Flight initiation and survival in the bark beetle Ips typographus (Coleoptera: Scolytidae) during the spring dispersal

Temperatures in the forest litter of Norway spruce Picea abies were recorded throughout the day to obtain environmental parameters that could be used to design realistic flight-activity experiments in the laboratory. Flight activity and survival were monitored electronically in plastic chambers where the conditions were controlled by an environmental chamber. Flight attempts of the bark beetle Ips typographus were initially lower in chambers with forest duff but were prolonged compared with those of beetles in chambers with a metal screen substrate. Small bark slabs and spruce twigs in the duff were utilized as food and extended the period of flight and survival. A thermal gradient in duff from 25° at the surface down to 13.8°C at a depth of 4 cm also slightly increased the survival of beetles compared with a constant 25°. A daily ambient temperature cycle as well as the duff thermal gradient increased the survival from about 3 d to more than 8 d. The latter length in the laboratory agreed with survival rates of caged beetles in a clearcut forest area, while beetles caged in the forest survival for more than 14 d. Temperatures were monitored at the duff surface of the caged beetles and compared with the catches of beetles that were attracted to a pheromone trap and collected with an electronic fraction collector. Information on flight and survival during the dispersal period is necessary to the design of ecologically sound management programs for control of bark beetles.     

Gallery construction and oviposition of the bark beetle Ips typographus (Coleoptera: Scolytidae) at different breeding densities

Abstract. 1. The bole of a Norway spruce, Picea abies (L.) Karst., was cut in 25 cm sections and infested in the laboratory with 2 or 8 females/dm² of Ips typographus (L.) and an equal number of males.
2. One log of each beetle density was dissected every second day, beginning 2 days after female introduction.
3. The oviposition rate was highest at the beginning of the breeding period for both densities and then declined, especially at the high density. Residence time is a useful approximation for the number of laid eggs in the beginning of the oviposition period or when the density is low.
4. Final gallery length and egg number per gallery were on average significantly smaller at density 8 than at density 2.
5. Linear relationships between total gallery length and number of egg niches were found to be similar for the two densities.
6. An estimate of the egg to adult mortality at different densities was found by using data from a field study that related gallery length to breeding density in attacked living trees, together with published relationships between density and egg niches or emergence of new adults.
7. It was concluded that both decreased oviposition rate and earlier re-emergence at higher densities contribute to a declining oviposition with increasing density. The final offspring production is futher reduced by lower survival due to larval competition as density increases.     

Host tree resistance influencing pheromone production in Ips typographus (Coleoptera: Scolytidae)

Analyses of volatiles in hindguts of Ips typgraphus males from different spruce trees and attack phases are reviewed. The composition of monoterpenes, and the chirality of α-pinene, have been determined in phloem samples. Relationships between compounds emanating from spruce trees and bark beetles, respectively, have been studied. Male beetles depend on their host tree for the production of pinene alcohols. The ratio between the pinene alcohols is almost constant in males boring in the same tree but can vary widely between males from different spruce trees. Very good correlations were found between some host tree monoterpene hydrocarbons and bark beetle produced pinene alcohols. The production of the essential pheromone component 2-methyl-3-buten-2-ol, was not correlated with the monoterpene content in the host trees, while the production of the other essential pheromone component, cis-verbenol, depends on the amount of the precursor, (−)-α-pinene in the phloem. Male beetles boring in a resistant spruce tree will continue to produce the pinene alcohols, including cis -verbenol, as long as the tree defends itself with resin.     

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.     

Ultrastructural study of the microsporidian chytridiopsis typographi (Chytridiopsida: Microspora) infecting the bark beetle,Ips typographus (Scolytidae: Coleoptera), with new data on spore dimorphism

Two types of sporogony of the microsporidian Chytridiopsis typographi in the midgut of adult bark beetle, Ips typographus, have been examined by means of light and electron microscopy. New data are reported on spore dimorphism and on the formation of pansporoblasts in two types of sporogony. Thin-walled spores, larger in size, are formed in a parasitophorous vacuole in the host columnar cells. Thick-walled spores are formed in a minimal vacuole in the host. The ultrastructure of the spore walls and the cyst wall are different from the organization in other microsporidia. Both spore types have identical internal structures and viable spores.     

Phylogeography and postglacial colonization routes of Ips typographus L. (Coleoptera, Scolytidae)

Ips typographus populations were analysed by enzyme electrophoresis and by sequence analysis in order to quantify the degree of population differentiation. Enzyme electrophoresis showed a high gene flow among all European populations. Analysis of single loci showed that aspartate aminotransferase-2 ( Aat-2 ) clustered the Scandinavian populations apart from the other populations whereas other enzyme loci showed no significant pattern. Analysis of mitochondrial DNA revealed eight haplotypes. The populations from Italy, Croatia and Belgium were the most polymorphic. Two haplotypes (I and II) were found in the majority of Central European populations. In the northern populations only one haplotype (I) was found. The Russian and Lithuanian populations had a particular haplotype (IV) that was not found in any of the other populations. In view of these data it is suggested that the population structure of I. typographus has been influenced by events which took place during and after the last ice age. Populations were forced into refugial areas in the south and in the area north of Moscow along with the host tree, Picea abies . P. abies had four refugial areas: the Apennine Alps, the Dinaric Alps, the Carpathian Alps and Kostroma, an area north of Moscow. With amelioration of the temperature, beetles spread after P. abies . According to the data presented here, I. typographus migrated from the Apennine and/or Dinaric Alps to the north. Whilst there is evidence for high gene flow among populations, bottleneck effects can still be detected in the north and also in the east. Beetles from the refugial area north of Moscow did not spread to Scandinavia or to the west like the host tree.     

The bark beetle Pityogenes chalcographus (L.) (Scolytidae) in living trees: reproductive success, tree mortality and interaction with Ips typographus

Abstract:  Tree-killing ability of Pityogenes chalcographus was experimentally investigated by baiting living spruce Picea abies with synthetic aggregation pheromone, thereby exposing them to beetle attack. Reproductive success was estimated by rearing beetles from stem sections taken from killed trees. The presence of Ips typographus on several killed trees allowed a comparison of reproductive success in the presence and absence of this species. Furthermore, the possibility that breeding material colonized by P. chalcographus may induce subsequent attacks by I. typographus on nearby trees was also studied. The tree killing ability of P. chalcographus was low as only 8% of the baited trees, attacked by P. chalcographus alone, were killed. Tree death was strongly related to the presence of I. typographus , which is in line with the association with aggressive wood-living fungi in this species. The reproductive success was low, with on average less than one daughter beetle produced per mother beetle. The success was significantly higher in trees also inhabited by I. typographus . Tree-parts colonized by P. chalcographus induced almost no attacks by I. typographus on nearby trees.     

Development and distribution of predators and parasitoids during two consecutive years of an Ips typographus (Col., Scolytidae) infestation

Abstract:   The development of the natural enemy complex, its within-tree distribution and the resulting mortalities imposed on bark beetles were investigated during two consecutive years (1994, 1995) at the peak of an Ips typographus infestation. For this reason bolts from infested spruce trees were incubated until the inhabiting insects had emerged. Some 17 000 antagonists were identified and found to belong to 16 predatory and 14 parasitic insect species. Among the predators the Dolichopodidae (Dip.) were most abundant, while among the parasitoids the Pteromalidae (Hym.) ranked first. Parasitoids preferred the upper tree parts, while predators were more abundant in the lower parts. Total bark beetle mortality was assessed based on the literature data on the per capita consumption of the antagonistic larvae. In the first year, the most destructive group were the dolichopodid flies, killing three to seven times more bark beetle larvae than the second ranking Lonchaeidae (Dip.) and the Pteromalidae. In the second year, the pteromalid parasitoids killed 2.5 times more larvae than the dolichopodids. Total bark beetle survival was assessed to decrease from 46 to 18% in the course of the 2 years.     

Behavioural sequence in the attraction of the bark beetle Ips typographus to pheromone sources

ABSTRACT. The functions of the two synergistic pheromone components, (4S)- cis -verbenol (cV) and 2-methyl-3-buten-2-01 (MB), and the role of ipsdienol in the attraction of Ips typographus (L.) (Scolytidae) to pheromone sources were studied in the field. Absolute and relative beetle catches were compared between several traps placed at and nearby a central pheromone source: a pipe trap containing the source, a surrounding sticky trap, a nearby window trap, and four distant window traps. A higher catch in the outer down-wind distant traps indicated an up-wind anemotaxis to the source. Increased MB release, with cV constant, increased the proportion caught in the central pipe trap, indicating MB as a landing stimulus. Release of MB alone gave a very small catch. Ipsdienol could not substitute for cV in the synergism with MB. An increase of cV, with MB constant, increased the number of beetles caught, but not the proportion caught in the pipe trap. The sex ratio was equal in the window traps, but fell to 30% males in both sticky and pipe traps, showing that a large proportion of the males attracted to the source did not land. The proportion of males in the pipe trap was reduced at the highest cV dose. The results support the idea of each pheromone component having a different relative importance in releasing different steps in the behavioural chain.     

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.     

Flight propensity and diapause incidence in five populations of the bark beetle Ips typographus in Scandinavia

Emergence from brood logs, take-off activity and the duration of tethered flight was recorded in the first laboratory generation of the bark beetle Ips typographus L. (Coleoptera: Scolytidae) from five locations (ca 300 km apart) in Sweden and Denmark. Beetles of northerly origin emerged later from brood logs. This pattern was associated with an increasing proportion on non-fliers towards the north. After overwintering, both the rate of development of flight activity and the proportion of non-fliers were the same among populations. Flight duration of fliers was similar among populations and appeared unaffected by outbreak conditions.     

Multiple component system of sugars and polyols in the overwintering spruce bark beetle, Ips typographus

Overwintering adults of the spruce bark beetle, Ips typographus (L.) showed an unusually complex sugar/polyol cryoprotectant system. The major components of the multiple system were: glucose (177.6 mmolL(-1), March); trehalose (175.0 mmolL(-1), December); sorbitol (147.9 mmolL(-1), January); mannitol (81.2 mmolL(-1), March); and erythritol (40.7mmolL(-1), March) (in the parentheses, the maximum concentrations are shown and the month when they were reached). Other minor components were glycerol, fructose, threitol, myo-inositol, arabinitol and ribitol. Distinct seasonal patterns of accumulation/depletion in various components were found. Glycerol, trehalose and glucose started to accumulate first, during early autumn, when the air temperatures fluctuated between 20 and 0 degrees C, and diapause beetles continued in feeding. Glycerol was depleted, glucose remained stable and trehalose continued in accumulation during late autumn when the temperatures oscillated around 0 degrees C. During early winter severe frosts reaching -20 degrees C came, the beetles terminated their diapause and trehalose was partially depleted, while mannitol, sorbitol, fructose, threitol and erythritol started to accumulate. Cold weather continued also during late winter when the beetles remained quiescent. During this period, trehalose was re-accumulated, threitol and erythritol continued to increase, mannitol remained stable and sorbitol, fructose decreased. All cryoprotectans were finally cleared in the beetles which were spontaneously leaving bark during early spring. The seasonal maximum of total concentration of all cryoprotectants (578.2 mOsmol L(-1)) was reached in March. Such a concentration results in colligative depression of melting point of body fluids down by 1.08 degrees C only. It suggests that the potential cryoprotective effect of accumulated sugars and polyols was related rather to their non-colligative functions.     

Characteristics of Norway spruce trees (Picea abies) surviving a spruce bark beetle (Ips typographus L.) outbreak

The characteristics of spruce individuals, which survived a massive bark beetle outbreak, were compared with the characteristics of neighbouring attacked trees in Šumava National Park (Czech Republic). Selected parameters related to crown geometry, stand conditions and distances between trees were measured or estimated. Significant differences were found between the surviving trees and the neighbouring trees attacked by I. typographus. Trees with a higher level of stem shading (longer crown length) tended to survive. The attacked trees were usually located in areas with larger basal area, especially southwards from them. A shorter distance to a previously attacked tree increased the probability of additional attack. Spruce trees with more progressive crown structure transformation (primary structure defoliation) were significantly more frequently attacked by spruce bark beetle. Superior and taller trees had a clearly longer life expectancy than dominant ones. These results show that the attack of trees by bark beetle can be predicted to a certain degree, which can be used in management of endangered spruce forests.     

Significance of parasitoids in the reduction of oak bark beetle Scolytus intricatus Ratzeburg (Col., Scolytidae) in Serbia

Abstract:  As the vector of vascular fungi of the genus Ophiostoma the oak bark beetle, Scolytus intricatus , is one of the significant links in the chain of agents of oak forest decline in Serbia. It is known that the adults of this bark beetle, which develop under the bark of the trees infected by fungi of the genus Ophiostoma , transport the spores of these fungi. During the maturation feeding, the spores are transmitted to healthy tree crowns, where they germinate and cause infection. In period 1992–96 at 27 localities in Serbia, the significance of parasitoids in the reduction of this bark beetle was examined, as the intensity of spore transmission depends upon the number of oak bark beetle adults in nature. In the research of parasitoids of S. intricatus 20 species were identified in five families of Hymenoptera: Braconidae (six species), Eurytomidae (one), Pteromalidae (10), Eupelmidae (one) and Eulophidae (two). Among these parasitoids the greatest influence on the abundance of oak bark beetle was the species Ecphylus silesiacus . It was identified in 90.91% of study samples, its domination was 39.15% and the percentage of oak bark beetle parasitism was 5.66%. In addition, the species Entendon ergias , Dendrosoter protuberans and Cheiropachus quadrum were significant in reduction of S. intricatus . The average percentage of parasitism of oak bark beetle by E. ergias was 2.74%, by D. protuberans it was 2.63% and by Ch. quadrum 1.63%. The significance of other parasitoids in the reduction of oak bark beetles was low. In the study period the total parasitism of oak bark beetle varied between a minimum of 8.64% in 1992 and a maximum of 19.64% in 1996. The average for the whole study period was 14.49%.     

The role of beetle and host volatiles in host colonization in the European oak bark beetle, Scolytus intricatus (Ratzeburg) (Col., Scolytidae)

Abstract:  To understand the role of chemical signals involved in Scolytus intricatus (Ratzeburg) (Col., Scolytidae) host colonization, the attractiveness of intact and beetle colonized host material was investigated in the field and in the laboratory. In the field, chemical signals operating at long range were investigated by means of sticky traps. In the laboratory, close-range chemical interactions were investigated with an arena olfactometer. Field experiments showed no differences in the attractiveness between infested and non-infested host material. On the contrary, laboratory experiments revealed higher attractiveness of infested host and beetle-produced frass in comparison with intact host and mechanically produced sawdust respectively. Laboratory data also disclosed the attractiveness of beetle extracts of both sexes. Our data show that: (1) host kairomones play an important role during host colonization, and that (2) S. intricatus does not use a sex-specific secondary attractant system. Differences between results of field and laboratory trials are discussed.     

An attack of Ips amitinus (Coleoptera: Curculionidae: Scolytinae) on arboretum in West Siberia: New host of invasive bark beetle among exotic conifers

Invasive populations of small spruce bark beetle Ips amitinus were first registered in 2019 in the southeast of Western Siberia. In natural stands of Siberian pine (Pinus sibirica Du Tour), several hundred hectares of outbreak foci of the alien bark beetle were identified. In 2020, a local focus of the bark beetle was found in the conifer collection in the arboretum “Kedr” of the Institute of Monitoring Climatic and Ecological Systems SB RAS, 30 km from Tomsk. The bark beetle caused the main damage to the collection of pines. I. amitinus colonized both host plants Scotch pine (Pinus sylvestris L.) and mountain pine (Pinus mugo Turra), which were previously known to it in the native range in Europe, and the local Siberian species Siberian pine (Pinus sibirica Du Tour), Siberian spruce (Picea obovata Ledeb.) and introduced Far Eastern Korean pine (Pinus koraiensis Sieb. et Zucc.). Demographic characteristics of I. amitinus studied on damaged trees indicate its high reproduction potential in Siberia. The bark beetle outbreak focus was suppressed; however, this plantation requires further annual monitoring of pest abundance and distribution, both to preserve the scientific dendroecological field station and to study the implementation of sential plant conception in relation to the invasion of I. amitinus.     

Nutrient-mediated germination of Beauveria bassiana conidia on the integument of the bark beetle Dendroctonus ponderosae (Coleoptera:Scolytidae)

Field-collected adult mountain pine beetles, Dendroctonus ponderosae, were inoculated with the white muscardine fungus, Beauveria bassiana, and thoroughly examined externally with a scanning electron microscope. Germinating conidia were found at a very low incidence, and only on antennal clubs. However, mortality of inoculated controls was high, and B. bassiana was confirmed as the causative agent. Germination on the cuticle was greatly increased by sonication of adult beetles. The hypothesis that hemolymph released through sonication-damaged membranes provided a nutrient stimulus that enhanced conidial germination was tested by placing hemolymph or yeast-malt extract broth on the cuticle of otherwise nontreated beetles, which were then inoculated with conidia. Significant germination occurred on the cuticle of these beetles. Therefore, a limiting factor for conidial germination on the sclerotized cuticle of D. ponderosae is probably a lack of sufficient nutrients.     

Physiological and biochemical analysis of overwintering and cold tolerance in two Central European populations of the spruce bark beetle, Ips typographus

Overwintering success is one of the key aspects affecting the development and outbreaks of the spruce bark beetle, Ips typographus (L.) populations. This paper brings detailed analysis of cold tolerance, and its influence on overwintering success, in two Central European populations of I. typographus during two cold seasons. Evidence for a supercooling strategy in overwintering adults is provided. The lower lethal temperature corresponds well to the supercooling point that ranges between −20 and −22 °C during winter months. The supercooled state is stabilized by the absence of internal ice nucleators and by seasonal accumulation of a mixture of sugars and polyols up to the sum concentration of 900 mM. The cryoprotective function of accumulated metabolites is probably based on increasing the osmolality and viscosity of supercooled body fluids and decreasing the relative proportion of water molecules available for lethal formation of ice nuclei. No activity of thermal hysteresis factors (stabilizers of supercooled state) was detected in hemolymph. Lethal times for 50% mortality (Lts50) in the supercooled state at −5, −10 or −15 °C are weeks (autumn, spring) or even months (winter), suggesting relatively little mortality caused by chill injury. Lts50 at −15 °C are significantly shorter in moist (6.9 days) than in dry (>42 days) microenvironment because there is higher probability of external ice nucleation and occurrence of lethal freezing in the moist situation.