bark beetle Dotaz Zobrazit nápovědu
Tree-killing bark beetles are major disturbance agents affecting coniferous forest ecosystems. The role of environmental conditions on driving beetle outbreaks is becoming increasingly important as global climatic change alters environmental factors, such as drought stress, that, in turn, govern tree resistance. Furthermore, dynamics between beetles and trees are highly nonlinear, due to complex aggregation behaviors exhibited by beetles attacking trees. Models have a role to play in helping unravel the effects of variable tree resistance and beetle aggregation on bark beetle outbreaks. In this article we develop a new mathematical model for bark beetle outbreaks using an analogy with epidemiological models. Because the model operates on several distinct time scales, singular perturbation methods are used to simplify the model. The result is a dynamical system that tracks populations of uninfested and infested trees. A limiting case of the model is a discontinuous function of state variables, leading to solutions in the Filippov sense. The model assumes an extensive seed-bank so that tree recruitment is possible even if trees go extinct. Two scenarios are considered for immigration of new beetles. The first is a single tree stand with beetles immigrating from outside while the second considers two forest stands with beetle dispersal between them. For the seed-bank driven recruitment rate, when beetle immigration is low, the forest stand recovers to a beetle-free state. At high beetle immigration rates beetle populations approach an endemic equilibrium state. At intermediate immigration rates, the model predicts bistability as the forest can be in either of the two equilibrium states: a healthy forest, or a forest with an endemic beetle population. The model bistability leads to hysteresis. Interactions between two stands show how a less resistant stand of trees may provide an initial toe-hold for the invasion, which later leads to a regional beetle outbreak in the resistant stand.
- MeSH
- biologické modely * MeSH
- brouci fyziologie MeSH
- epidemický výskyt choroby * MeSH
- kůra rostlin parazitologie MeSH
- nemoci rostlin parazitologie MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
Windfelled Norway spruce (Picea abies) trees play a crucial role in triggering large-scale outbreaks of the European spruce bark beetle Ips typographus. Outbreak management therefore strives to remove windfelled trees to reduce the risk of outbreaks, a measure referred to as sanitation logging (SL). Although this practice has been traditionally applied, its efficiency in preventing outbreaks remains poorly understood. We used the landscape simulation model iLand to investigate the effects of different spatial configurations and intensities of SL of windfelled trees on the subsequent disturbance by bark beetles. We studied differences between SL applied evenly across the landscape, focused on the vicinity of roads (scenario of limited logging resources) and concentrated in a contiguous block (scenario of spatially diversified management objectives). We focused on a 16 050 ha forest landscape in Central Europe. The removal of >80% of all windfelled trees is required to substantially reduce bark beetle disturbances. Focusing SL on the vicinity of roads created a "fire break effect" on bark beetle spread, and was moderately efficient in reducing landscape-scale bark beetle disturbance. Block treatments substantially reduced outbreaks in treated areas. Leaving parts of the landscape untreated (e.g., conservation areas) had no significant amplifying effect on outbreaks in managed areas. Climate change increased bark beetle disturbances and reduced the effect of SL. Our results suggest that past outbreak management methods will not be sufficient to counteract climate-mediated increases in bark beetle disturbance.
Bark beetles vector symbiotic fungal species into their host trees during mass attacks. The symbiotic relationship with blue stain fungi of the Ascomycetes, including genera of Endoconidiophora (syn. = Ceratocystis), promotes successful establishment whereby the microbes help to overcome the host trees' defence and degrade toxic resins. This is the first study to evaluate both the volatile emissions from an insect-associated blue stain fungus over time and the insect response in a field trapping experiment. Volatile emissions from isolates of Endoconidiophora rufipennis (ER) were collected by solid-phase microextraction (SPME) and analysed by gas chromatography-mass spectroscopy (GC-MS) over a period of 30 days. This virulent North American fungus is closely related to E. polonica, a symbiotic fungus known from Eurasian spruce bark beetle Ips typographus.Nine volatiles were emitted by ER in substantial amounts: isoamyl acetate, sulcatone, 2-phenethyl acetate, geranyl acetone, geranyl acetate, citronellyl acetate, (R)- and (S)-sulcatol, and (R)-sulcatol acetate. A late peaking compound was geranyl acetone. In the field trapping experiment, three of the fungal volatiles (geranyl acetone, 2-phenethyl acetate and sulcatone) were tested in combination with a synthetic aggregation pheromone for I. typographus. Traps with geranyl acetone attracted lower numbers of I. typographus compared to traps with 2-phenethyl acetate, sulcatone or the pheromone alone as a control. The results showed that geranyl acetone acts as an anti-attractant and may act naturally on I. typographus as a cue from an associated fungus to signal an overexploited host.
- MeSH
- Ascomycota * fyziologie MeSH
- brouci * fyziologie MeSH
- feromony metabolismus MeSH
- kůra rostlin metabolismus MeSH
- nosatcovití * mikrobiologie MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
The spectrum of Mesostigmata mite species that are phoretic on the bark beetle Ips typographus has been well described. However, phoretic mite abundance has mostly been quantified by researchers who used only a single method for capturing bark beetles: pheromone traps. We therefore compared mite abundance using two beetle-capture methods. At a single location with high numbers of I. typographus in the eastern Czech Republic in 2013, beetles were collected with pheromone traps and from infested logs placed in emergence traps. In total 29,589 I. typographus beetles were captured using the two methods. Mite abundance was assessed on 2400 beetles from pheromone traps and on 955 beetles from emergence traps; in total 5805 phoretic mesostigmatid mites were detected. Six species of phoretic mites were captured using pheromone traps and four species using emergence traps. The number of phoretic mites per beetle was higher for beetles captured in emergence traps than for beetles captured in pheromone traps. The most abundant mite species overall were Dendrolaelaps quadrisetus, Uroobovella ipidis, and Trichouropoda polytricha. The seasonal dynamics of phoretic mites paralleled the seasonal dynamics of their hosts.
- MeSH
- feromony MeSH
- kůra rostlin MeSH
- nosatcovití * MeSH
- roční období * MeSH
- roztoči * MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- Geografické názvy
- Česká republika MeSH
Bark beetles kill apparently vigorous conifers during epidemics by means of pheromone-mediated aggregation. During non-endemic conditions the beetles are limited to use trees with poor defense, like wind-thrown. To find olfactory cues that help beetles to distinguish between trees with strong or weak defense, we collected volatiles from the bark surface of healthy felled or standing Picea abies trees. Furthermore, living trees were treated with methyl jasmonate in order to induce defense responses. Volatiles were analyzed by combined gas chromatography and electroantennographic detection (GC-EAD) on Ips typographus antennae. Compounds eliciting antennal responses were characterized by single sensillum recording for identification of specific olfactory sensory neurons (OSN). Release of monoterpene hydrocarbons decreased, while oxygenated compounds increased, from spring to early summer in felled trees. In both beetle sexes particular strong EAD activity was elicited by trace amounts of terpene alcohols and ketones. 4-Thujanol gave a very strong response and the absolute configuration of the tested natural product was assigned to be (+)-trans-(1R,4S,5S)-thujanol by stereoselective synthesis and enantioselective gas chromatography. One type of OSN responded to all ketones and five other OSN were characterized by the type of compounds that elicited responses. Three new OSN classes were found. Of the eight EAD-active compounds found in methyl jasmonate-treated bark, the known anti-attractant 1,8-cineole was the one most strongly induced. Our data support the hypothesis that highly active oxygenated host volatiles could serve as positive or negative cues for host selection in I. typographus and in other bark beetles.
- MeSH
- acetáty farmakologie MeSH
- brouci fyziologie MeSH
- cyklopentany farmakologie MeSH
- elektrofyziologické jevy účinky léků MeSH
- kůra rostlin chemie účinky léků metabolismus MeSH
- monoterpeny chemická syntéza chemie farmakologie MeSH
- oxylipiny farmakologie MeSH
- plynová chromatografie s hmotnostně spektrometrickou detekcí MeSH
- smrk chemie metabolismus MeSH
- stereoizomerie MeSH
- styren chemie farmakologie MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
Bark beetles are destructive insect pests known to form symbioses with different fungal taxa, including yeasts. The aim of this study was to (1) determine the prevalence of the rare yeast Hyphopichia heimii in bark beetle frass from wild olive trees in South Africa and to (2) predict the potential interaction of this yeast with trees and bark beetles. Twenty-eight culturable yeast species were isolated from frass in 35 bark beetle galleries, including representatives of H. heimii from nine samples. Physiological characterization of H. heimii isolates revealed that none was able to degrade complex polymers present in hemicellulose; however, all were able to assimilate sucrose and cellobiose, sugars associated with an arboreal habitat. All isolates were able to produce the auxin indole acetic acid, indicative of a potential symbiosis with the tree. Sterol analysis revealed that the isolates possessed ergosterol quantities ranging from 3.644 ± 0.119 to 13.920 ± 1.230 mg/g dry cell weight, which suggested that H. heimii could serve as a source of sterols in bark beetle diets, as is known for other bark beetle-associated fungi. In addition, gas chromatography-mass spectrometry demonstrated that at least one of the isolates, Hyphopichia heimii CAB 1614, was able to convert the insect pheromone cis-verbenol to the anti-aggregation pheromone verbenone. This indicated that H. heimii could potentially influence beetle behaviour. These results support the contention of a tripartite symbiosis between H. heimii, olive trees, and bark beetles.
- MeSH
- brouci * mikrobiologie fyziologie MeSH
- feromony metabolismus MeSH
- kůra rostlin mikrobiologie MeSH
- kvasinky MeSH
- nosatcovití * MeSH
- Olea * MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
The severity and spatial extent of bark-beetle outbreaks substantially increased in recent decades worldwide. The ongoing controversy about natural forest recovery after these outbreaks highlights the need for individual-based long-term studies, which disentangle processes driving forest regeneration. However, such studies have been lacking. To fill this gap, we followed the fates of 2,552 individual seedlings for 12 years after a large-scale bark-beetle outbreak that caused complete canopy dieback in mountain Norway spruce (Picea abies) forests in southeast Germany. We explore the contribution of advance, disturbance-related, and post-disturbance regeneration to forest recovery. Most seedlings originated directly within the three-year dieback of canopy trees induced by bark-beetle outbreak. After complete canopy dieback, the establishment of new seedlings was minimal. Surprisingly, advance regeneration formed only a minor part of all regeneration. However, because it had the highest survival rate, its importance increased over time. The most important factor influencing the survival of seedlings after disturbance was their height. Survival was further modified by microsite: seedlings established on dead wood survived best, whereas almost all seedlings surrounded by graminoids died. For 5 cm tall seedlings, annual mortality ranged from 20 to 50% according to the rooting microsite. However, for seedlings taller than 50 cm, annual mortality was below 5% at all microsites. While microsite modified seedling mortality, it did not affect seedling height growth. A model of regeneration dynamics based on short-term observations accurately predicts regeneration height growth, but substantially underestimates mortality rate, thus predicting more surviving seedlings than were observed. We found that P. abies forests were able to regenerate naturally even after severe bark-beetle outbreaks owing to advance and particularly disturbance-related regeneration. This, together with microsite-specific mortality, yields structurally and spatially diverse forests. Our study thus highlights the so far unrecognized importance of disturbance-related regeneration for stand recovery after bark-beetle outbreaks.
- MeSH
- brouci fyziologie MeSH
- býložravci * MeSH
- lesy MeSH
- populační dynamika MeSH
- semenáček fyziologie MeSH
- smrk fyziologie MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Geografické názvy
- Německo MeSH
The enzyme glucose-6-phosphate dehydrogenase (G6PD) of the bark beetle Ips typographus is derived from a gene that includes eight exons and spans over 7100 nucleotides (nt). By means of two transcription starts, the gene generates two mRNA isoforms that are present in similar amounts in the larvae, pupae and adults. The A isoform includes exon IA of 115 nt, which is followed by intron 1a extending to position 3457 of the gene. The B mRNA isoform begins with exon IB (100 nt) that occupies positions 3291-3390 within the 1a intron. Exons II to VII are included in both mRNA isoforms. The gene contains 31.6% (36.5% in the translated region) of the GC nucleotides. Two transcription starts and the exon/intron organization distinguish bark beetle G6PD from the homologous genes known in other insects. Two enzyme variants were detected in the protein extracts of individual bark beetles but their relationship to the A and B mRNA isoforms is uncertain.
- MeSH
- brouci enzymologie genetika MeSH
- financování organizované MeSH
- genom hmyzu MeSH
- glukosa-6-fosfátdehydrogenasa genetika MeSH
- hmyzí geny MeSH
- komplementární DNA MeSH
- konzervovaná sekvence MeSH
- messenger RNA MeSH
- molekulární evoluce MeSH
- molekulární sekvence - údaje MeSH
- počátek transkripce MeSH
- regulace genové exprese enzymů MeSH
- sekvence aminokyselin MeSH
- sekvence nukleotidů MeSH
- sekvenční analýza DNA MeSH
- Southernův blotting MeSH
- vývojová regulace genové exprese MeSH
- zvířata MeSH
- Check Tag
- mužské pohlaví MeSH
- ženské pohlaví MeSH
- zvířata MeSH
BACKGROUND: Bark beetles are major pests of conifer forests, and their behavior is primarily mediated via olfaction. Targeting the odorant receptors (ORs) may thus provide avenues towards improved pest control. Such an approach requires information on the function of ORs and their interactions with ligands, which is also essential for understanding the functional evolution of these receptors. Hence, we aimed to identify a high-quality complement of ORs from the destructive spruce bark beetle Ips typographus (Coleoptera, Curculionidae, Scolytinae) and analyze their antennal expression and phylogenetic relationships with ORs from other beetles. Using 68 biologically relevant test compounds, we next aimed to functionally characterize ecologically important ORs, using two systems for heterologous expression. Our final aim was to gain insight into the ligand-OR interaction of the functionally characterized ORs, using a combination of computational and experimental methods. RESULTS: We annotated 73 ORs from an antennal transcriptome of I. typographus and report the functional characterization of two ORs (ItypOR46 and ItypOR49), which are responsive to single enantiomers of the common bark beetle pheromone compounds ipsenol and ipsdienol, respectively. Their responses and antennal expression correlate with the specificities, localizations, and/or abundances of olfactory sensory neurons detecting these enantiomers. We use homology modeling and molecular docking to predict their binding sites. Our models reveal a likely binding cleft lined with residues that previously have been shown to affect the responses of insect ORs. Within this cleft, the active ligands are predicted to specifically interact with residues Tyr84 and Thr205 in ItypOR46. The suggested importance of these residues in the activation by ipsenol is experimentally supported through site-directed mutagenesis and functional testing, and hydrogen bonding appears key in pheromone binding. CONCLUSIONS: The emerging insight into ligand binding in the two characterized ItypORs has a general importance for our understanding of the molecular and functional evolution of the insect OR gene family. Due to the ecological importance of the characterized receptors and widespread use of ipsenol and ipsdienol in bark beetle chemical communication, these ORs should be evaluated for their potential use in pest control and biosensors to detect bark beetle infestations.
Coniferous forests cover extensive areas of the boreal and temperate zones. Owing to their primary production and C storage, they have an important role in the global carbon balance. Forest disturbances such as forest fires, windthrows or insect pest outbreaks have a substantial effect on the functioning of these ecosystems. Recent decades have seen an increase in the areas affected by disturbances in both North America and Europe, with indications that this increase is due to both local human activity and global climate change. Here we examine the structural and functional response of the litter and soil microbial community in a Picea abies forest to tree dieback following an invasion of the bark beetle Ips typographus, with a specific focus on the fungal community. The insect-induced disturbance rapidly and profoundly changed vegetation and nutrient availability by killing spruce trees so that the readily available root exudates were replaced by more recalcitrant, polymeric plant biomass components. Owing to the dramatic decrease in photosynthesis, the rate of decomposition processes in the ecosystem decreased as soon as the one-time litter input had been processed. The fungal community showed profound changes, including a decrease in biomass (2.5-fold in the litter and 12-fold in the soil) together with the disappearance of fungi symbiotic with tree roots and a relative increase in saprotrophic taxa. Within the latter group, successive changes reflected the changing availability of needle litter and woody debris. Bacterial biomass appeared to be either unaffected or increased after the disturbance, resulting in a substantial increase in the bacterial/fungal biomass ratio.
- MeSH
- biomasa MeSH
- brouci fyziologie MeSH
- houby klasifikace izolace a purifikace MeSH
- lesy * MeSH
- půdní mikrobiologie * MeSH
- smrk MeSH
- stromy MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
