Generation Of Beetles Research Articles

Emission patterns of volatile organic compounds from Norway spruce logs following bark beetle (Ips typographus L.) infestation.

Norway spruce (Picea abies L.) is economically one of the most important conifer species in Europe. Spruce forests are threatened by outbreaks of the bark beetle Ips typographus L., and this will worsen with a projected warmer and drier climate and increased outbreak dynamic following storms. Volatile terpenes and aromatics play pivotal roles in defence of trees, however, little is known about the emission dynamics of these compounds from trees colonized with I. typographus, particularly in dependence on the beetle's developmental stages and colonisation densities. Here, we analysed the emission profiles of volatile organic compounds (VOCs) from spruce logs colonised with low (LDT) and high (HDT) densities of I. typographus from the initial colonisation until the emergence of the next beetle generation. A first VOCs emission peak appeared directly after colonisation and lasted for one week. It mainly consisted of monoterpenoids and most likely reflected the trees' constitutive defence against herbivory. Under HDT, a second emission maximum occurred during the larval stage, whereas under LDT a second peak appeared later during maturation feeding of callow beetles. In contrast to the first peak, sesquiterpenoids, aromatics and oxygenated monoterpenoids dominated the second peak, possibly reflecting the trees' induced defence. Developing beetles seem to face a variety of defence compounds even if the tree has been overwhelmed and colonisation by parental beetles was already successful. The specific release patterns under LDT and HDT might be due to different availability of precursor compounds, depletion of constitutively stored compounds and differences in microbial activities associated with the bark beetles. The present study highlights constitutive defence of spruce trees upon herbivore attack, and the effect of infestation density on the temporal dynamics of induced defence. Particularly the oxygenated monoterpenoid terpinen-4-ol may be used as cue to assess habitat quality and competition by newly arriving beetles.

The Australian Museum and Friends of Lord Howe survey of large Coleoptera on Lord Howe Island, August 2022

A survey of large beetles, one centimetre or more in length, on Lord Howe Island, was conducted in August 2022 and the results are discussed. In total, 32 large species were found. This was the first survey made at least one beetle generation after eradication of the rodents in 2019, and there was some evidence of recovery, in particular of the large flightless endemic cerambycid, Xylotoles wollastoni (White, 1856), but also of a leaf beetle, Dematochroma picea (Baly, 1864) and an exotic pest of lawns, Heteronychus arator (Fabricius, 1775). There was also evidence of recovery of Carabidae species after the prolonged dry years of 2016 to 2019.

Predator densities alter the influence of non‐consumptive effects on the population dynamics of an agricultural pest

Abstract Augmentative release of predators is used in agriculture to suppress pest populations and minimise crop damage. However, predators affect prey populations not only through consumption but by inducing changes to prey morphology, physiology, behaviour and life history. These risk‐induced trait responses can increase prey fitness, potentially reducing the efficacy of certain predators as biocontrol agents. We investigated how non‐consumptive effects contribute to the overall influence of predators by modelling the effect of the predator Podisus maculiventris on the population dynamics of a major agricultural pest, the Colorado potato beetle (Leptinotarsa decemlineata). We developed a demographic model incorporating both consumption and non‐consumptive Podisus‐induced shifts in beetle reproductive strategy. Our model combines data from multiple mechanistic experiments showing that predator‐exposed beetles produce fewer offspring but increase offspring provisioning, and that provisioned larvae have increased survival when predators are present. We simulated beetle densities across multiple beetle generations and a range of predator densities. The influence of non‐consumptive effects depended on predator density. At low predator densities, non‐consumptive effects strengthened the negative effect of predators by up to 45%, and risk‐induced changes to offspring provisioning had a stronger effect on prey densities than reduced offspring quantity. In contrast, at high predator densities, non‐consumptive effects changed the effect of predators by <5%, likely because beetle densities were very low both with and without non‐consumptive effects. Our results suggest that even adaptive responses to predation risk by prey do not necessarily reduce the ability of predators to suppress pest populations.

Tracking the push towards extinction: combining dispersal and management data to monitor Asian longhorned beetle eradication in the U.S.

Based on the threat posed by the Asian longhorned beetle (Anoplophora glabripennis Motschulsky), many countries including the United States have adopted policies of eradication. The eradication of infestations that cover hundreds of square kilometers can require multiple visual surveys of millions of individual trees. At these scales, eradication may take several decades and span multiple beetle generations. During this period the infestation of new trees adds spatially-explicit risk to the landscape while surveys and the removal of infested trees reduce it. To track dynamic risk on the landscape we have developed the Asian Longhorned Beetle Hazard Management and Monitoring Tool. The geospatial tool combines data documenting; the locations, levels of infestation, and dates of detection of infested trees; the locations, methods, and timing of survey and host removal activities; and a reconstruction of beetle movement within the infested landscape to generate annual spatial estimates of infestation risk based on the combination of beetle dispersal and survey and host removal activities. The analyses of three eradication programs highlight similar patterns in risk through time with risk peaking at the time infestations are detected and declining as management activities slow beetle spread and reduce risk through surveys. However, the results also highlight differences in risk reduction among the eradication programs associated with differences in beetle dispersal among infestations and the size of the infested landscape, highlighting the importance of applying local information to structure eradication programs. The Asian Longhorned Beetle Hazard Management and Monitoring Tool provides a quantitative repeatable approach to tracking changes in infestation risk using local beetle behavior and management efforts. In addition to this, the tool may provide a structure to optimize eradication efforts by allowing managers to estimate expected risk reduction based on proposed survey and host removal strategies.

Fungi associated with the ambrosia beetle Xyleborus perforans (Coleoptera: Curculionidae: Scolytinae) on drought-stressed Pinus in New South Wales, Australia

Ambrosia beetles have co-evolved symbiotic relationships with an array of fungal partners. Mutualistic fungal partners are often highly successful in vertical transmission between beetle generations. These persisting relationships can alter beetle behaviour, resulting in the opportunity to occupy new ecological niches and to spread geographically. In Australia, ambrosia beetles are not currently considered a significant pest in commercial Pinus plantations, where the bark beetle Ips grandicollis is known as the primary invader of stressed trees. However, in 2019, ambrosia beetles Xyleborus perforans and X. bispinatus, co-occurring with I. grandicollis, were found to have colonised a large proportion of drought-stressed trees in commercial Pinus plantations in north-east New South Wales. In this study, X. perforans (the most prevalent of two Xyleborus spp.) was collected from infested dead and dying trees in two NSW Pinus plantations. Fungal isolates of suspected Pinus pathogens were recovered from beetle mycangia and exoskeletons as well as ambrosia beetle galleries. Morphological examination and multilocus sequence analysis identified five fungi associated with X. perforans: Fusarium parceramosum, Fusarium aff. solani, Ophiostoma ips, Raffaelea deltoideospora and Sporothrix pseudoabietina. For Australia, this is the first report of F. parceramosum, as well as the first records of O. ips, R. deltoideospora and S. pseudoabietina being vectored by Xyleborus. Pathogenicity tests were performed on seedlings of three Pinus spp., with O. ips producing significantly longer lesions than the other fungi. This study demonstrates the potential for seemingly harmless ambrosia beetles to vector plant pathogens in Australian forests, providing a mode of disease transmission that should be considered in plantation management and forest biosecurity.

EFFECTIVENESS TESTS OF VEGETABLE INSECTICIDES ESSENTIAL OILS OF MUTMET SEED (Myristica fragrans Houtt.) AND CLOVE FLOWER (Syzygium aromaticum L.) ON RICE BEETLE MORTALITY AND DEVELOPMENT Sitophilus oryzae (Linnaeus, 1763)

This study aims to analyze the inhibition of the development of the F1 generation of rice beetles by nutmeg and clove flower essential oils, and to determine the mortality of rice beetles against nutmeg and clove flower essential oils. The stages of the research started from rearing the rice beetle, preparing test insects, making variations in doses, treatments, and analysis. Two tests were conducted in the study, the first for inhibition of F1 generation activity and the percentage of mortality using the contact method (filter paper). The results showed that nutmeg and clove oil had an effect on the inhibition of the rice beetle F1 generation. Nutmeg oil has the best inhibition power with the percentage of F1 generation inhibition up to 100%. The mortality test using the filter paper method showed that for 48 hours nutmeg essential oil was able to kill rice beetles at all concentrations, namely 5-20% to 100%, while the percentage of 100% mortality was only found in the treatment with clove oil at the highest concentration (20%). The results showed that nutmeg oil showed better results than clove oil for controlling S. oryzae warehouse pests.

The dynamics of wild populations of Henosepilachna vigintioctomaculata Motch. (<i>Coleoptera:Coccinellidae</i>) in Primorsky Krai

Relevance. Population dynamics (population waves) is an intrinsic quality of population systems. These fluctuations can be induced by various factors, e.g. environmental conditions and resource availability, elements of a food chain from the same or a higher level (competitors, parasites, predators), and diseases. Few researchers have addressed the issue of the population dynamics of Henosepilachna vigintioctomaculata in the Russian Far East. This paper investigates the reasons why the potato ladybird beetle became a pest of introduced cultivated plants.Materials and methods. To collect data on imagines, all research sites were examined at intervals of eight days during the entire period of the study. The examination of the research sites was conducted within one day. All the imagines taken from host plants were marked at the first encounter by puncturing their elytra with a sewing needle (0.4 mm in diameter) according to Hirano. The next generation of beetles was marked with nail polish (in two-three days after emergence) to avoid traumatizing the insects. At the second encounter, these beetles were also marked by puncturing their elytra with a needle. The methods implemented did not have an adverse effect on the survivability of the studied imagines. The beetles were released to the same plants where they had been taken from. The research data were analyzed by Jolly’s method.Results. Overwintered imagines appeared in the fields and began ovipositing at the end of May. The first generation of imagines appeared at the end of June – the begging of July. The second generation of imagines could be observed at the end of July – the beginning of August. A part of the imagines migrated to overwintering sites without ovipositing approximately at the end of August. The overwintered beetles were observed to emerge on the Mongolian oak Q uercus mongolica, the greater celandine Chelidonium majus, and the bird cherry Prunus padus. A typical primary biotope of the potato ladybird beetle was a potato field at the stage of vegetative growth (5-7 leaves) surrounded by the couch grass Elymus repens, the common dandelion Taraxacum officinale, and the perennial sow-thistle Sonchus arvensis. Marking the overwintered and new generations of imagines showed that the presence of the potato ladybird beetle in an ecosystem depended on agricultural and agrometeorological conditions.

Melanin Synthesis Pathway Interruption: CRISPR/Cas9-mediated Knockout of dopa decarboxylase (DDC) in Harmonia axyridis (Coleoptera: Coccinellidae).

CRISPR/Cas9 technology is a very powerful genome editing tool and has been used in many insect species for functional genomics studies through targeted gene mutagenesis. Here, we successfully established CRISPR/Cas9 research platform in Asian multi-colored ladybird beetle, Harmonia axyridis, an important natural enemy in biological control. In this study, one pivotal gene dopa decarboxylase (DDC) in melanin synthesis was targeted by CRISPR/Cas9 to generate mutants in H. axyridis by CRISPR/Cas9 technology. Our results showed that injection of single guide RNA of the DDC and Cas9 protein into preblastoderm eggs induced one insertion and four deletion (indels) mutant H. axyridis. Mutations of HaDDC gene generated 25% mutant rate with melanin missing phenotype in larva, pupa,l and adult stage. The predation ability of the fourth instar larvae has no significant difference between wild (control) and mutant H. axyridis (G0), while these mutant fourth instar larvae had longer developmental period than that of the wild type. Consequently, the total predation of the fourth instar larvae was significantly increased in H. axyridis mutants comparing with the wild type. These results indicated that the success of CRISPR/Cas9 gene editing in H. axyridis. The gene editing platform in H. axyridis would facilitate the gene function research and promote special strain of predatory ladybird beetle generation.

Efficiency and Sustainability of Ips duplicatus (Coleoptera: Curculionidae) Pheromone Dispensers with Different Designs

Ips duplicatus (Coleoptera: Curculionidae) is a bark beetle that recently invaded southern Europe. It produces intense outbreaks in the spruce stands installed outside their natural area. Pheromone dispensers with different designs are used for monitoring this species. Compounds are released either by wick (ID Ecolure) or polyethene foil (ID RO and Pheagr IDU). We performed a series of laboratory and field experiments to compare the efficiency and sustainability of these dispensers in terms of pheromone release. The first experiment compared the Ips duplicatus capture dynamics between the ID Ecolure and ID RO in pheromones traps in three localities for 60 days. Release rates of used dispensers were evaluated in the same period. The second experiment analyzed headspace chemical composition in three dispensers (ID Ecolure, ID RO, Pheagr IDU) and tested their activity in pheromone traps. Active compounds content released by tested dispensers varied. The wick dispensers’ release rates (ID Ecolure) were strongly reduced from 365 to 50 mg/day within two weeks and then steadily to 16 mg/day after 60 days. Release rates of the polyethene dispensers (ID RO) remained constant over 60 days (20–24 mg/day). The highest initial emission was in the ID Ecolure. The ratio of pheromone components (ipsdienol/E-myrcenol) was lower for ID Ecolure (5) and ID RO (10) and higher for Pheagr IDU (565). In the field experiments, significantly more Ips duplicatus were caught with ID Ecolure than ID RO and Pheagr IDU in the first two weeks. Later, the attractivity of ID RO remained high, but captures by ID Ecolure were significantly reduced. The captures of Ips typograhus were also considered. We propose that the wick-type dispensers are a promising tool for controlling the hibernating beetle generation. The foil release dispensers can be used to monitor Ips duplicatus flight activity.

Application of Sarcosaprophagous Insects to Estimate the Postmortem Interval in 11 Cases.

Objective To test the feasibility and accuracy of with sarcosaprophagous insects postmortem interval （PMI） estimation with sarcosaprophagous insects and provide references for estimation practice. Methods Eleven cases confirmed by the detection results, with complete entomological evidence were selected. The insect species, estimation results and true results involved in the cases were statistically analyzed and compared. Results Thirteen species of insects were found at the criminal scene, including Chrysomya megacephala （Fabricius）, Chrysomya rufifacies （Macquart）, Chrysomya nigripes （Aubertin）, Lucilia sericata （Meigen）, Hydrotaea spinigera Stein, Muscina stabulans （Fallén）, Sarcophagid （species were not identified）, Megaselia scalaris （Loew）, Hermetia illucens （Linnaeus）, Saprinus splendens （Paykull）, Creophilus maxillosus （Linnaeus）, Dermestes maculatus （De Geer） and Necrobia ruficollis （Fabricius）. The PMI of all eleven cases was within the range of estimated PMI. The estimated results of 72.73% cases were on the same day of the true results. Conclusion Sarcosaprophagous insects can estimate the PMI simply and conveniently. In cases where the PMI is within the time range of one generation of flies or beetles, the estimation results are relatively accurate. However, the estimation is less accurate when the PMI is beyond the time range.

Habitat Quality Determines Dispersal Decisions and Fitness in a Beetle – Fungus Mutualism

Delayed dispersal of sexually mature offspring is a fundamental component of cooperative breeding. In ambrosia beetles, female offspring temporarily remain in their natal nest and refrain from reproduction, instead investing in alloparental care. Previous work has demonstrated a link between helping behaviour and the increased need for pathogen defence, arising from their close association with fungal cultivars. In the ambrosia beetle Xyleborinus saxesenii, mature female offspring can effectively fight pathogen infections and manage the microbial composition within the nest by adjusting the frequency of different hygienic and nest maintenance behaviours. This suggests a potential to respond flexibly to the ecology of their nest, which calls for a better understanding of the connection between behaviour and the microbial community thriving within their nests. Here, we studied the significance of the mutualistic fungus garden composition for the beetles’ nest ecology and fitness by experimentally varying substrate quality. We found that the vertically transmitted ambrosia fungus garden is composed of at least two fungus mutualist species and a wide variety of other microbes varying in their relative abundance. This is strongly affected by the moisture content of the substrate, which in nature depends on the age and type of wood. We found that the mutualist fungi complement each other in terms of dryness-resistance, allowing the beetles to utilise a broad range of substrates over prolonged time during which the wood gradually desiccates. Under suboptimal humidity conditions, the interaction between host and multiple fungus species has important ramifications for the behaviour of philopatric helpers, including their alloparental investment, sibling cannibalism and the timing of dispersal. Rearing five generations of beetles consecutively in dry substrate resulted in transgenerational effects on philopatry and alloparental care, probably mediated through the dominance of a particular fungus species that was driven by the experimental habitat condition. Interestingly, the nests of these selection lines produced much more offspring after five generations than any first-generation nest, which may have reflected increased egg laying by non-dispersing daughters. Our study highlights the importance of considering the interactions between the microbial community and their insect hosts for understanding social evolution in cooperatively breeding beetles.

Ips sexdentatus Mass-Trapping: Mitigation of Its Negative Effects on Saproxylic Beetles Larger Than the Target

Research Highlights: We investigated the negative effects of bark beetle mass trapping, especially non-target catches among the target’s natural enemies. Slot traps modified with mesh screen and escape windows were tested to improve their selectiveness. Background and Objectives: Two of the main natural enemies of bark beetles, Thanasimus formicarius (L.) and Temnoscheila caerulea (Olivier), are frequently trapped in high numbers in Ips sexdentatus (Böerner) pheromone traps, along with other saproxylic insects; this may lead to much larger pest populations in the successive 4–20 beetle generations. From 2016–2019, during I. sexdentatus mass-trapping in a pine forest of Tuscany (Italy), non-target catches were tallied. Trap modifications were evaluated to mitigate non-target catches, especially those concerning bark beetles’ natural enemies. Materials and Methods: A total of 25 bark-beetle slot traps were placed about 75 m apart in a pine stand infested by I. sexdentatus. Traps were baited with I. sexdentatus aggregation pheromone, whose main components are ipsenol, ipsdienol, and 2-methyl-3-buten-2-ol. Catches were collected every 10 days from March to December. In 2019, 13 traps were modified by applying a 6-mm mesh screen on top of the collection container and by providing three 60 mm × 8 mm escape windows immediately above the screen. These “modified traps” and their captures were considered separately from the 12 remaining “standard traps.” All bark beetle species were recorded, as well as all beetle species > 8 mm. Results: Overall, target catches amounted for <10% of the total beetle catches. The most-collected species was the bark beetle Orthotomicus erosus Wollaston. Trap modification allowed the escape of larger species, resulting in the reduction of the average size of caught specimens. Even though non-target catches among predators were still high, the proportion of major predators (T. formicarius and T. caerulea) to bark beetles showed a statistically significant reduction of predator catches in modified traps, an encouraging outcome. Conclusions: Trap modifications may mitigate the problem of non-target catches during mass trapping, especially reducing catches of beetle species larger than the target. However, the key is to schedule mass trapping only during those seasons when the target adults are more active than the main predator adults, thus limiting their catches and, consequently, the negative effects on pest management and biodiversity.

Disparity of Phoresy in Mesostigmatid Mites upon Their Specific Carrier Ips typographus (Coleoptera: Scolytinae).

Simple SummaryThis study investigated the phoretic relationship between mites and one of the most aggressive spruce bark beetles from Eurasia. During one season (April–September), bark beetles Ips typographus were collected with a specific synthetic aggregation pheromone. In the lab, we investigated the diversity of mites associated with I. typographus, mite preferences concerning the body parts of the beetles and how phoretic relationships change during the bark beetle’s flight season. Six phoretic mites species were found and 20% of beetles carried mites. Phoretic mite loads and the percent of beetles with mites were highest during the spring flight period. Phoretic mite species had specific preferences regarding their location on the body of the carrier.Ips typographus Linnaeus, 1758, the most important pest of Norway spruce (Picea abies Linnaeus, 1753) from Eurasia has damaged, in the last decades, a large area of forest in Romania. Associations between beetles and their symbiotic fungi are well known compared to beetle-mite relationships. The objectives of the study are to determine: (i) the diversity of mites species associated with I. typographus in a local outbreak from Central Romania; (ii) the mite’s preferences concerning the body parts of their carriers; and (iii) how phoresy changes during seasonal flight activity of the host. A total of 7896 adult I. typographus were analyzed and six mite species (both adults and immature stages) were found: Dendrolaelaps quadrisetus Berlese,1920, Proctolaelaps fiseri Samsinak, 1960, Trichouropoda polytricha Vitzthum, 1923, Histiostoma piceae Scheucher, 1957, Uroobovella ipidis Vitzthum, 1923, and Uroobovella vinicolora Vitzthum, 1926. Most mites were observed under the carriers’ elytra (46.8%), while 26.7% and 25.8% were seen on the thorax and elytral declivities, respectively. Mite phoresy peaked in the spring corresponding to the dispersal flight of the carrier. A smaller peak in phoresy occurred in the summer during the second beetle generation.

Life cycle of ground beetle Chlaenius tristis reticulatus Motschulsky, 1844 (Coleoptera: Carabidae) in the condition of Western Transbaikalia

In the conditions of Western Transbaikalia, Chlaenius tristis reticulatus Motschulsky, 1844 has a one-year late spring – early summer life cycle with the hibernation of a young generation of beetles. The interpretation of their life cycle is based on the study of sex and age-related structure of imago, the seasonal activity of generative females, the above-ground activity of larvae, and stages of the development of beetles in the laboratory conditions. The changes in the seasonal activity of beetles on meadows with different soil moisture (steppificated, moistened, and marshy meadows) were identified.

Роль метеорологічних чинників у зменшенні продукції верхівкового короїда в соснових деревостанах Східного Полісся

Інтенсивне поширення групових і куртинних осередків усихання в соснових насадженнях Східного Полісся розпочалося після дуже посушливої другої половини вегетаційного періоду 2016 р. та тривало протягом 2017–2018 рр., які вирізнялися екстремально посушливими умовами на початку вегетаційних періодів, коли гідротермічний коефіцієнт за Г. Т. Селяніновим становив 0,1–0,5, а дефіцит атмосферних опадів – 10–30 % у різні місяці. Після сприятливого для росту дерев початку вегетаційного періоду 2019 р. з гідротермічним коефіцієнтом 1,7 у результаті надлишку атмосферних опадів за пониженої температури поширення патологічного всихання сосняків у Східному Поліссі істотно знизилося та стабілізувалося з переважанням поодинокого та групового типів. Відновлення водозабезпечення дерев активізувало процеси смоловиділення, що інтенсивно перешкоджало спробам заселення дерев верхівковим короїдом на відносній висоті стовбура 0,51–0,75 і меншій. Середні значення продукції вздовж стовбурів заселених дерев становили від 29 до 33 шт.∙дм-2 молодих імаго.

Survival physiology and sex ratio of the Chinese white pine beetle Dendroctonus armandi (Coleoptera: Scolytinae) during host colonization and overwintering.

The Chinese white pine beetle Dendroctonus armandi (Coleoptera: Scolytinae) typically displays bivoltinism at altitudes below 1700 m in the Qinling Mountains, China. The periods of host colonization and larval overwintering are two important phases in the life cycle of bark beetles, as it is during these periods that they have to contend with host plant defences and periods of intense cold, respectively. Although during different seasons, the females and males of Chinese white pine beetles show varying tolerances to host plant terpenoids, the sex ratio and survival physiology condition of the two beetle generations are unknown. We investigated the sex ratio of individuals, and also examined the body mass, energy stores, and detoxication enzymes of males and females in each of the two generations in order to determine the overall population stability of each generation. We identified a female-biased sex ratio among adults in both generations. Furthermore, patterns of body mass, energy stores, and detoxication enzymes were found to differ between the two sexes and two seasons. Compared with the males, the females have a larger body mass and higher amounts of stored lipids, which are assumed to be adaptations designed to overcome host resistance and facilitate subsequent oviposition.

CLIMATIC FACTORS INFLUENCING THE VULNERABILITY OF SCOTS PINE TO BARK BEETLES ATTACKS IN THE CENTRAL POLISSYA

The aim of the research was to evaluate the changes of climate factors in Central Polissya, which can contribute to Scots pine vulnerability to bark beetle attacks and increase of their population density. In 2005–2018 an average annual and growing season air temperature increased, especially in the southern part of the region. On temperature conditions until 2009, multivoltine bark beetles were possible to develop only one full generation. Thermal conditions in Scots pine stands in the vicinity of 5 meteorological stations in 2010, three meteorological stations in 2012, two meteorological stations in 2015, one meteorological station in 2016, and five meteorological stations in 2018 were favorable for the development two bark beetle generations. Average growing season precipitation for 2005–2018 was inferior to the long-term data for all analyzed meteorological stations, except Olevsk. Average G. T. Selyaninov hydrothermal index value fell to the Forest-steppe “standard” in 2005 and 2009 and to the Steppe “standard” in 2015. Such a decrease is unfavorable for forest trees, which are adapted to the high humidity of air and soil.

Developmental parameters of a southern mountain pine beetle (Coleoptera: Curculionidae) population reveal potential source of latitudinal differences in generation time

AbstractMountain pine beetle (Dendroctonus ponderosaeHopkins; Coleoptera: Curculionidae) is a major disturbance agent in pine (PinusLinnaeus; Pinaceae) ecosystems of western North America. Adaptation to local climates has resulted in primarily univoltine generation time across a thermally diverse latitudinal gradient. We hypothesised that voltinism patterns have been shaped by selection for slower developmental rates in southern populations inhabiting warmer climates. To investigate traits responsible for latitudinal differences we measured lifestage-specific development of southern mountain pine beetle eggs, larvae, and pupae across a range of temperatures. Developmental rate curves were fit using maximum posterior likelihood estimation with a Bayesian prior to improve fit stability. When compared to previously published data for a northern population, optimal development of southern individuals occurred at higher temperatures, with higher development thresholds, as compared with northern individuals. Observed developmental rates of the southern and northern populations were similar across studied lifestages at 20 °C, and southern lifestages were generally faster at temperature extremes (10 °C, 27 °C). At 25 °C southern fourth instars were significantly slower than northern fourth instars. Our results suggest that evolved traits in the fourth instar and remaining unstudied lifestage, teneral (i.e., preemergent) adult, likely influence latitudinal differences in mountain pine beetle generation time.

Low intraspecific genetic diversity indicates asexuality and vertical transmission in the fungal cultivars of ambrosia beetles

Abstract Ambrosia beetles farm ascomycetous fungi in tunnels within wood. These ambrosia fungi are regarded asexual, although population genetic proof is missing. Here we explored the intraspecific genetic diversity of Ambrosiella grosmanniae and Ambrosiella hartigii (Ascomycota: Microascales), the mutualists of the beetles Xylosandrus germanus and Anisandrus dispar. By sequencing five markers (ITS, LSU, TEF1α, RPB2, β-tubulin) from several fungal strains, we show that X. germanus cultivates the same two clones of A. grosmanniae in the USA and in Europe, whereas A. dispar is associated with a single A. hartigii clone across Europe. This low genetic diversity is consistent with predominantly asexual vertical transmission of Ambrosiella cultivars between beetle generations. This clonal agriculture is a remarkable case of convergence with fungus-farming ants, given that both groups have a completely different ecology and evolutionary history.

Pre-treatment with salicylic acid induces phenolic responses of Norway spruce (Picea abies) bark to bark beetle (Ips typographus) attack

The temporal gradations of the investigated phenolics in Norway spruce bark after bark beetle (Ips typographus) attack followed the general eco-physiological concept. Treatment with salicylic acid inhibits bark beetle colonisation, alleviates the phenolic responses and activates the synthesis of condensed tannins on later sampling dates. Conifer bark is the target of numerous organisms due to its assimilated transport and nutrient storage functions. In the presented study, 100 mM salicylic acid (SA) was applied onto Norway spruce stems prior to being infested with bark beetles (Ips typographus L.), to study the temporal gradation of changes in condensed tannins (CT) and total phenolics (tPH) and their significance for mediating stress-tolerance. A significant accumulation of CT was monitored in untreated trees in response to progressive bark beetle infestation occurring from May onwards. In SA-treated infested trees, the CT values remained at control levels until May, but after the re-treatment of infested trees in June, the concentrations of CT rose significantly in comparison to the controls. The tPH values dropped 16 days after SA-treatment, independent of infestation, and later on remained at control level until July. In contrast, tPH contents accumulated in untreated infested trees in May, eased in June and increased again in July, when the trees were affected by the second generation of bark beetles. To sum up, in May and July when the highest beetle-flight activity was monitored the metabolic shift of phenolics within untreated infested trees differed significantly from the response of SA-treated trees. In addition, on SA-treated trees less entrance holes were monitored over the whole period of sampling when compared to untreated infested trees. These results provide evidence that SA-treatment alleviates the phenolic responses, activates the synthesis of condensed tannins and inhibits bark beetle colonisation.