Pathogens of Ips amitinus: new species and comparison with Ips typographus

Ips amitinus and I. typographus are two serious pests of spruce in Europe, have similar bionomics and are likely to occur and meet on the same host trees. We therefore hypothesized that the two species support similar levels of similar pathogens. To test this hypothesis, we collected mature beetles from three trap trees at each of eight study sites and determined beetle numbers and pathogen infection levels. In total, 938 mature I. amitinus beetles and 3435 of I. typographus were dissected; five pathogens, as well as intestinal nematodes and endoparasitoids, were detected. The neogregarine Mattesia schwenkei is reported here for the first time as a new pathogen in 9.4% of I. amitinus individuals at one site. Average infection levels of most pathogens (Chytridiopsis typographi, Gregarina typographi, Mattesia schwenkei and parasitoids) were significantly higher in I. typographus than in I. amitinus. Metschnikowia typographi was confirmed only in Ips amitinus, while the microsporidium of Nosema typographi occurred only in I. typographus. Within‐season increases in G. typographi infection levels were documented in Ips amitinus.     

Occurrence of pathogens in Ips typographus (Coleoptera: Curculionidae) and in other spruce bark beetles from the wilderness reserve Dürrenstein (Lower Austria)

The study presents new data on spatial distribution of bark beetle pathogens, on changes in frequency over several years and on their prevalence during different time periods within a year from several locations within the wilderness reserve Dürrenstein (Lower Austria). The occurrence of pathogens was investigated in Ips typographus (during five years), in Pityogenes chalcographus (during two years) and in Ips amitinus (in one year). In total, seven pathogen species could be detected in I. typographus. The most dominant pathogen species were the Ips typographus-Entomopoxvirus (ItEPV), the sporozoan species Gregarina typographi and the microsporidium Chytridiopsis typographi; the latter two pathogen species were recorded every year and at about similar high (G. typographi) or low (C. typographi) rates, the ItEPV in strongly varying rates. The neogregarine Mattesia cf. schwenkei and the two microsporidia Nosema typographi and Unikaryon montanum were found in I. typographus only sporadically and the rhizopodan species Malamoeba scolyti was found once. The number of infected males and females was relatively similar with almost all pathogen species in most of the years except U. montanum, which occurred exclusively in females. Three pathogen species were recorded in P. chalcographus which were Gregarina typographi, Mattesia cf. schwenkei and Chytridiopsis typographi. Two pathogen species were observed in I. amitinus, Gregarina typographi and Chytridiopsis typographi.     

On the pathogens of the spruce bark beetle Ips typographus (Coleoptera: Scolytinae) in the Western Carpathians

Pathogens of spruce bark beetle Ips typographus were compared at eleven sites in Slovakia (the Western Carpathians). Seven different pathogen species were recorded: protozoan species Chytridiopsis typographi, Gregarina typographi, Malamoeba scolyti, nematodes of the genus Neoparasitylenchus and one unidentified nematode species. Presence of the entomopathogenic fungus Beauveria bassiana was also observed as well as parasitization by hymenopteran parasitoids. High infection rate of G. typographi and the nematode Neoparasitylenchus was detected in almost all sites and lethal impact of M. scolyti by massive infections was observed. The beetles from seven sites were screened for endosymbiotic bacteria Wolbachia, however, with no positive result.     

A host monoterpene influences Ips typographus (Coleoptera: Curculionidae,Scolytinae) responses to its aggregation pheromone

1 Host tree terpenes can influence attraction of conifer‐infesting bark beetles to their aggregation pheromones, and both synergistic and inhibitory effects have been reported. 2 We tested a gradient of ratios of (–)‐α‐pinene, the predominant monoterpene in Norway spruce, to the pheromone of Ips typographus, a major pest of Norway spruce. 3 Attraction of I. typographus increased as the release rate of (–)‐α‐pinene increased. The two highest (–)‐α‐pinene : pheromone ratios (526 : 1 and 2595 : 1) attracted twice as many I. typographus as pheromone alone, whereas low to intermediate ratios (56 : 1, 274 : 1) did not differ from pheromone alone. 4 Our results are in agreement with a proposed model, which suggests that bark beetles display unique response profiles to host terpenes depending on the physiological condition of the host trees that they typically colonize. Ips typographus, which is an aggressive species capable of colonizing and killing healthy trees, showed an increased attraction to monoterpene : pheromone ratios, and this may be high enough to inhibit attraction of less aggressive beetle species typically colonizing dead, dying or stressed trees. 5 Attraction of associates of I. typographus was also modified by (–)‐α‐pinene. Ips duplicatus, a competitor of I. typographus, showed increased attraction to the pheromone of I. typographus across all concentrations of (–)‐α‐pinene.     

The comparative prevalence and demographic impact of two pathogens in swarming Ips typographus adults: a quantitative analysis of long term trapping data

• 1 Adult Ips typographus were collected using pheromone traps at a locality in the eastern part of Austria between 1995 and 2004. The occurrence of two pathogens, Gregarina typographi and Chytridiopsis typographi, was determined throughout the period of beetle swarming activities. Weekly and annual data sets were then analysed by smoothing statistical techniques and epidemiological models.
• 2 The pathogens spread differently within the beetle population with respect to their biological characteristics: infectious forms of C. typographi were immediately available after their development in the insect's gut, but not those of G. typographi.
• 3 Both of the pathogens had a low prevalence in swarming beetles, especially C. typographi, and there was no evidence of a between‐year or within‐year epidemiological process. Conversely, it was shown that G. typographi has a positive effect on the rate of increase of trapped beetles.
• 4 Fitting a nonlinear model to the data suggested that: (i) this was due to a higher catch ability of beetles infected with G. typographi than of healthy beetles; (ii) when this effect is taken into account, G. typographi induces a specific within‐year low mortality in beetle populations; and (iii) beetle populations increase naturally within a year, despite their infection by both pathogens. No clear effect of C. typographi was detected in the trapped data set when the prevalence of this species was high in beetle populations collected from trees.
• 5 It is hypothesized that both pathogens induce different behavioural effects on their host, resulting in: (i) favouring the trapping of G. typographi‐infected beetles and (ii) hindering the capture of C. typographi‐infected individuals. This could be the result of both of the pathogens having an opposite effect on the flight abilities of beetles and/or on the beetles' response to the aggregation pheromones used in the traps.

     

Pathogens of the bark beetle Ips cembrae: microsporidia and gregarines also known from other Ips species

The objective of the current study was to identify pathogens of the large larch bark beetle, Ips cembrae, which is a secondary pest that has produced several local outbreaks across Europe in recent years. Beetles were collected from pheromone traps, trap trees and emergence traps (Larix decidua) during 2007 to 2011 at 10 study sites in central Europe. A total of 3379 mature and callow beetles were examined with a light microscope, and only two microsporidian pathogens [Chytridiopsis typographi and a diplokaryotic microsporidium (probably Nosema sp.)] and two gregarines (Gregarina typographi and Mattesia schwenkei) were found. Within the I. cembrae populations, the infection rate for C. typographi ranged from 2 to 58%. Nosema sp. occurred in only two beetles in 2007 (at two study sites). G. typographi was recorded only in Austria and Croatia and only in 1–2% of the beetles in those countries. Mattesia schwenkei was observed solely in Croatia in 0.6% of the beetles in that country. Only one fungal pathogen in the genus Fusarium was found and only in two mature beetles (0.7%) in 2010. The pathogen species found during our study of I. cembrae were very similar to the pathogens previously identified for Ips typographus. No species‐specific pathogen was detected.     

Pathogen's level and parasitism rate in Ips typographus at high population densities: importance of time

We compared the levels of pathogen infection in parental beetles, parasitism of the offspring, abundance of predators and breeding performance success of univoltine populations of Ips typographus in plots characterized by short‐term (2–3 years) outbreaks vs. those with long‐term (>10 years) outbreaks on two localities at ca. 1100 m altitude in the ?umava Mts. The numbers of I. typographus were high in all plots, whether the plots were characterized by long‐term outbreaks or short‐term outbreaks. The numbers of maternal galleries in the sample areas ranged from 300 to 400 per m². The density of parental beetle galleries, abundance of surviving specimens of I. typographus, and length of maternal galleries did not differ between plots. The short‐term outbreaks had only fewer ectoparasitoids of I. typographus and a lower percentage of parasitism and infection level of Mattesia schwenkei than the long‐term outbreaks even though the maternal gallery densities and beetle production were the same. The most mortality appeared to be caused by intraspecific larval competition, and the identical reproductive success in plots with short‐term and long‐term outbreaks indicates that the negative feedback resulting from parasitoids and entomopathogens does not substantially reduce beetle numbers. Although entomopathogenic fungi as Beauveria bassiana occur naturally in the galleries of spruce bark beetles, there was no evidence of its presence in the studied population. The low levels of predation and/or parasitism in both kinds of plots indicate that natural enemies did not play a significant role in reducing outbreak numbers of I. typographus.     

Infections with the ascomycete fungus Metschnikowia typographi sp.nov. in the bark beetles Ips typographus and Ips amitinus (Coleoptera, Scolytidae)

The ascomycete fungus Metschnikowia typographi sp.nov. is described. It infects the spruce bark beetles Ips typographus L. and Ips amitinus Eichl. Masses of vegetative cells and navicular asci (I. typographus 13-17 x 2 microns; I. amitinus 17-22 x 2 microns) were found in cells of the midgut epithelium and in the body cavity of infected beetles. Each ascus contains two needle-shaped ascospores flattened in the central part, 0.5-1.5 x 0.3 x 13-15 microns and pointed at both ends. The parasitic species of Metschnikowia, M. bicuspidata, M. artemiae, M. unicuspidata, M. wickerhami and M. typographi are discussed as a special group of the genus characterized by morphological characters.     

Size and shape changes of Ips typographus L. (Coleoptera: Scolytinae) in relation to population level

1 High intraspecific competition is known to occur during Ips typographus outbreaks, and is thought to be the main factor regulating epidemic populations by affecting beetle population productivity. However, little is known about the consequences of intraspecific competition on population quality during outbreaks, although it could have consequences on beetle population dynamics. 2 Ips typographus morphological variations among localities, years and beetle population levels were investigated in 10 Norway spruce (Picea abies) stands having various beetle damage intensities. Beetle size and shape estimators based on wing length, and using isometric size and log‐shape ratios, were employed. Field‐caught beetles were compared with beetles emerging from controlled breeding at different densities, performed in the laboratory. Beetles from this colony were also used to check the influence of breeding densities on the size estimator. 3 Size variations occurred among localities and years and were consistent with the epidemic or latent status of the beetle populations. Controlled breeding confirmed the negative effect of beetle densities encountered in the field on offspring size. Two hypotheses are formulated to explain this increase of intraspecific competition during an outbreak, but our data support the effect of host quality change between latent and epidemic populations. 4 Shape variations also occurred among localities but were unrelated to beetle population levels. No groups consistent with a geographical structure were found, suggesting low genetic variation for I. typographus populations in France.     

Nematodes associated with the double‐spined bark beetle Ips duplicatus (Coleoptera: Curculionidae) in central Europe

Ips duplicatus (Sahlberg) is an important forest pest in central Europe, but its nematode associates have seldom been studied. Therefore, nematodes associated with I. duplicatus were determined at three localities in the Czech Republic. The percentage of beetles with phoretic nematodes ranged from 18 to 65%. Micoletzkya buetschlii and other phoretic nematodes were found under elytra, on wings, and between body segments. The percentage of beetles with nematodes in the haemocoel ranged from 3 to 30%, and the nematodes included Contortylenchus diplogaster and Parasitylenchus cf. aculeatus. Juveniles of Parasitorhabditis obtusa (Fuchs 1915) were found in the intestines of 0–16% of the beetles. The most abundant species in I. duplicatus galleries were P. obtusa and M. buetschlii. Cryptaphelenchus sp., Parasitaphelenchus sp. and unidentified tylenchid juveniles also were found in the galleries. The percentage of beetles with nematodes was greater in the overwintering than in the offspring generation, and numbers of nematodes per gallery increased with gallery development.     

Effects of heat on the dispersal performance of Ips typographus

Under present climate conditions, Ips typographus (L.) is Europe's most critical disturbance agent for mature Norway spruce (Picea abies). With ongoing climate change, the bark beetle will most probably become more prominent as a pest. The aim of this study was to analyse the dispersal performance of I. typographus under various weather conditions, especially hot days with a maximum air temperature above 30°C. In a field study, marked bark beetles were released from breeding logs and could be retraced in traps distributed across the survey area. With daily collections of the trapped beetles, it was possible to analyse the flight activity and the average flight distance of the bark beetles during hot, moderate and cool days. The numbers of daily catches and the average flight distance during the hottest days (air temperature maximum ≥30°C) did not significantly differ from the moderate days (air temperature maximum ≥22°C and <30°C). The numbers of daily catches and the average flight distance during the cool days (air temperature maximum <22°C) were significantly lower than during hot and moderate days. The results give an insight on the dispersal capacity of I. typographus under climate change driven future conditions. Increased air temperatures do not seem to impair the flight performance of I. typographus. A small proportion of cool days during the swarming period even seems to favour dispersal of I. typographus.     

Performance of the tree‐killing bark beetles Ips typographus and Pityogenes chalcographus in non‐indigenous lodgepole pine and their historical host Norway spruce

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Fungi Vectored by the Bark Beetle Ips typographus Following Hibernation Under the Bark of Standing Trees and in the Forest Litter

The bark beetle Ips typographus has different hibernation environments, under the bark of standing trees or in the forest litter, which is likely to affect the beetle-associated fungal flora. We isolated fungi from beetles, standing I. typographus-attacked trees, and forest litter below the attacked trees. Fungal identification was done using cultural and molecular methods. The results of the two methods in detecting fungal species were compared. Fungal communities associated with I. typographus differed considerably depending on the hibernation environment. In addition to seven taxa of known ophiostomoid I. typographus-associated fungi, we detected 18 ascomycetes and anamorphic fungi, five wood-decaying basidomycetes, 11 yeasts, and four zygomycetes. Of those, 14 fungal taxa were detected exclusively from beetles that hibernated under bark, and six taxa were detected exclusively from beetles hibernating in forest litter. The spruce pathogen, Ceratocystis polonica, was detected occasionally in bark, while another spruce pathogen, Grosmannia europhioides, was detected more often from beetles hibernating under the bark as compared to litter. The identification method had a significant impact on which taxa were detected. Rapidly growing fungal taxa, e.g. Penicillium, Trichoderma, and Ophiostoma, dominated pure culture isolations; while yeasts dominated the communities detected using molecular methods. The study also demonstrated low frequencies of tree pathogenic fungi carried by I. typographus during its outbreaks and that the beetle does not require them to successfully attack and kill trees.     

Effect of different semiochemicals blends on spruce bark beetle,Ips typographus (Coleoptera: Scolytidae)

The spruce bark beetle, Ips typographus, is a recent new introduction to the Qilian Mountains of China. An outbreak of these beetles has infested over 0.03 million hectares of spruce forests in this area. Although primary attraction to volatiles has been clearly demonstrated for I. typographus, the existence and role of attraction to insect‐produced pheromones have been widely debated. Currently, commercial lures for I. typographus include only the volatiles ipsdienol, cis‐verbenol, trans‐verbenol, 2‐methyl‐3‐buten‐2‐ol and 2‐phenylethanol in Europe. Several potential pheromone candidates have been identified for I. typographus. Our GC–MS and GC–FID analyses volatiles from hindgut extracts of I. typographus in different attack phases demonstrated that the 2‐methyl‐3‐buten‐2‐ol, ipsdienol, cis‐verbenol and trans‐verbenol as major hindgut components, and ipsenol, 2‐phenylethanol, trans‐ myrtenol and verbenone as minor components. We tested various combinations of semiochemical candidates, to determine an optimal blend. Our results suggest that addition of 2‐methyl‐3‐buten‐2‐ol to either ipsenol alone, or to blends of ipsenol and other semiochemical candidates, significantly enhanced attraction of I. typographus. Therefore, a simple lure consisting of ipsenol and 2‐methyl‐3‐buten‐2‐ol would be an optimal blend of I. typographus in the Qilian Mountains, China. We conclude that this optimal semiochemical blend may provide an effective biological pest control method for use in forest ecosystem against I. typographus.     

Emergence patterns of univoltine and bivoltine Ips typographus (L.) populations and associated natural enemies

Control measures aiming at reducing bark beetle populations and preserving their natural enemies require a sound knowledge on their overwintering and emergence behaviour. These behavioural traits were investigated in univoltine and bivoltine populations of the European spruce bark beetle (Ips typographus [L.], Coleoptera: Scolytinae) and its predators and parasitoids over several consecutive years. In univoltine populations, roughly 50% of the bark beetles left their brood trees in fall together with most parasitoids and some significant predatory flies and beetles. In bivoltine populations, <10% of the second bark beetle generation emerged in fall and the remainder overwintered under the bark of their brood trees. Likewise, most predatory beetles and flies spent wintertime with their prey under the bark, while most parasitic wasps emerged in fall. The spring emergence of bivoltine predatory beetles was found to occur up to 3 weeks earlier than that of I. typographus, while that of the predatory flies and the parasitoids was delayed by up to 1 month. In univoltine populations, the bark beetles emerged several weeks prior to most antagonistic taxa. In the heat year 2003, three I. typographus generations were produced at the lower location, 36% of the third generation emerged in fall, while the proportions of overwintering predators remained largely the same as in previous years. Similar to their host, more parasitoids left their brood trees in fall after warm years. The results show that sanitation felling during winter probably kills most bark beetles in bivoltine populations, but also eliminates many natural enemies. In univoltine populations, sanitation felling might be less detrimental to both I. typographus and natural enemies because a fair fraction of their populations will already have left the trees before cutting. Warmer climates may affect the interactions of bark beetles and natural enemies and thus the impact of control measures.     

Field response of the northern spruce bark beetle Ips duplicatus (Sahlberg) (Coleoptera: Curculionidae,Scolytinae) to different combinations of synthetic pheromone with (−)‐α‐pinene and (+)‐limonene

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Exogenous application of methyl jasmonate elicits defenses in Norway spruce (Picea abies) and reduces host colonization by the bark beetle Ips typographus

The terpenoid and phenolic constituents of conifers have been implicated in protecting trees from infestation by bark beetles and phytopathogenic fungi, but it has been difficult to prove these defensive roles under natural conditions. We used methyl jasmonate, a well-known inducer of plant defense responses, to manipulate the biochemistry and anatomy of mature Picea abies (Norway spruce) trees and to test their resistance to attack by Ips typographus (the spruce bark beetle). Bark sections of P. abies treated with methyl jasmonate had significantly less I. typographus colonization than bark sections in the controls and exhibited shorter parental galleries and fewer eggs had been deposited. The numbers of beetles that emerged and mean dry weight per beetle were also significantly lower in methyl jasmonate-treated bark. In addition, fewer beetles were attracted to conspecifics tunneling in methyl jasmonate-treated bark. Stem sections of P. abies treated with methyl jasmonate had an increased number of traumatic resin ducts and a higher concentration of terpenes than untreated sections, whereas the concentration of soluble phenolics did not differ between treatments. The increased amount of terpenoid resin present in methyl jasmonate-treated bark could be directly responsible for the observed decrease in I. typographus colonization and reproduction.     

Characterization of fungal communities associated with the bark beetle Ips typographus varies depending on detection method, location, and beetle population levels

The Eurasian spruce bark beetle Ips typographus and their fungal associates can cause severe damage to Norway spruce forests. In this paper, by using both molecular and cultural methods, we compared fungal assemblages on bark beetles from different locations, characterized by different beetle population levels. Ips typographus was trapped in the western Alps in two outbreak and in two control areas. Sequencing of clone libraries of Internal Transcribed Spacer (ITS) identified 31 fungal Operational Taxonomic Units (OTUs), while fungal isolations yielded 55 OTUs. Only three OTUs were detected by both molecular and cultural methods indicating that both methods are necessary to adequately describe fungal richness. Fungal assemblages on insects from these four and from an additional 12 study sites differed among stands in response to varying ecological conditions and to the limited spreading ability of I. typographus. Ophiostomatoid fungi showed higher diversity in outbreak areas; the pathogenic Ophiostoma polonicum was relatively uncommon, while O. bicolor was the most abundant species. This result was not unexpected, as insects were trapped not at the peak but at the end of the outbreaks and supports the hypothesis of a temporal succession among Ophiostoma species. Ubiquitous endophytes of trees or common airborne fungi were present both in outbreak and in control areas. Wood decaying basidiomycetes were almost never detected on beetles. Yeasts were detected only by molecular analysis, and the OTUs detected matched those reported elsewhere in Europe and in the world, suggesting a very long association between some yeasts and bark beetles.     

Quantification of different yeasts associated with the bark beetle,Ips typographus,during its attack on a spruce tree

There were different amounts and types of yeasts associated with individuals ofIps typographus spruce bark beetles during different phases of their attack on a healthy spruce tree. The yeasts were isolated on Sabouraud agar medium in order to identify them and estimate their numbers.Hansenula holstii andCandida diddensii type yeasts were most frequently isolated. The increase in number of these two yeast types probably accounted for most of the total yeast increase found during the later attack phases of the bark beetles. Lesser amounts ofHansenula capsulata, Pichia pinus, Candida nitratophila, and twoCryptococcus type yeasts were also found.     

Monitoring of Ips typographus and Pityogenes chalcographus: influence of trapping site and surrounding landscape on catches

• 1 The influence of trapping site (i.e. fresh clear‐cuts) characteristics and habitat amount (i.e. area of stands that may hold breeding material) in the surrounding landscape on catches of the bark beetles Ips typographus (L.) and Pityogenes chalcographus (L.) in pheromone‐baited flight‐barrier monitoring traps was studied.
• 2 For the two species, the study investigated: (i) the extent of the variation in catches among trapping sites; (ii) the extent of this variation that can be explained by models including trapping site characteristics (clear‐cut size, percentage of spruce in the cut stand, altitude) and habitat amounts in the surrounding landscape; and (iii) the spatial scale at which beetles respond to the habitat amount in the landscape.
• 3 The variation in catches among trap sites was 15‐fold larger for I. typographus than for P. chalcographus. There was a positive relationship between the catches of I. typographus and (i) the percentage of the surrounding landscape covered by mature spruce forest at radii 500–4000 m and (ii) the percentage of spruce in stands cut when the clear‐cuts used as trapping sites were created. For P. chalcographus, only the second relationship could be demonstrated.
• 4 Thus, for monitoring of I. typographus: (i) several trapping sites per landscape are required; (ii) the amount of mature spruce forest around trapping sites needs to be considered when choosing trapping sites; and (iii) the trapping sites need to be standardized with respect to the percentage of spruce in the cut stand when fresh clear‐cuts are used. For P. chalcographus, fewer trapping sites per landscape are required and only the percentage of spruce in the cut stand needs to be considered.