Biosynthesis of 2-methyl-3-buten-2-ol,a pheromone component of Ips typographus (Coleoptera: Scolytidae)

Exposure of beetles to ¹⁴C-labelled mevalonate by injection, resulted in significant incorporation of radioactivity in 2-methyl-3-buten-2-ol. Radiolabelled 2-methyl-3-buten-2-ol was obtained both by organic solvent extraction of beetle hindguts and by entrainment of volatiles in air surrounding logs with boring beetles. It is suggested that 2-methyl-3-buten-2-ol, an essential component of the aggregation pheromone of Ips typographus, can be synthesized from mevalonate.     

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.     

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.     

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.     

Interruption of aggregation pheromone in Ips typographus (L.) (Col. Scolytidae) by non-host bark volatiles

Abstract 1 The antennally active nonhost bark volatiles (NHVs): trans‐conophthorin (tC), C₆‐alcohols (green leaf volatiles; GLVs) and C₈‐alcohols, were tested for their ability to reduce attraction of the spruce bark beetle Ips typographus (L) (Col. Scolytidae) to its pheromone sources in both laboratory walking bioassy and field trapping experiments. 2 In the walking bioassay with I. typographus females, individual NHVs such as tC, 3‐octanol and 1‐octen‐3‐ol, and the unsuitable host signal, verbenone (Vn), were inactive at the doses tested. However, the blend of C₆‐alcohols (3GLVs) and all the binary, ternary, or quarternary blends significantly reduced the female attraction to the pheromone sources. 3 In the field trapping experiments, individual NHV signals (tC, C6‐alcohols and C₈‐alcohols) all reduced catch of I. typographus in pheromone‐baited traps, with their inhibitory effects similar to that of the known inhibitor, Vn. The binary, ternary or quarternary combinations of these NHV signals or Vn, all caused significantly stronger reductions in trap catches than the individual signals. The blends showed similar levels of interruption, except the binary blend of C₈‐alcohols (2C8OH) and Vn. 4 Difference in trapping mechanism between pipe traps (attraction and landing) and Lindgren funnel traps (attraction) did not affect the pattern of inhibition of these active NHV signals and Vn. 5 These behaviourally active nonhost volatiles and Vn might be used effectively to protect spruce trees or stands against attacks by I. typographus.     

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.     

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.     

Biological differences reflect host preference in two parasitoids attacking the bark beetle Ips typographus (Coleoptera: Scolytidae) in Belgium

The basic reproductive biology of two ectoparasitoids developing on the late larval instars of the scolytid Ips typographus Linnaeus, a pest of spruce forests in Eurasia, was studied with the purpose of explaining which biological features allow the two species to share the same host. The anautogenous braconid Coeloides bostrichorum Giraud had a longer pre-oviposition period (5.1 vs. 3.3 days), a greater egg load (8.1 vs. 6.1 eggs), survived longer and emerged later than the pteromalid Rhopalicus tutela (Walker). In contrast, R. tutela was autogenous and tended to be more fecund under constrained conditions (9.7 vs. 5.1 total offspring per female). The longer pre-oviposition period of the specialist C. bostrichorum, coupled with its greater longevity, afforded the opportunity of better synchronization of ovipositing females with late instar larvae of I. typographus. By contrast, the polyphagous R. tutela matured rapidly, allowing parasitism of both younger and older larval instars of I. typographus in addition to other species. These small differences favoured the co-occurrence of the two parasitoid species on the same attacked trees.     

Tree killing by Ips typographus (Coleoptera: Scolytidae) at stand edges with and without colonized felled spruce trees

Abstract 1 To maintain biodiversity in managed spruce forests in Sweden more wind‐felled trees must be retained. However, there is concern among forest owners that this may result in higher tree mortality caused by the spruce bark beetle, Ips typographus (L.) (Col. Scolytidae). 2 To simulate wind‐felled trees, living spruce trees were cut at spruce stand edges bordering fresh clear‐cuttings. Treatments comprised edges with zero, one or five cut trees colonized by I. typographus. Edges with naturally wind‐felled trees colonized by I. typographus were also included in the analyses. 3 During the two following summers, the number of trees killed by I. typographus did not differ between edges with and without felled trees, or between edges with one or five felled trees. 4 Within edges with felled trees, there were more killed trees close to the felled trees than at other parts of the edges. Thus, felled trees provided focal points for attacks within edges. 5 It is concluded that small numbers of wind‐felled trees colonized by I. typographus may be left near spruce stand edges without increasing the risk of beetle‐induced tree mortality.     

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.     

Influence of proportion of (4S)-cis-verbenol in pheromone bait on Ips typographus (Col., Scolytidae) catch in pheromone trap barrier and in single traps

Abstract:   The possibilities of increasing catching efficiency of male Ips typographus L in pheromone traps barriers and in single traps were tested. Pheromone dispensers with different percentages of (4S)- cis -verbenol (cV) in pheromone mixtures were used. The results show that the different male catching efficiencies of pheromone trap barriers and single traps were related to the different percentages of cV in the pheromone bait. The proportions of males were higher in pheromone trap barriers than in single traps. Thus increasing the catch of males in pheromone trap barriers is possible by using a combination of pheromone traps containing pheromones giving a higher release of cV with others containing pheromones giving a lower release of cV .     

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.     

Can Ips typographus (L.) (Col., Scolytidae) smell the carrion odours of the dead beetles in pheromone traps? Electrophysiological analysis

Abstract:   Head-space samples of Ips typographus dead beetles taken from pheromone traps were tested by combined gas chromatography and electroantennographic detection (GC–EAD) on the antennae of the same species, and identified by GC-mass spectroscopy (MS). The GC-EAD analysis showed that antennae of both sexes responded to 1-hexanol and verbenone from the aeration samples, while the typical and strong carrion odours from the dead beetles such as dimethyl disulphide, 3-methyl-1-butenol (isoamyl alcohol), 2,5-dimethyl pyrazine and isovaleric acid elicited no antennal responses. The EAD active compounds, 1-hexanol and verbenone, have been shown in earlier studies to be inhibitory on attraction of I. typographus to pheromone traps. Thus, the decreased catching efficacy of pheromone traps with many dead beetles might be the result of the release of 1-hexanol and verbenone from the dead beetles, but not to the typical carrion smells which are strongly detected by the human nose.     

Characterization of microsatellite loci in the spruce bark beetle Ips typographus (Coleoptera: Scolytinae)

Ips typographus is an economically important pest of Norway spruce stands. We developed five polymorphic microsatellite markers using a biotin enrichment protocol. The number of alleles ranged from three to 11 per locus and no strong evidence for null alleles was found. Heterozygosity ranged from 0.3 to 0.97. These markers could be useful tools to study the population structure and genetic consequences of I. typographus population outbreaks.     

Occurrence of Ips typographus (Col., Scolytidae) along an urbanization gradient in Brussels, Belgium

Abstract 1 The distribution and dynamics of insect populations in cities is poorly understood. One approach to address this question is to explore the permeability of the urban habitat to species from surrounding rural areas, which can serve as reservoirs in source‐sink dynamics. 2 Here, we present data on the distribution of the forest insect pest of spruce, Ips typographus (Coleoptera, Scolytidae), along two axes entering the city of Brussels (Belgium) from the south‐east and to the town centre. 3 The insect was caught everywhere along these transects, even in heavily urbanized surroundings, and sometimes in relatively high numbers. The catches were highest near the middle of the transects and lower at both ends of them. 4 This pattern was associated, on the one hand, with an urbanization gradient with the numbers of flying individuals increasing with the distance from the city centre and, on the other hand, with lower catches at the periphery of the city where a high proportion of broadleaved trees may have disrupted the response to aggregation pheromones. 5 In addition to the probable rural origin of the beetles, high catches at the Port of Brussels indicated that some of the insects might be of foreign origin and enter the city with imported timber, highlighting a pathway for unintentional introductions of organisms, including potentially invasive species.     

Influence of the proportion of (−) α-pinene in pheromone bait on Ips typographus (Col., Scolytidae) catch in pheromone trap barriers and in single traps

Abstract:  Further possibilities of increasing catch efficiency of Ips typographus L. in pheromone trap barriers with two different levels of release of (4S)- cis -verbenol (cV) and in single traps were tested. Pheromone mixtures containing cV, 2-methyl-3-buten-2-ol (MB) and 0, 1, 10, 35, 60 and 90% (−) α -pinene were prepared. Basically, MB was successively replaced by (−) α -pinene in the mixtures. Tests were performed on the edge of a spruce forest when outbreaks of I. typographus occurred. The substitution of MB with (−) α -pinene had different effects in different types of pheromone trap barriers and in single traps. It is not possible to increase the attractiveness of the bait having a higher percentage of cV by supplementing a certain percentage of MB with (−) α -pinene. The catch of I. typographus decreased with an increase in the percentage of (−) α -pinene in the bait. It is possible to increase the attractiveness of the bait having a lower percentage of cV by supplementing certain percentages of MB with (−) α -pinene. A slight synergistic effect of (−) α -pinene with MB/cV mixture is visible in this type of bait. In the case of single traps, supplementing MB with (−) α -pinene possibly causes a slight synergistic effect. An increase in the percentage of (−) α -pinene increases the percentage of males in the catch.     

Effects of chronic gamma radiation on populations of Ips (Coleoptera: Scolytidae) in trap logs

Abstract. 1. Population dynamics of Ips calligraphus and I. grandicollis (Coleoptera: Scolytidae) were studied in a forest exposed to high doses of gamma radiation.
2. Populations were replicated at eleven dose rates by using 'trap logs'.
3. Adult beetles did not avoid high radiation intensities and attacked all sites equally.
4. Utilization of the cambium-inner bark area varied from c. 2% at a dose rate of 2520 R/20 h day to 90% at dose rates of 63 and 105 R/20 h day.
5. Developmental success of the new brood was directly dependent on the dose rate, and developing progeny were often killed by accumulated exposure.
6. Larger, slower developing species of subcortical beetles were eliminated at dose levels that allowed successful development of the two species of Ips bark beetles.