live oak trees (Quercus geminata) over a broad range of densities. Some trees have fewer than 2% of their leaves mined (lightly infested), others up to 70% (heavily infested). Similar levels of infestation are maintained on the same trees year after year. There are no significant negative correlations of miner density per tree with any mortality factor that might explain miner preferences for certain trees. Nor is there a positive correlation with host leaf quality as measured by foliar nitrogen or by total or individual amino acid concentrations of host leaves. Egg-transfer experiments showed that larvae from eggs transferred to lightly infested trees were more likely to be killed by leaf abscission than were those that were transferred to and developed on heavily infested trees. This is the first demonstration that variation in rates of leaf abscission could be an important cause of the observed distribution pattern of sessile insects between conspecific host plants.     

Taxonomic isolation and the accumulation of herbivorous insects: a comparison of introduced and native trees

Abstract.

• 1 Evidence from leaf-mining insects on Fagaceous hosts suggests that range expansions of insects onto introduced trees often involve species that feed on native hosts closely related to the introduced host.
• 2 An examination of the herbivorous entomofauna of British trees illustrates that the size of the entomofauna is partially determined by the taxonomic isolation of the host tree.

     

Arboreal arthropod biodiversity in woodlands. II. The pattern of recovery of diversity on Melaleuca linariifolia following defaunation

This study examines the level of isolation of arthropod faunas present on specimens of the endemic woodland tree Melaleuca linariifolia by investigating the recovery of faunas after defaunation using insecticide. One tree from each of 21 pairs of trees was sprayed at the beginning of the project (early April 1994). After predetermined periods, three test trees were resprayed along with matched control trees. A total of 95 154 arthropods were collected and sorted during the project. The number of species present on the trees recovered within 16 weeks of spraying, with common species recolonizing within a fortnight. The rarer species both of mobile (Diptera) and relatively sedentary (Araneae) taxa reappeared at similar rates. Complete recovery of numbers occurred by week 8 after spraying. Evenness (as Simpson’s D) recovered over the first 2 months; however, both the number of individuals and the evenness continued to diverge from the pattern seen on the control trees until the end of the study. While the rate of movement of individuals and species was such as to provide an apparently complete set of replacement species within several months of perturbation, the structure of the community found on the trees was still seriously disrupted after 1 year. Comparison of the suites of species originally found on the trees with those found in the respray samples and the control samples showed that the set of colonizing species was no more similar to the original fauna of the tree than it was to those on the control tree. The relatively rapid colonization of the trees by a suite of rare species – not necessarily those that were on particular trees before perturbation – indicates that rarity was due neither to inability of the species to colonize the trees nor to the suitability of the trees for these species. Recovery of rare species was to a level similar to that found on the control trees. That the divergences from the controls continued (in number of individuals and in evenness), implies a definite connection between the different faunas of a tree and their partial isolation from fauna communities on other trees. Whatever the forces that maintain suites of species on each tree, it is not the ability of the species to reach and colonize trees, nor certain attributes of a tree, that make it suitable only for a particular subset of the species available. Trees are not isolated entities but neither are they part of a fully integrated community, either chronologically or spacially, and issues of scale are also likely to be important in understanding and estimating the dynamics and factors regulating biodiversity levels.     

Plant green-island phenotype induced by leaf-miners is mediated by bacterial symbionts

The life cycles of many organisms are constrained by the seasonality of resources. This is particularly true for leaf-mining herbivorous insects that use deciduous leaves to fuel growth and reproduction even beyond leaf fall. Our results suggest that an intimate association with bacterial endosymbionts might be their way of coping with nutritional constraints to ensure successful development in an otherwise senescent environment. We show that the phytophagous leaf-mining moth Phyllonorycter blancardella (Lepidoptera) relies on bacterial endosymbionts, most likely Wolbachia, to manipulate the physiology of its host plant resulting in the ‘green-island’ phenotype—photosynthetically active green patches in otherwise senescent leaves—and to increase its fitness. Curing leaf-miners of their symbiotic partner resulted in the absence of green-island formation on leaves, increased compensatory larval feeding and higher insect mortality. Our results suggest that bacteria impact green-island induction through manipulation of cytokinin levels. This is the first time, to our knowledge, that insect bacterial endosymbionts have been associated with plant physiology.     

Differences in insect species richness and faunal composition of birch seedlings, saplings and trees: the importance of plant architecture

Abstract. 1. Data are presented on the species richness and faunal composition of herbivorous insects on birch seedlings, saplings and trees at one site in Northern England.
2. Species richness of insect herbivores in equal-sized samples from birch seedlings and trees was similar through most of the season.
3. Effects of plant architecture were confined to the first sampling date, when seedling faunas were species poor compared with trees – possibly due to safe overwintering sites on the extensive bark, twigs and buds of trees.
4. The faunal composition of birch seedlings, saplings and trees was also similar. Out of a total of 112 recorded species of herbivores, only one aphid species was confined to seedlings.
5. Similarly, no evidence for clear-cut vertical stratification of insects within trees was found.
6. Species turnover as host plants mature ('horizontal' stratification) and vertical stratification within trees add little to the high overall species richness of birch-feeding insects in Britain, contrary to the predictions of Lawton (1983).     

Invasion,alien control and restoration: Legacy effects linked to folivorous insects and phylopathogenic fungi

Invasive alien trees increase native tree stress and may increase attack by herbivores and pathogenic fungi. Alien tree removal should ameliorate such impacts. Here we compared the levels of damage by phylopathogenic fungi and folivorous insects on Brabejum stellatifolium and Metrosideros angustifolia (native trees) and Acacia mearnsii (invasive tree species) among near‐pristine, invaded and restored sites. Generally, foliar damage levels were higher at invaded than at near‐pristine sites. Damage levels at restored sites were similar, or even higher than those at invaded sites. Decreased native tree species richness did not explain these patterns, as restored sites had native tree species richness levels similar to those of near‐pristine sites. Increased host abundance and leaf nitrogen content did not significantly correlate with increased damage in most cases. Therefore, plant species richness recovers following restoration, but native trees still experience increased pressure from folivores and phylopathogenic fungi, which may even exceed levels experienced at invaded sites, thus impacting recovery trajectories.     

Invertebrate predation of leaf-miners at low densities

Abstract.

• 1 Predation on a species of leaf-mining insect, Eriocraniella sp., by two species of ants, Crematogaster ashmeadii Mayr and Pseudomyrmex brunnea F. Smith, is documented.
• 2 Exclusion experiments show that ants and other terrestrial invertebrates can greatly contribute to mortality of leaf-miners and significantly decrease survivorship of the larval stages even when densities are low.
• 3 Comparison of two leaf-mining species, Eriocraniella sp. and Cameraria sp. nov. Davis, indicates that factors of mortality depend on the maturity of the leaf being mined.

     

Tree species preferences of foraging insectivorous birds in a northern hardwoods forest

Summary Birds searching for insects in the canopy of a northern hardwoods forest depart significantly from random in their use of tree species, even when these trees are generally similar in life form. All 10 foliage-dwelling bird species in the Hubbard Brook forest showed preferences for Yellow Birch, most had an aversion to Beech and Sugar Maple, and a few had special preferences for conifers or White Ash. Birds that glean prey from leaves had stronger tree species preferences than those that often hover for their prey, and were more influenced by tree species differences in foliage structure. The less common bird species and those for which northern hardwoods are marginal habitat had the most pronounced tree-species preferences. Food densities which are higher on Yellow Birch and specific adaptations to foraging in trees with particular foliage structures are considered major factors responsible for the observed tree species preferences. The implications of these findings for bird community structure and for forest management practices are discussed.     

Are tree trunks habitats or highways? A comparison of oribatid mite assemblages from hoop-pine bark and litter

Abstract Oribatid mites (Acari: Oribatida) are among the most diverse and abundant inhabitants of forest soil and litter, but also have species-rich assemblages on bark and in the canopies of trees. It is unclear whether the trunk of a tree acts simply as a 'highway' for movement of mites into and out of the canopy, or whether the trunk has a distinctive acarofauna. We compare oribatid assemblages from the trunk bark of hoop pine ( Araucaria cunninghamii ) with those from litter collected beneath the same trees. A 1.0 by 0.5 m area of bark was sampled from three trees at each of five sites using a knockdown insecticide. A 1-L sample of leaf litter was collected as close as possible to the base of each sampled tree. Mites were extracted using Tullgren funnels, identified to genus and morphospecies, and counted. Assemblages were almost 100% distinct, with only one oribatid morphospecies ( Pseudotocepheus sp.) collected from both litter and bark. Litter had a higher taxon richness than bark in total and per sample, but oribatids made up a greater percentage of the acarofauna in the bark samples. We had expected that the more consistent physical substrate of bark would be reflected in greater similarity of oribatid faunas on trunks than in litter; however, the opposite proved to be the case. We conclude that hoop-pine trunks are habitats rather than highways for oribatid mites. Based on the observed higher turnover among bark faunas, tree trunks may represent habitat islands whose colonisation by particular oribatid species is more stochastic than that of the more continuous 'sea' of litter.     

The assessment of arboreal insect fauna: comparisons of knockdown sampling and faunal lists

Abstract. 1. A comparison is made between the fauna of six British tree species sampled by pyrethrum knockdown and the faunal lists in the literature for the same tree species.
2. Conspecific trees vary both in abundance of arthropods and their proportional distribution across taxa, but there are important overriding differences between tree species.
3. The percentage similarity in faunal composition between tree species reflects the ecological specificity of the arthropod groups used for the comparison.
4. The similarity in species composition between tree species is least for phytophages, the guild most closely associated with particular tree species, The two species of Salix are most similar in their fauna for most guilds.
5. About 40% of the entirely phytophagous species in the faunal lists for native trees were found in the knockdown samples.
6. The proportion of individuals of predominantly phytophagous taxa collected that belong to the relevant faunal lists ranges from 0.39 to 0.99.
7. Those species found in the knockdown samples which are not included in faunal lists none the less contribute to the trophic web of the tree.
8. The relative species richness of arboreal faunas assessed from knockdown samples parallels that derived from faunal lists.
9. The two approaches to the categorization of arboreal faunas, knockdown sampling and faunal lists, provide comparable data.     

Eucalypt responses to fertilization and reduced herbivory

Summary We manipulated soil fertility and insect attack for two species of Eucalyptus in natural stands of subalpine woodland on shallow, infertile granitic soils. E. pauciflora and E. stellulata responded in similar ways to simultaneous insecticide and fertilizer treatments. Eliminating herbivorous insects produced the largest changes — improved plant growth, increased leaf N and P, and reduced leaf specific density. Fertilizer regime modified some leaf properties, but had little effect on tree growth. E. stellulata trees were initially shorter than E. pauciflora, but grew faster without herbivores; by the end of the experiment both species were the same size when herbivores were removed. Foliage N and P levels increased most in trees with the most balanced fertilizer addition (NPK), and increased in all trees protected from insects, regardless of fertilizer regime. In this system, herbivorous insects exacerbated the effects of nutrientpoor soils, and may affect dominance of Eucalyptus species in mature forests.     

The arboreal ants of a Neotropical rain forest show high species density and comprise one third of the ant fauna

In tropical rain forests, the ant community can be divided into ground and arboreal faunas. Here, we report a thorough sampling of the arboreal ant fauna of La Selva Biological Station, a Neotropical rain forest site. Forty-five canopy fogging samples were centered around large trees. Individual samples harbored an average of 35 ant species, with up to 55 species in a single sample. The fogging samples yielded 163 observed species total, out of a statistically estimated 199 species. We found no relationship between within-sample ant richness and focal tree species, nor were the ant faunas of nearby trees more similar to each other than the faunas of widely spaced trees. Species density was high, and beta diversity was low: A single column of vegetation typically harbors at least a fifth of the entire arboreal ant fauna. Considering the entire fauna, based on 23,326 species occurrence records using a wide variety of collecting methods, 182 of 539 observed species (196 of 605, estimated statistically) were entirely arboreal. The arboreal ant fauna is thus about a third of the total La Selva ant fauna, a robust result because inventory completeness was similar for ground and arboreal ants. The taxonomic history of discovery of the species that make up the La Selva fauna reveals no disproportionately large pool of undiscovered ant species in the canopy. The "last biotic frontier" for tropical ants has been the rotten wood, leaf litter, and soil of the forest floor.     

Salicaceae-Feeding Leaf-Mining Insects in Siberia: Distribution,Trophic Specialization,and Pest Status

This paper provides an overview of the leaf-mining insect community feeding on willows (Salix spp.) and poplars (Populus spp.) in Siberia. According to published data and our own observations, 50 leaf-mining insect species (i.e., 24 species of Lepidoptera, 15 Coleoptera, 6 Diptera, and 5 Hymenoptera) feed on those two plant genera in Siberia. Using an integrative approach combining field work, morphological and DNA barcoding analyses, we identified 32 leaf-mining insect species from 14 regions across Siberia (i.e. 64% of all leaf-mining species known on Salicaceae in this part of Russia). Among them, 26 species most often found in parks and botanical gardens, represented new faunistic records for several poorly explored regions of Siberia. We have more than doubled the list of Salicaceae-feeding leaf-mining insects in Tomsk oblast, Altai krai, and the Republic of Tuva, and for the first time provided data on leaf-miners for the Khanty–Mansi Autonomous Okrug. The micromoth Phyllocnistis gracilistylella (Gracillariidae), recently described from Japan, was found on a new host plant (Salix caprea) in the south of Krasnoyarsk krai, is new for Russia. Eight leafmining insect species (i.e., five gracillariids: Phyllocnistis labyrinthella, Ph. unipunctella, Phyllonorycter apparella, Ph. sagitella, and Ph. populifoliella; two beetles: Zeugophora scutellaris and Isochnus sequensi; and one sawfly: Heterarthrus ochropoda) can outbreak on poplars, most often in urban plantations, botanical gardens, and plant nurseries in Siberia, and can also affect natural stands. Forty-five species of 50 leaf-mining insects known to feed on willow and poplar in Siberia also occur in Central and Eastern Europe. The remaining five species (Phyllocnistis gracilistylella, Phyllonorycter sibirica, Heterarthrus fasciatus, Tachyerges dauricus, and Isochnus arcticus) are recorded in Asia only. Species richness of the family Gracillariidae, the most diverse on Salicaceae in Siberia, displays 80% similarity to that in the European part of Russia and 71% to the Russian Far East. We discuss the faunal similarity of these regions and highlight the importance of applying an integrative approach combining ecological, morphological analyses, and DNA barcoding to explore and characterize the insect fauna of poorly studied regions of Asian part of Russia.     

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.     

Evolutionary dynamics of host-plant use in a genus of leaf-mining moths

Abstract. We used nuclear 28S rDNA sequence data to estimate the phylogeny of 77 leaf-mining Phyllonorycter (Gracillariidae) moth species, including all 55 British species, feeding on 44 different plant genera. There was strong support for both the monophyly of Phyllonorycter and the placement of the genus Cameraria as its sister group. Host-plant use was mapped onto the moth phylogeny and investigated statistically in several ways. First, we show that the estimated level of cospeciation between leaf miners and their host plants is not greater than expected by chance, despite the physical intimacy of the association. Nevertheless, the pattern of host-plant use is far from random, with closely related Phyllonorycter species generally feeding on closely related plants. However, although Phyllonorycter species from a given host plant tend to form distinct clades, there is also statistical support for multiple independent colonizations of some host-plant taxa (e.g. the order Rosales and the genus Corylus ). Despite numerous host shifts, most Phyllonorycter species feed on trees and the few species that attack shrubs or herbs have mostly acquired these habits independently. There is also limited evidence that host shifts to herbs are more likely from shrubs than from trees. Similarly, most species mine the lower surface of leaves but the few upper-surface miners have each evolved the habit independently. Consequently, these shifts to new adaptive zones have not led to substantial radiations.     

Parasites of the Patagonian toothfish, Dissostichus eleginoides Smitt 1898, in different parts of the Subantarctic

The parasite faunas of the Patagonian toothfish Dissostichus eleginoides from six locations around the Southern Ocean were studied and compared. Thirty-two parasite taxa were found. Ten parasite species are reported from D. eleginoides for the first time and some other previously reported species were new locality records. Sample size at Shag Rocks was sufficient to examine the effect of intrinsic host factors, including sex and length, on the parasite fauna and these results are discussed here. Some parasite species were found only in certain areas. Sørensens similarity index indicated that the parasite faunas at Heard, Maquarie and Prince Edward Islands were the most similar, while those from the Ross Sea was the most dissimilar. There may be a gradual decrease in parasite diversity the further east the samples were collected around the Southern Ocean.     

The origin of autumn colours by coevolution

We lack an adaptive explanation for a striking phenomenon, that of bright colours displayed in autumn by the leaves of many deciduous trees. The usual explanation is that it is simply a non-adaptive secondary effect of leaf senescence. A game-theoretic model of biological signalling provides an adaptive hypothesis for autumn colours showing that they can be the result of a process of coevolution between insects and trees: if leaf colour acts as a warning indicator of the tree's vigour to autumn parasite insects, trees can gain advantage from the reduction of parasite load and insects can gain advantage from location of the most profitable hosts to lay their eggs. The results of the model are consistent with Zahavi's handicap principle. Possible explanations for the origin of the system and evidence from natural history are discussed.     

Causes of vertical stratification in the density of Cameraria hamadryadella

1. The density of Cameraria hamadryadella, a leaf-mining moth, is vertically stratified within the crown of oak trees. It occurs at higher densities on foliage in the lower crown. 2. Oviposition preference tests indicate that females display no preference to oviposit on foliage from the lower tree crown over foliage from the upper tree crown. 3. Experiments in which potted trees were placed at various heights indicate that foliage nearest ground level receives more oviposition, and that the higher rates of oviposition on foliage near the ground is not caused by differences in quality between foliage from low or high in the tree crown. 4. Host-plant- and natural-enemy-mediated juvenile mortality and the abundance of parasitoids did not differ between the upper and lower crown. 5. Vertical differences in the timing of leaf production within the tree crown are unlikely to account for the observed gradient in the abundance of C. hamadryadella. Furthermore, the mean date of leaf fall does not differ among heights within the tree crown. 6. It is argued that microclimatic gradients and interspecific competition are also unlikely to account for the observed gradients in the density of C. hamadryadella within the tree crown. 7. Because of the absence of effects of other potentially causal factors, the most likely explanation for the gradient in density of C. hamadryadella is a lack of movement by females into the upper tree crown from overwintering, emergence, or resting sites located in the lower tree crown, combined with egg depletion by females as they move from the lower to the upper tree crown. 8. It is suggested that the lack of movement and egg depletion hypothesis should serve as the null hypothesis in studies of vertical stratification of tree-feeding insects. In the absence of evidence of an effect of foliage quality, natural enemies, plant phenology, interspecific competition, or microclimate, the movement and egg depletion hypothesis is the most reasonable.