Morphological ontogeny and complementary description of Neoseiulus subsolidus (Beglyarov) (Acari: Mesostigmata: Phytoseiidae).

The morphological ontogeny of Neoseiulus subsolidus (Beglyarov) (Acari: Mesostigmata: Phytoseiidae) was studied based on the specimens collected from Salix sp. (Salicaceae) leaves in Tyumen region and Altai Republic, Russia. All active life stages including larva, protonymph, deutonymph, adult female and male were described and illustrated. The taxonomic challenges in recognizing species in the canadensis species group are discussed.

3,7-Dimethylpentadecane: a Novel Sex Pheromone Component from Leucoptera sinuella (Lepidoptera: Lyonetiidae).

Leucoptera sinuella is a leaf-miner moth present in several regions in the world, which has been recently introduced into Chile. The larvae feed exclusively on the leaves of poplar and willow trees, and the damage caused by the feeding behavior poses a threat to the wood-producing industry. Besides, L. sinuella larvae invade nearby orchards for pupation, causing rejections in Chilean fresh fruit for export. Here we report the identification of the female-produced sex pheromone of L. sinuella as a first step towards the development of pheromone-based methods for pest management of this species. First, we analyzed hexane extracts of the abdominal glands of virgin females by gas chromatography coupled with mass spectrometry and identified the major compound in these extracts to be 3,7-dimethylpentadecane, while minor compounds in the extracts proved to be 3,7-dimethyltetradecane and 7-methylpentadecane. Structure assignments were carried out by comparison of retention times and mass spectra of the natural products with those of authentic reference samples. Second, we conducted field tests, which showed that traps baited with synthetic 3,7-dimethylpentadecane were significantly attractive to males in a dose-dependent response. Our results also showed that a mixture of 3,7-dimethylpentadecane, 3,7-dimethyltetradecane, and 7-methylpentadecane in proportions similar to those found in gland extracts was the most attractive lure.

Transcriptome analysis of contrasting resistance to herbivory by Empoasca fabae in two shrub willow species and their hybrid progeny.

Short rotation woody biomass cultivars developed from fast-growing shrub species of willow (Salix spp.) have superior properties as perennial energy crops for the Northeast and Midwest US. However, the insect pest potato leafhopper (PLH) Empoasca fabae (Harris) can cause serious damage and reduce yield of susceptible genotypes. Currently, the willow cultivars in use display varying levels of susceptibility under PLH infestation. However, genes and markers for resistance to PLH are not yet available for marker-assisted selection in breeding. In this study, transcriptome differences between a resistant genotype 94006 (S. purpurea) and a susceptible cultivar 'Jorr' (S. viminalis), and their hybrid progeny were determined. Over 600 million RNA-Seq reads were generated and mapped to the Salix purpurea reference transcriptome. Gene expression analyses revealed the unique defense mechanism in resistant genotype 94006 that involves PLH-induced secondary cell wall modification. In the susceptible genotypes, genes involved in programed cell death were highly expressed, explaining the necrosis symptoms after PLH feeding. Overall, the discovery of resistance genes and defense mechanisms provides new resources for shrub willow breeding and research in the future.

The use of Leaf Surface Contact Cues During Oviposition Explains Field Preferences in the Willow Sawfly Nematus Oligospilus.

After an insect herbivore has reached its host plant, contact cues from the leaf surface often determine host acceptance. We studied contact cues during oviposition behavior of a willow pest, the sawfly Nematus oligospilus (Hymenoptera: Tenthredinidae), a specialist feeder on Salix (Salicaceae) trees, and how it determines oviposition preference in lab and field conditions. We described the sequence of behaviors that lead to egg laying on the most and least preferred willow species. Then we studied the morphology of chemosensory structures present on the female antenna, cerci and ovipositor. Since phenolic glycosides (PGs) are the main secondary metabolites present in Salicaceae species, we investigated their role in host acceptance. We quantified these compounds in different willow species and correlated PG content with oviposition preference under lab and natural field conditions. We demonstrated a major role for contact cues in triggering N. oligospilus egg laying on the leaf surface of preferred willow genotypes. Firstly cues are sensed by antennae, determining to leave or stay on the leaf. After that, sensing is performed by abdominal cerci, which finally triggers egg laying. The lack of PGs in non-preferred species and the significant correlation observed between PGs, natural damage and oviposition preference suggest a role for these compounds in host selection. Our study suggests that in specialist feeders, secondary compounds normally acting as defenses can actually act as a susceptibility factor by triggering specific insect behavior for oviposition. These defensive compounds could be selected against to increase resistance.

A new species of Danothrips from Southwestern China (Thysanoptera: Thripidae).

Danothrips salicis sp. n. is described from young leaves of Salix sp. in Southwestern China. This species is similar to D. moundi, D. theifolii and D. trifasciatus, but can be distinguished by the colour of the fore wing, the median longitudinal split on tergite X of females, and in males by the situation of the median short thorn-like setae on tergite IX.

Genetic specificity of a plant-insect food web: Implications for linking genetic variation to network complexity.

Theory predicts that intraspecific genetic variation can increase the complexity of an ecological network. To date, however, we are lacking empirical knowledge of the extent to which genetic variation determines the assembly of ecological networks, as well as how the gain or loss of genetic variation will affect network structure. To address this knowledge gap, we used a common garden experiment to quantify the extent to which heritable trait variation in a host plant determines the assembly of its associated insect food web (network of trophic interactions). We then used a resampling procedure to simulate the additive effects of genetic variation on overall food-web complexity. We found that trait variation among host-plant genotypes was associated with resistance to insect herbivores, which indirectly affected interactions between herbivores and their insect parasitoids. Direct and indirect genetic effects resulted in distinct compositions of trophic interactions associated with each host-plant genotype. Moreover, our simulations suggest that food-web complexity would increase by 20% over the range of genetic variation in the experimental population of host plants. Taken together, our results indicate that intraspecific genetic variation can play a key role in structuring ecological networks, which may in turn affect network persistence.

Population Dynamics of an Insect Herbivore over 32 Years are Driven by Precipitation and Host-Plant Effects: Testing Model Predictions.

The interaction between the arroyo willow, Salix lasiolepis Bentham, and its specialist herbivore, the arroyo willow stem-galling sawfly, Euura lasiolepis Smith (Hymenoptera: Tenthredinidae), was studied for 32 yr in Flagstaff, AZ, emphasizing a mechanistic understanding of insect population dynamics. Long-term weather records were evaluated to provide a climatic context for this study. Previously, predictive models of sawfly dynamics were developed from estimates of sawfly gall density made between 1981 and 2002; one model each for drier and wetter sites. Predictor variables in these models included winter precipitation and the Palmer Drought Severity Index, which impact the willow growth, with strong bottom-up effects on sawflies. We now evaluate original model predictions of sawfly population dynamics using new data (from 2003-2012). Additionally, willow resources were evaluated in 1986 and in 2012, using as criteria clone area, shoot density, and shoot length. The dry site model accounted for 40% of gall population density variation between 2003 and 2012 (69% over the 32 yr), providing strong support for the bottom-up, mechanistic hypothesis that water supply to willow hosts impacts sawfly populations. The current drying trend stressed willow clones: in drier sites, willow resources declined and gall density decreased by 98%. The wet site model accounted for 23% of variation in gall population density between 2003 and 2012 (48% over 30 yr), consistent with less water limitation. Nonetheless, gall populations were reduced by 72%.

Taxonomic study of Central Asian species of the genus Macropsis Lewis, 1836 (Homoptera: Auchenorrhyncha: Cicadellidae: Macropsinae). II: redescriptions of poorly known species, new synonyms, and description of a new willow-dwelling species.

Macropsis validiuscula Dubovsky, 1966, M. vicina (Horvath, 1897) = M. populicola Dubovsky, 1966 = M. albinata Dubovsky, 1966, syn. n. = M. albidula Dubovsky, 1966, syn. n., M. iliensis Mityaev, 1971 and M. elaeagnicola Dubovsky, 1966 are redescribed and illustrated based on material from Tien Shan Mts. (Kyrgyzstan) and Ferghana Valley (Uzbekistan), M. tienschanica Tishetshkin sp. n. from West Tien Shan Mts. (Kyrgyzstan) is described. M. iliensis Mityaev, 1971 is recorded from Kyrgyzstan for the first time. Data on host plants and male vibrational calling signals for all species considered are provided.

Taxonomic study of Central Asian species of the genus Macropsis Lewis, 1836 (Homoptera: Auchenorrhyncha: Cicadellidae: Macropsinae). I: Redescriptions of willow-dwelling species from West Tien Shan Mountains.

Macropsis abdullaevi Dubovskiy, 1966 = M. arslanbobica Dlabola, 1967 syn. nov., M. ibragimovi Dubovskiy, 1966 and M. asiatica Dubovskiy, 1966 from West Tien Shan Mts. (Kyrgyzstan) are redescribed and illustrated based on material from type localities or/and adjacent territories. M. tarbagataica Mityaev, 1971 from Kazakhstan is recorded from West Tien Shan for the first time. Data on host plants and male vibrational calling signals for all species considered are provided.

An apparent trade-off between direct and signal-based induced indirect defence against herbivores in willow trees.

Signal-based induced indirect defence refers to herbivore-induced production of plant volatiles that attract carnivorous natural enemies of herbivores. Relationships between direct and indirect defence strategies were studied using tritrophic systems consisting of six sympatric willow species, willow leaf beetles (Plagiodera versicolora), and their natural predators, ladybeetles (Aiolocaria hexaspilota). Relative preferences of ladybeetles for prey-infested willow plant volatiles, indicating levels of signal-based induced indirect defence, were positively correlated with the vulnerability of willow species to leaf beetles, assigned as relative levels of direct defence. This correlation suggested a possible trade-off among the species, in terms of resource limitation between direct defence and signal-based induced indirect defence. However, analyses of volatiles from infested and uninfested plants showed that the specificity of infested volatile blends (an important factor determining the costs of signal-based induced indirect defence) did not affect the attractiveness of infested plant volatiles. Thus, the suggested trade-off in resource limitation was unlikely. Rather, principal coordinates analysis showed that this 'apparent trade-off' between direct and signal-based induced indirect defence was partially explained by differential preferences of ladybeetles to infested plant volatiles of the six willow species. We also showed that relative preferences of ladybeetles for prey-infested willow plant volatiles were positively correlated with oviposition preferences of leaf beetles and with the distributions of leaf beetles in the field. These correlations suggest that ladybeetles use the specificity of infested willow plant volatiles to find suitable prey patches.

Phytohormones and willow gall induction by a gall-inducing sawfly.

A variety of insect species induce galls on host plants. Several studies have implicated phytohormones in insect-induced gall formation. However, it has not been determined whether insects can synthesize phytohormones. It has also never been established that phytohormones function in gall tissues. Liquid chromatography and tandem mass spectrometry (LC/MS/MS) were used to analyse concentrations of endogenous cytokinins and the active auxin IAA in the gall-inducing sawfly (Pontania sp.) and its host plant, Salix japonica. Feeding experiments demonstrated the ability of sawfly larvae to synthesize IAA from tryptophan. Gene expression analysis was used to characterize hormonal signalling in galls. Sawfly larvae contain high concentrations of IAA and t-zeatin, and produce IAA from tryptophan. The glands of adult sawflies, the contents of which are injected into leaves upon oviposition and are involved in the initial stages of gall formation, contain an extraordinarily high concentration of t-zeatin riboside. Transcript levels of some auxin- and cytokinin-responsive genes are significantly higher in gall tissue than in leaves. The abnormally high concentration of t-zeatin riboside in the glands strongly suggests that the sawfly can synthesize cytokinins as well as IAA. Gene expression profiles indicate high levels of auxin and cytokinin activities in growing galls.

Conflicting mitochondrial and nuclear phylogeographic signals and evolution of host-plant shifts in the boreo-montane leaf beetle Chrysomela lapponica.

We conducted a phylogeographic study on the cold-adapted leaf beetle Chrysomela lapponica, that feeds on willow or birch, by sampling several populations throughout most of the geographic distribution of the species, and by sequencing for each individual one mitochondrial and two nuclear DNA fragments. Patterns of DNA sequence variation from the mitochondrial and nuclear loci, as displayed in the median-joining networks, appear to display contradicting historical signal: a deep genealogical divergence is observed with the mitochondrial genome between the Alpine population and all other populations found in the Euro-Siberian distribution of the species, that is completely absent with both nuclear loci. We use coalescence simulations of DNA sequence evolution to test the hypothesis that this apparent conflict is compatible with a neutral model of sequence evolution (i.e., to check whether the stochastic nature of the coalescence process can explain these patterns). Because the simulations show that this is highly unlikely, we consider two alternative hypotheses: (1) introgression of the mitochondrial genome of another species and (2) the effect of natural selection. Although introgression is the most plausible explanation, we fail to identify the source species of the introgressed mitochondrial genome among all known species closely related to C. lapponica. We therefore suggest that the putative introgression event is ancient and the source species is either extinct or currently outside the geographic range of C. lapponica explored in this study. The observed DNA sequence variation also suggests that a host-plant shift from willow to birch has occurred recently and independently in each of the three birch-feeding populations. This emphasizes further the relative ease with which these beetles can escape their ancestral host-plant specialization on willow, but shows at the same time that host-plant shifts are highly constrained, as they only occur between willow and birch.

Reduced population control of an insect pest in managed willow monocultures.

BACKGROUND: There is a general belief that insect outbreak risk is higher in plant monocultures than in natural and more diverse habitats, although empirical studies investigating this relationship are lacking. In this study, using density data collected over seven years at 40 study sites, we compare the temporal population variability of the leaf beetle Phratora vulgatissima between willow plantations and natural willow habitats. METHODOLOGY/PRINCIPAL FINDINGS: The study was conducted in 1999-2005. The density of adult P. vulgatissima was estimated in the spring every year by a knock-down sampling technique. We used two measures of population variability, CV and PV, to compare temporal variations in leaf beetle density between plantation and natural habitat. Relationships between density and variability were also analyzed to discern potential underlying processes behind stability in the two systems. The results showed that the leaf beetle P. vulgatissima had a greater temporal population variability and outbreak risk in willow plantations than in natural willow habitats. We hypothesize that the greater population stability observed in the natural habitat was due to two separate processes operating at different levels of beetle density. First, stable low population equilibrium can be achieved by the relatively high density of generalist predators observed in natural stands. Second, stable equilibrium can also be imposed at higher beetle density due to competition, which occurs through depletion of resources (plant foliage) in the natural habitat. In willow plantations, competition is reduced mainly because plants grow close enough for beetle larvae to move to another plant when foliage is consumed. CONCLUSION/SIGNIFICANCE: To our knowledge, this is the first empirical study confirming that insect pest outbreak risk is higher in monocultures. The study suggests that comparative studies of insect population dynamics in different habitats may improve our ability to predict insect pest outbreaks and could facilitate the development of sustainable pest control in managed systems.

Detection of Anoplophora glabripennis (Coleoptera: Cerambycidae) larvae in different host trees and tissues by automated analyses of sound-impulse frequency and temporal patterns.

Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae), an invasive pest quarantined in the United States, is difficult to detect because the larvae feed unseen inside trees. Acoustic technology has potential for reducing costs and hazards of tree inspection, but development of practical methods for acoustic detection requires the solution of technical problems involving transmission of resonant frequencies in wood and high background noise levels in the urban environments where most infestations have occurred. A study was conducted to characterize sounds from larvae of different ages in cambium, sapwood, and heartwood of bolts from three host tree species. Larval sounds in all of the tested trees and tissues consisted primarily of trains of brief, 3-10-ms impulses. There were no major differences in the spectral or temporal pattern characteristics of signals produced by larvae of different ages in each tissue, but larval sounds in sapwood often had fewer spectral peaks than sounds in cambium and heartwood. A large fraction, but not all background sounds could be discriminated from larval sounds by automated spectral analyses. In 3-min recordings from infested bolts, trains containing impulses in patterns called bursts occurred frequently, featuring 7-49 impulses separated by small intervals. Bursts were rarely detected in uninfested bolts. The occurrence of bursts was found to predict infestations more accurately than previously used automated spectral analyses alone. Bursts and other features of sounds that are identifiable by automated techniques may ultimately lead to improved pest detection applications and new insight into pest behavior.

Predator diversity and identity drive interaction strength and trophic cascades in a food web.

Declining predator diversity may drastically affect the biomass and productivity of herbivores and plants. Understanding how changes in predator diversity can propagate through food webs to alter ecosystem function is one of the most challenging ecological research topics today. We studied the effects of predator removal in a simple natural food web in the Sierra Nevada mountains of California (USA). By excluding the predators of the third trophic level of a food web in a full-factorial design, we monitored cascading effects of varying predator diversity and composition on the herbivorous beetle Chrysomela aeneicollis and the willow Salix orestera, which compose the first and second trophic levels of the food web. Decreasing predator diversity increased herbivore biomass and survivorship, and consequently increased the amount of plant biomass consumed via a trophic cascade. Despite this simple linear mean effect of diversity on the strength of the trophic cascade, we found additivity, compensation, and interference in the effects of multiple predators on herbivores and plants. Herbivore survivorship and predator-prey interaction strengths varied with predator diversity, predator identity, and the identity of coexisting predators. Additive effects of predators on herbivores and plants may have been driven by temporal niche separation, whereas compensatory effects and interference occurred among predators with a similar phenology. Together, these results suggest that while the general trends of diversity effects may appear linear and additive, other information about species identity was required to predict the effects of removing individual predators. In a community that is not temporally well-mixed, predator traits such as phenology may help predict impacts of species loss on other species. Information about predator natural history and food web structure may help explain variation in predator diversity effects on trophic cascades and ecosystem function.

Mollusc grazing limits growth and early development of the old forest lichen Lobaria pulmonaria in broadleaved deciduous forests.

THIS STUDY AIMS: (1) to quantify mollusc grazing on juvenile and mature thalli of the foliose epiphytic lichen Lobaria pulmonaria, and (2) to test the hypothesis inferring a herbivore defensive role of lichen depsidones in forests with indigenous populations of lichen-feeding molluscs. Lichens were transplanted in shaded and less shaded positions in each of two calcareous broadleaved deciduous forests, one poor in lichens, one with a rich Lobarion community. Preventing the access of molluscs significantly reduced the loss of juvenile L. pulmonaria, particularly in the naturally lichen-poor forest. Molluscs also severely grazed mature thalli in the lichen-poor forest, especially thalli placed under the more shading canopies. Furthermore, reducing the natural concentration of depsidones by pre-rinsing with acetone increased subsequent grazing significantly, showing that lichen depsidones function as herbivore defence in natural habitats. Our results suggest that mollusc grazing may play important roles in shaping the epiphytic vegetation in calcareous deciduous forests, and that recently established juvenile L. pulmonaria thalli seem to be particularly vulnerable.

Mutualism in a community context: the positive feedback between an ant-aphid mutualism and a gall-making midge.

Although mutualisms are widespread and often described in natural history accounts, their ecological influences on other community members remain largely unexplored. Many of these influences are likely a result of indirect effects. In this field study, we investigated the indirect effects of an ant-aphid mutualism on the abundance, survival rates and parasitism rates of a co-occurring herbivore. Rabdophaga salicisbrassicoides (Diptera: Cecidomyiidae) induces rosette galls on the developing shoots of Salix exigua trees, and populations can reach outbreak densities (up to 1,000 galls/stem) in central Washington State (USA). Ant-tended aphids feed on these same stems and often feed on gall tissue. In this study we used a combination of manipulative experiments and observational surveys to test the hypothesis that the abundances of aphids, ants, and galls have positive and reciprocal effects on one another, in a manner that would create a positive feedback loop in population growth. In addition, we examined whether the combined presence of ants and aphids reduces parasitism rates for the gallers. In support of the positive feedback loop hypothesis, aphids enjoyed higher population growth rates in the presence of ants and galls, the presence of ants and aphids resulted in increased abundance of galls, and the abundances of ants, aphids and galls were all positively correlated with one another. However, the mechanism underlying the positive effect of ants and aphids on galler density remains unknown, as the mutualism did not affect parasitism rates. More broadly, this study demonstrates that mutualisms can have significant and complex indirect effects on community and population ecology.

Field evaluations of systemic insecticides for control of Anoplophora glabripennis (Coleoptera: Cerambycidae) in China.

Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae), a pest native to China and Korea, was discovered in North America in 1996. Currently, the only reliable strategy available for eradication and control is to cut and chip all infested trees. We evaluated various doses of the systemic insecticides azadirachtin, emamectin benzoate, imidacloprid, and thiacloprid for control of A. glabripennis in naturally infested elms (Ulmus spp.), poplars (Populus spp.), and willows (Salix spp. ) in China between 2000 and 2002. Significantly more dead A. glabripennis adults were found beneath elm and poplar trees treated with imidacloprid (in 2000 and 2001) or thiacloprid (in 2001) and beneath willow trees injected with imidacloprid or thiacloprid (in 2002) compared with control trees. In 2000, 4 mo after injection, the density of live A. glabripennis was significantly reduced in poplar trees treated with imidacloprid (90%) and in willow trees treated with imidacloprid (83%) or emamectin benzoate (71%) compared with controls. In 2001, 9 mo after injection, the density of live A. glabripennis was significantly reduced in poplar (76%) and willow (45%) trees treated with imidacloprid compared with control trees. Similarly, percentage mortality of all life stages of A. glabripennis feeding within trees was significantly higher on poplar trees 4 mo after injection with imidacloprid (64%) in 2000 and on elms (55%) and poplars (63%) 9 mo after injection with imidacloprid in 2001 compared with control trees. Imidacloprid residue levels in leaves and twigs collected at various times from 1 d to 9 mo after injection ranged from 0.27 to 0.46 ppm. Injecting A. glabripennis-infested trees with imidacloprid can result in significant mortality of adults during maturation feeding on leaves and twigs and of all life stages feeding within infested trees. Imidacloprid is translocated rapidly in infested trees and is persistent at lethal levels for several months. Although, injection with imidacloprid does not provide complete control of A. glabripennis, systemic insecticides may prove useful as part of an integrated eradication or management program.

Willow (Salix fragilis Linn.): A multipurpose tree species under pest attack in the cold desert of Lahaul valley, northwestern Himalaya, India.

Salix fragilis is the most common willow species grown extensively under the indigenous agroforestry system in the cold desert of Lahaul valley located in the northwestern Himalayas, India. Presently, this tree is under severe pest attack, and other infections have made its survival in the area questionable. This deciduous multipurpose tree species provides vegetation cover to the barren landscape of Lahaul and is a significant contributor of fuel and fodder to the region. This study is a detailed profile of the plant in three villages within this region: Khoksar, Jahlma, and Hinsa. The willow provided 69.5%, 29%, and 42% of the total fuelwood requirements of Jahlma, Khoksar, and Hinsa respectively. A striking observation was that only 30.0 +/- 20.1% trees were healthy: 55.2 +/- 16.1% of the willows have dried up and 14.8 +/- 6.1% were in drying condition due to a combination of pest infestation and infection. To sustain this cultivation of willow under the existing agroforestry system in the region, we recommend that locally available wild species and other established varieties of willow growing in similar regions of the Himalayas be introduced on a trial basis.

Habitat difference in abundance of willow leaf beetle Phratora vulgatissima (Coleoptera: Chrysomelidae): plant quality or natural enemies?

Herbivorous insects are influenced by both 'bottom-up' forces mediated through host plants and 'top-down' forces from natural enemies. Few studies have tried to evaluate the relative importance of the two forces in determining the abundance of insects. The leaf beetle Phratora vulgatissima Linnaeus sometimes occurs at high densities and severely damages the willow Salix cinerea in forest habitats. For willows growing in open agricultural landscapes (farmland S. cinerea), the leaf beetle generally occurs at low densities and plants receive little damage. The purpose of the present study was to evaluate the relative importance of host plant quality and natural enemies behind the observed difference in P. vulgatissima abundance. Female egg-laying and larval performance (growth and survival) were studied on caged willow branches in the field to investigate if plant quality differs between S. cinerea trees growing in forest and farmland habitats. The survival of eggs exposed to natural enemies was examined to see if predation could explain the low abundance of leaf beetles on farmland willows. The results indicated no difference in plant quality; female egg laying and larval performance did not differ between the forest and the farmland. However, heteropteran predators (true bugs) were more abundant, and the survival of eggs was lower, on plants in the farmland habitat than in the forest habitat. The data suggest that the low abundance of P. vulgatissima on farmland willows could not be explained by a poor quality of plants, but more likely by high predation from heteropterans.