Inducibility of chemical defenses in Norway spruce bark is correlated with unsuccessful mass attacks by the spruce bark beetle

Secondary attraction to aggregation pheromones plays a central role in the host colonization behavior of the European spruce bark beetle Ips typographus. However, it is largely unknown how the beetles pioneering an attack locate suitable host trees, and eventually accept or reject them. To find possible biomarkers for host choice by I. typographus, we analyzed the chemistry of 58 Norway spruce (Picea abies) trees that were subsequently either (1) successfully attacked and killed, (2) unsuccessfully attacked, or (3) left unattacked. The trees were sampled before the main beetle flight in a natural Norway spruce-dominated forest. No pheromones were used to attract beetles to the experimental trees. To test the trees' defense potential, each tree was treated in a local area with the defense hormone methyl jasmonate (MeJ), and treated and untreated bark were analyzed for 66 different compounds, including terpenes, phenolics and alkaloids. The chemistry of MeJ-treated bark correlated strongly with the success of I. typographus attack, revealing major chemical differences between killed trees and unsuccessfully attacked trees. Surviving trees produced significantly higher amounts of most of the 39 analyzed mono-, sesqui-, and diterpenes and of 4 of 20 phenolics. Alkaloids showed no clear pattern. Differences in untreated bark were less pronounced, where only 1,8-cineole and (-)-limonene were significantly higher in unsuccessfully attacked trees. Our results show that the potential of individual P. abies trees for inducing defense compounds upon I. typographus attack may partly determine tree resistance to this bark beetle by inhibiting its mass attack.     

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.     

Evidence for low-titre infections in insect symbiosis: Wolbachia in the bark beetle Pityogenes chalcographus (Coleoptera, Scolytinae)

Wolbachia are obligatory endosymbiotic α-proteobacteria found in many insect species. They are maternally transmitted and often exhibit reproductive phenotypes like cytoplasmic incompatibility. Pityogenes chalcographus is a bark beetle causing severe damage in spruce stands. Its European populations are divided into several mitochondrial clades separated by partial crossing barriers. In this study, we tested a large sample set covering the natural range of the beetle in Europe for the presence of Wolbachia and associations between infection pattern and mitotypes using a highly sensitive nested PCR technique. 35.5% of the individuals were infected with the endosymbiont and two distinct strains were identified. Both strains occur in low titre not accessible by conventional detection methods. The infections are present all over Europe, unlikely to cause the partial crossing barriers in this host and uncoupled from mitochondrial clades. This pattern is indicative for populations evolving towards endosymbiont loss and for repeated intraspecific horizontal transfer of Wolbachia . Alternatively, the low-titre infections found in P. chalcographus are yet another example for Wolbachia that can persist in host species at low densities and frequencies.     

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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The role of sulphur compounds for breeding success of Ips typographus L. (Col., Scolytidae) on Norway Spruce (Picea abies [L.] Karst.)

Bark beetles, especially Ips typographus L. represent a severe biotic threat for spruce ( Picea abies [L.] Karst.) at low altitudes in Europe. We compared sulphur (total S, SO₄²⁻, glutathione, cysteine, methionine), nitrogen (total N, NO₃⁻, total protein, free amino acids), carbon, total phosphorus and PO₄³⁻, tree vigour index (TVI) and water content of the phloem after felling, and their dependent changes (tdc) with the breeding success of I. typographus . Twenty trees were classified according to age (34/90 years) and crown density (high/intermediate/low). Water content was higher in young trees than in old trees, higher in the crown than at breast height, and decreased significantly within the 8-week study period. In old trees, breeding success, length of mother galleries and SO₄²⁻ were significantly higher, while total protein, NO₃⁻ and water content were significantly lower than in young trees. Trees with intermediate crown density provided the best breeding success for I. typographus and had significantly higher arginine content and C/N ratio as well as low amounts of phosphate and glutamine. During the period of bark beetle breeding, total sulphur, glutathione, protein, NO₃⁻, aspartate, glutamine, glutamate, arginine and γ-aminobutyrate decreased significantly. The results support previous investigations that I. typographus develops best in physiologically weakened trees.     

The Red-belted Bracket (Fomitopsis pinicola) colonizes spruce trees early after bark beetle attack and persists

The Red-belted Bracket (Fomitopsis pinicola) is one of the major decomposers of coniferous wood in Europe and can reach high densities after outbreaks of bark beetles. However, factors of dead wood type and decay stage, which determine the growth of reproductive biomass, i.e. basidiomes, remain unclear. In 2013, we surveyed 1280 dead wood objects and vital trees in spruce stands killed by the bark beetle Ips typographus in 2012, 2002, 1992 and in undisturbed stands for the presence, number, mean basidiome size and total volume of basidiomes. Living basidiomes were equally abundant on dead wood 1, 11, and 21 y after bark beetle outbreak, but were lacking on living trees. Our results indicate that F. pinicola is an effective early colonizer of the huge resource pulse of dead wood caused by the outbreak of bark beetles and basidiomes can persist for 21 y.     

Wildfire provides refuge from local extinction but is an unlikely driver of outbreaks by mountain pine beetle

Bark beetle outbreaks and wildfire are important disturbances in conifer ecosystems, yet their interactions are not well understood. We evaluated whether fire injury increased susceptibility of lodgepole pines (Pinus contorta) to mountain pine beetle (Dendroctonus ponderosae Hopkins), how it influenced beetle reproductive success, and whether beetle population phase altered this interaction. Eight sites that experienced wildfire and eight unburned sites were examined in the Greater Yellowstone Ecosystem (USA). Half were in areas where D. ponderosae was undergoing outbreaks, and half were in areas with low populations. We examined 2056 trees one year after fire for burn injury and beetle attack. We quantified beetle reproductive success in a random sample of 106 trees, and measured gallery areas of D. ponderosae and competing subcortical herbivores in 79 additional trees. Baited flight traps sampled stand-level populations of subcortical herbivores and predators. Wildfire predisposed trees to D. ponderosae attack, but nonlinearly, with moderately injured trees being most preferred. This tree-level interaction was influenced by stand-level beetle population size, in that both healthy and fire-injured trees of all classes were attacked where populations were high, but no healthy trees, and only low and moderately injured trees were killed where populations were low. The number of adult brood produced per female was likewise curvilinear, being highest in moderately injured trees. This reflected an apparent trade-off, with high intraspecific competition arising from the large number of beetles needed to overcome defenses in healthy trees, vs. high interspecific competition and low substrate quality in more injured trees. These results suggest that fire-injured trees can provide a reservoir for D. ponderosae during periods when populations are too low to overcome defenses of healthy trees, and might otherwise face localized extinction. However, the likelihood of populations increasing from endemic to outbreak levels in response to increased susceptibility is offset by the opposing constraints of lower substrate quality and higher competitor load in severely injured hosts, and the relative scarcity of moderately injured trees. Wildfire may confer some reproductive increases to populations already outbreaking. We present a conceptual model of how these disturbances and inherent feedbacks interact to affect beetle population dynamics.     

Attack dynamics of the pine shoot beetle, Tomicus piniperda (Col.; Scolytinae) in Scots pine stands defoliated by Bupalus piniaria (Lep.; Geometridae)

Abstract 1 After a 1‐year, extensive pine looper (Bupalus piniaria) outbreak, plots were laid out to study tree susceptibility to attack, and performance of Tomicus piniperda in pine trees suffering from varying levels of defoliation. 2 Tomicus piniperda was the dominating stem‐attacking species among the primary stem colonizers, and 82% of all trees that died had been colonized by T. piniperda. 3 Beetle attacks primarily struck severely defoliated trees, i.e. trees that suffered from 90% to 100% defoliation. 4 Beetle attacks peaked in the second year after cessation of the outbreak, and suppressed trees were both more frequently attacked and more susceptible to beetle attack than intermediate and dominant trees. 5 Trees surviving beetle attacks carried more foliage than trees that did not survive the attacks. 6 A single year of severe defoliation is enough to render pine trees susceptible to secondary pests, such as T. piniperda.     

Successful colonization, reproduction, and new generation emergence in live interior hybrid spruce Picea engelmannii×glauca by mountain pine beetle Dendroctonus ponderosae

1 Although mountain pine beetle Dendroctonus ponderosae Hopkins are able to utilize most available Pinus spp. as hosts, successful colonization and reproduction in other hosts within the Pinaceae is rare.
2 We observed successful reproduction of mountain pine beetle and emergence of new generation adults from interior hybrid spruce Picea engelmannii × glauca and compared a number of parameters related to colonization and reproductive success in spruce with nearby lodgepole pine Pinus contorta infested by mountain pine beetle.
3 The results obtained indicate that reduced competition in spruce allowed mountain pine beetle parents that survived the colonization process to produce more offspring per pair than in more heavily-infested nearby pine.
4 We also conducted an experiment in which 20 spruce and 20 lodgepole pines were baited with the aggregation pheromone of mountain pine beetle. Nineteen pines (95%) and eight spruce (40%) were attacked by mountain pine beetle, with eight (40%) and three (15%) mass-attacked, respectively.
5 Successful attacks on nonhost trees during extreme epidemics may be one mechanism by which host shifts and subsequent speciation events have occurred in Dendroctonus spp. bark beetles.     

Potential impact of global warming on deciduous oak dieback caused by ambrosia fungus Raffaelea sp. carried by ambrosia beetle Platypus quercivorus (Coleoptera: Platypodidae) in Japan

Deciduous oak dieback in Japan has been known since the 1930s, but in the last ten years epidemics have intensified and spread to the island's western coastal areas. The symbiotic ambrosia fungus Raffaelea sp. is the causal agent of oak dieback, and is vectored by Platypus quercivorus (Murayama). This is the first example of an ambrosia beetle fungus that kills vigorous trees. Mortality of Quercus crispula was approximately 40% but much lower for associated species of Fagaceae, even though each species had a similar number of beetle attacks. It is likely that other oaks resistant to the fungus evolved under a stable relationship between the tree, fungus and beetle during a long evolutionary process. Quercus crispula was probably not part of this coevolution. This hypothesis was supported by the fact that P. quercivorus showed the least preference for Q. crispula yet exhibited highest reproductive success in this species. Therefore, P. quercivorus could spread more rapidly in stands with a high composition of Q. crispula. The present oak dieback epidemic in Japan probably resulted from the warmer climate that occurred from the late 1980s which made possible the fateful encounter of P. quercivorus with Q. cripsula by allowing the beetle to extend its distribution to more northerly latitudes and higher altitudes. Future global warming will possibly accelerate the overlapping of the distributions of P. quercivorus and Q. crispula with the result that oak dieback in Q. crispula will become more prevalent in Japan.     

Sequential patterns of colonization of coarse woody debris by Ips pini (Say) (Coleoptera: Scolytidae) following a major ice storm in Ontario

Abstract

• 1 It is widely known that many bark and wood‐boring beetle species use nonresistant coarse woody debris (CWD) created by disturbances; however, the ability of these secondary species to cause mortality in healthy trees following a build‐up of their populations remains unclear. We characterized the pattern of colonization by Ips pini (Say) following a major ice storm that created large amounts of CWD varying in resistance to colonization (i.e. ranging from snapped tops with no resistance to heavily damaged trees with intact root systems). A major question was how the beetles responded to the different types of storm‐damaged material and whether healthy undamaged trees were colonized and killed following increases in beetle populations.
• 2 Six red pine, Pinus resinosa Ait., plantations in eastern Ontario were monitored from 1998 to 2001 inclusive: three with high storm damage (approximately 120 m³/ha CWD) and three with minimal damage (approximately 20 m³/ha CWD). Transects (200 × 2 m) were sampled yearly in each plantation to assess the type and amount of damaged pine brood material colonized by the pine engraver beetle, I. pini.
• 3 Beetles preferentially infested the most nonresistant material available each year (i.e. all snapped tops in year 1, all standing snags, up‐rooted trees and many bent trees by year 2, but still less than 50% of trees blown over but with intact root systems by year 3). By years 3 and 4, the majority (approximately 75%) of severely damaged trees (with > 50% crown loss) died prior to beetle colonization.
• 4 The size of the beetle population tracked the abundance of available woody material from year‐to‐year within a plantation; populations were very large in the first 2 years, and declined significantly in the last 2 years.
• 5 Healthy standing red pines were apparently resistant to colonization by the beetles, despite the significant build‐up in their populations. Hence, the results of the present study suggest that native bark beetle populations will not cause further tree mortality following such a disturbance in this region.

     

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.     

Phylogeography of a host-specific insect: genetic structure of Ips typographus in Europe does not reflect past fragmentation of its host

The phylogeography of the bark beetle Ips typographus was assessed using five microsatellite markers. Twenty-eight populations were sampled throughout Europe on the host tree Picea abies . I. typographus showed very low levels of genetic diversity, and the study revealed a lack of genetic structure across Europe. No significant barrier to gene flow was found, even though P. abies has a fragmented distribution. A weak but significant effect of isolation by distance was found. These results suggest a high dispersal capacity of I. typographus , which leads to low genetic differentiation between populations. Its high dispersal capacity is likely to have prevented I. typographus from developing important local adaptations to its host, which would have influenced its genetic structure. The nuclear data was compared to previously published mitochondrial data that showed strong differentiation between Central–Northern European populations and Russian–Baltic populations, and a founder effect in Scandinavia, probably reflecting the postglacial history of I. typographus . Discrepancies between nuclear and mitochondrial markers could be due to the maternal inheritance of mitochondrial DNA, and to sex-biased dispersal in I. typographus . The overall low genetic diversity observed on both markers on a large geographical scale is discussed. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 239–246.     

The plot thickens: does low density affect visitation and reproductive success in a perennial herb, and are these effects altered in the presence of a co-flowering species?

Plants may experience reduced reproductive success at low densities, due to lower numbers of pollinator visits or reduced visit quality. Co-occurring plant species that share pollinators have the potential to facilitate pollination by either increasing numbers of pollinator visits or increasing the quality of visits, but also have the potential to reduce plant reproductive success through competition for pollination. I used a field experiment with a common distylous perennial (Piriqueta caroliniana) in the presence and absence of a co-flowering species (Coreopsis leavenworthii) in plots with one of four different distances between conspecific plants. I found strong negative effects of increasing interplant distance (related to conspecific density) on several components of P. caroliniana reproductive success: pollinator visits to plants per plot visit, visits received by individual plants, conspecific pollen grains on stigmas, outcross pollen grains on stigmas, and probability of fruit production. Although P. caroliniana and C. leavenworthii share pollinators, the co-flowering species did not affect visitation, pollen receipt or reproductive effort in P. caroliniana. Pollinators moved very infrequently between species in this experiment, so floral constancy might explain the lack of effect of the co-flowering species on P. caroliniana reproductive success at low densities. In co-occurring self-incompatible plants with floral rewards, reproductive success at low density may depend more on conspecific densities than on the presence of other species.     

云南切梢小蠹对云南松树的蛀干危害及致死机理

蛀干危害是云南切梢小蠹致死云南松树的关键环节。通过控制云南切梢小蠹蛀干密度,对云南切梢小蠹在自然条件下蛀干行为与危害进行了首次探讨。结果表明,云南切梢小蠹蛀干密度与云南松存活率呈负相关,蛀干密度直接决定云南松死亡或存活。研究发现,蛀干密度115坑/m2是云南松树的最低致死密度阈值,云南松树在蛀干密度低于26.4坑/m2情况下存活,在26.4-115坑/m2有部分存活,超过115坑/m2以后将被害致死。云南切梢小蠹对树干攻击形成有卵和无卵两类坑道。形成无卵坑道的蛀干攻击可导致树势衰弱,形成有卵坑道的蛀干危害严重破坏了韧皮组织,是导致云南松死亡的直接原因。     

A New Outbreak of the European Spruce Bark Beetle,Ips typographus (L.) (Coleoptera,Curculionidae) in Leningrad Province

Entomological Review - A new and potentially severe outbreak of the European spruce bark beetle Ips typographus began in Leningrad Province in 2021. The permanent presence of the species in...     

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.     

Effects of density on the reproductive success of pine engravers: is aggregation in dead trees beneficial?

1. The pine engraver bark beetle Ips pini (Say) (Coleoptera: Scolytidae), aggregates primarily on dead or dying pine trees. In this study pine engravers were laboratory-reared on logs at a range of low densities to determine whether there was a fecundity advantage of breeding aggregations.
2. Mean reproductive success for both males and females declined exponentially with increasing density.
3. Female pine engravers had shorter egg galleries at higher densities, suggesting that they left high-density breeding sites earlier. This would reduce the number of eggs that failed to survive due to larval competition.
4. Some pine engravers colonized the logs voluntarily during the experiment. These volunteers settled independently of the original density.
5. The fungus Ophiostoma sp. was present on the logs and may be competing with the pine engravers for limited bark area.
6. Aggregation resulted in a considerable cost to pine engraver reproductive success even at low densities. Thus, it remains perplexing why pine engravers aggregate actively in nature.     

Attacks on living spruce trees by the bark beetle Ips typographus (Col. Scolytidae) following a storm-felling: a comparison between stands with and without removal of wind-felled trees

Abstract 1 To maintain biodiversity in forests more wind‐felled trees must be left where they fall. 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 In the 5 years following a major storm disturbance the number of standing spruces killed by I. typographus was determined in a total of 53 stands. In five of the stands all wind‐thrown trees were left (unmanaged stands) and in 48 of the stands, which were situated at distances of 1.4–10.0 km from each focal unmanaged stand, the wind‐felled trees were removed directly after the storm (managed stands). In the winter preceding the fifth summer new storm‐fellings occurred in the study area. 3 In the 4‐year period between the first and second storm‐fellings, 50–322 standing trees were killed by I. typographus per unmanaged stand. There was a direct linear relationship between the number of storm‐felled spruces colonized by I. typographus and the number of trees subsequently killed in the unmanaged stands. 4 Tree mortality caused by I. typographus in the unmanaged stands was almost nil in the first year, peaked in the second or third year, and decreased markedly to a low level in the fourth and fifth years. 5 In the 4‐year period between the first and second storm‐fellings twice as many trees were killed per ha in the unmanaged stands than in the managed stands: the average difference being 6.2 killed trees per ha, equivalent to 19% of the number of spruce trees felled by the first storm in the unmanaged stands. 6 Much higher numbers of trees were killed per ha in the stand edges than in the interiors of both the unmanaged and the managed stands.     

Early responses of bark and wood boring beetles to an outbreak of the hemlock looper Lambdina fiscellaria (Guenée) (Lepidoptera: Geometridae) in a boreal balsam fir forest of North America

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