Density-mediated responses of bark beetles to host allelochemicals: a link between individual behaviour and population dynamics

Abstract  1. Bark beetles (Coleoptera: Scolytidae) accept or reject host conifers based partly on concentrations of phloem monoterpenes. They colonise trees in aggregations, in response to pheromones that attract flying beetles to trees undergoing colonisation. A series of entry and gallery construction assays was conducted to determine whether responses by individual beetles to monoterpenes are altered by pheromones and/or the presence of other beetles.
2. Entry into the amended media by Ips pini and the length of time until entry were not influenced by the presence of aggregation pheromones.
3. Entry into amended media was influenced by the presence of other beetles on the surface of, or constructing galleries in, the substrate. The effects of alpha-pinene and limonene on host entry behaviour were mediated by the density of beetles on the surface of the assay arena, and by the density of beetles constructing galleries within the medium.
4. The percentage of beetles entering medium amended with higher concentrations of monoterpenes increased with increased density of beetles on the surface of the assay arena, until a threshold density of three or four beetles per assay arena, after which entrance rate declined.
5. The presence of other beetles constructing galleries elicited more rapid entry by the test beetles.
6. Gallery lengths were generally higher in the presence of aggregation pheromones.
7. Gallery lengths increased with increased density of beetles within the assay arena.
8. These results suggest a link between the density of bark beetles and responses of individuals. This linkage may partially explain behavioural changes observed during population eruptions.     

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.     

我国首次截获检疫性有害生物美东最小齿小蠹

2022年2月1日起,美国、加拿大等国家的松木进口,只能通过我国江苏(南京、连云港)、福建(福州港)等17个指定口岸进境。美国、加拿大进境松木携带疫情复杂,将给指定口岸带来巨大的疫情防控压力。2022年1月,连云港海关在进口美国原木中截获了美东最小齿小蠹。该小蠹在我国无分布,为国内首次截获。其形态特征与近似种主要区别为:该齿小蠹体型相对较小,一般为2.1～2.8 mm,侧缘4齿各自独立,其中第2齿和第3齿着生在共同的基部。通过初步风险分析,其通过指定口岸入侵我国的可能性很大,一旦成功入侵定殖,将对我国的林业资源造成严重威胁,各相关指定口岸应加强对北美进境原木的检疫。     

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.     

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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Distribution of Norway spruce bark and wood‐boring beetles along Alpine elevational gradients

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Budding: A new stage in the development of Chytridiopsis typographi (Zygomycetes: Microsporidia)

Chytridiopsis typographiWeiser, 1954, the microsporidian pathogen of the spruce bark beetle, Ips typographus L. (Coleoptera: Scolytidae), has an early developmental period with plurinucleate mother cells, each of which produces a single bud. The globular bud is connected with the mother cell by a collar and the cellular constituents are pushed to the distant end of the bud. Both the mother cell and the bud continue to develop; the bud then separates from the mother cell and grows to produce a cell of the same type. Both cells then continue sporogonial development and produce sporophorous vesicles with 16-32 spores. The process of a single mother cell producing a single bud that grows to an identical stage is new in the development of C. typographi and has no analogy in other Microsporidia.     

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.

     

Pine monoterpenes and pine bark beetles: a marriage of convenience for defense and chemical communication

Pine-feeding bark beetles (Coleoptera: Scolytidae) interact chemically with their host pines (Coniferales: Pinaceae) via the behavioral, physiological, and biochemical effects of one class of isoprenoids, the monoterpenes and their derivatives. Pine monoterpenes occur in the oleoresin and function as behaviorally active kairomones for pine bark beetles and their predators, presenting a classic example of tri-trophic chemical communication. The monoterpenes are also essential co-attractants for pine bark beetle aggregation pheromones. Ironically, pine monoterpenes are also toxic physiologically to bark beetles at high vapor concentrations and are considered an important component of the defense of pines. Research over the last 30 years has demonstrated that some bark beetle aggregation pheromones arise through oxygenation of monoterpenes, linking pheromone biosynthesis to the host pines. Over the last 10 years, however, several frequently occurring oxygenated monoterpene pheromone components (e.g., ipsenol, ipsdienol and frontalin) have also been shown to arise through highly regulated de novo pathways in the beetles (reviewed in Seybold and Tittiger, 2003). The most interesting nexus between these insects and their plant hosts involves the late-stage reactions in the monoterpenoid biosynthetic pathway, during which isomeric dimethylallyl diphosphate and isopentenyl diphosphate are ultimately elaborated to stereospecific monoterpenes in the trees and to hydroxylated monoterpenes or bicyclic acetals in the insects. There is signal stereospecificity in both production of and response to the monoterpenoid aggregation pheromones of bark beetles and in response to␣the monoterpenes of the pines. In the California fivespined ips, Ips paraconfusus, we have discovered a number of cytochome P450 genes that have expression patterns indicating that they may be involved in detoxifying monoterpene secondary metabolites and/or biosynthesizing pheromone components. Both processes result in the production of oxygenated monoterpenes, likely with varying degrees of stereospecificity. A behavioral analysis of the stereospecific response of I. paraconfusus to its pheromone is providing new insights into the development of an efficacious bait for the detection of this polyphagous insect in areas outside the western United States. In contrast, a Eurasian species that has arrived in California, the Mediterranean pine engraver, Orthotomicus (Ips) erosus, utilizes both a monoterpenoid (ipsdienol) and a hemiterpenoid (2-methyl-3-buten-2-ol) in its pheromone blend. The stereospecificity of the response of O. erosus to the monoterpenoid appears to be the key factor to the improved potency of the attractant bait for this invasive species.Dedicated to Professor David L. Wood on the occasion of his 75th birthday, January 8, 2006     

A simple method for the detection of imaginal diapause in beetles

Abstract:  Investigations on Ips typographus and Leptinotarsa decemlineata revealed that the activity of mitochondrial enzymes in the flight muscles provides a reliable criterion for the discrimination of diapausing and non-diapausing adults. Enzyme activity is conveniently detected in situ with commercially available tetrazolium salts. Staining intensity is correlated with the flight ability and often also with reproduction.