Pine Sawyer Research Articles

Sexual size dimorphism affecting mate choice and reproduction in the pine sawyer beetle, Monochamus alternatus.

Monochamus alternatus is a notorious pest of the pine forests across East Asian countries. Both large and small individuals of either sex coexist in the wild. However, whether and how body size affects sexual selection outcomes and longevity remains unknown. In this study, we allowed a male or a female of small or large size to choose between two mates of varying sizes, which were from a wild-caught population. Our results revealed that mating latency and frequency of mating attempts varied across different social environments. Both large males and large females preferred larger mates, whereas this preference was not observed for the small males and small females. Male-male competition had no significant effect on ejaculation duration and frequency or sperm number in ejaculates. When a single male had an opportunity to choose between two females of different sizes, the reproductive investment of small males towards the small females was almost doubled compared to that of the large males, i.e., longer ejaculation duration, higher ejaculation frequency, and greater numbers of sperm transferred. However, the greater mating efforts of small males did not translate to greater fecundity/fertility of small females. We also showed that regardless of their body size, females always had greater fertility when they mated with large males but evidence for a trade-off between fecundity and longevity was not found. Alternatively, female fecundity was positively associated with longevity, and fertility was negatively associated with longevity and fecundity. We discussed these results placing it in a broader context of mate choice evolutionary dynamics.

Climate change may make pine wilt disease more prevalent

Abstract Pine wilt disease is one of the most severe and devastating diseases affecting pine forests worldwide, resulting in huge economic losses in many countries. The pinewood nematode (PWN), Bursaphelenchus xylophilus, is the causal agent of pine wilt disease and is obligately vectored by pine sawyer beetles, of the genus Monochamus. For the disease to be present, the habitat must be suitable for the PWN, and include at least one vector species, and at least one host species. To predict its potential distribution, a model must consider all three components. However, no comprehensive study has examined the influence of climatic suitability on the distribution of this “biological complex”. This study addresses this gap by incorporating biotic interactions, specifically involving 13 vectors and 61 host plants, into projections based on the PWN model. We predicted the global potential distribution of pine wilt disease and compared it with the PWN model to highlight the importance of including biotic interactions in species distribution models under climate change. We found that the model revealed an overall trend of increasing suitability scores for both the PWN and pine wilt disease models under future climate scenarios. Furthermore, compared to the PWN model, the biotic model results in an apparent increase in suitability worldwide in the future as the climate will be more suitable to vector and host complexes, suggesting that pine wilt disease could potentially spread to other places via available hosts and vectors. Synthesis and applications. By incorporating biotic interactions, we projected a more accurate suitable area for pine wilt disease, offering valuable insights into regions at high risk for future invasions by the disease and its vectors. This information supports the development of management and early detection strategies in areas of high suitability, helping to mitigate potential economic and ecological losses. Additionally, this study introduces a novel approach for integrating biotic factors into species distribution models.

Swift regulation of nicotinic acetylcholine receptors (nAChRs) and glutathione S-transferase (GST) enables the rapid detoxification of thiacloprid in pine sawyer beetles

Thiacloprid, a neonicotinoid insecticide, has become one of the major control agents for the pine sawyer beetle, Monochamus alternatus Hope, however, the mechanism of detoxification is unknown. We demonstrate that glutathione S-transferases (GSTs) and nicotinic acetylcholine receptors (nAChRs) are involved in the rapid detoxification of thiacloprid in M. alternatus larvae. The activity of detoxification enzyme GSTs was significantly higher, while the activity of acetylcholinesterase (AChE) was inhibited under thiacloprid exposure. The inhibition of AChE activity led to lethal over-stimulation of the cholinergic synapse, which was then released by the rapid downregulation of nAChRs. Meanwhile, GSTs were overexpressed to detoxify thiacloprid accordingly. A total of 3 nAChR and 12 GST genes were identified from M. alternatus, among which ManAChRα2 and MaGSTs1 were predicted to confer thiacloprid tolerance. RNA interference (RNAi) was subsequently conducted to confirm the function of ManAChRα2 and MaGSTs1 genes in thiacloprid detoxification. The successful knock-down of the ManAChRα2 gene led to lower mortality of M. alternatus under LC30 thiacloprid treatment, and the suppression of the MaGSTs1 gene increased the mortality rate of M. alternatus. However, the mortality rate has no significant difference with controls when thiacloprid was fed together with both dsMaGSTs1 and dsManAChRα2. Molecular docking modeled the molecular basis for interaction between MaGSTs1/ManAChR and thiacloprid. This study highlights the important roles that ManAChRα2 and MaGSTs1 genes play in thiacloprid detoxification through transcriptional regulation and enzymatic metabolization, and proposes a new avenue for integrated pest management that combines pesticides and RNAi technology as an efficient strategy for M. alternatus control.

Biomass-Based, Dual Enzyme-Responsive Nanopesticides: Eco-friendly and Efficient Control of Pine Wood Nematode Disease.

Pine wood nematode (PWN) disease is a globally devastating forest disease caused by infestation with PWN, Bursaphelenchus xylophilus, which mainly occurs through the vector insect Japanese pine sawyer (JPS), Monochamus alternatus. PWN disease is notoriously difficult to manage effectively and is known as the "cancer of pine trees." In this study, dual enzyme-responsive nanopesticides (AVM@EC@Pectin) were prepared using nanocoating avermectin (AVM) after modification with natural polymers. The proposed treatment can respond to the cell wall-degrading enzymes secreted by PWNs and vector insects during pine tree infestation to intelligently release pesticides to cut off the transmission and infestation pathways and realize the integrated control of PWN disease. The LC50 value of AVM@EC@Pectin was 11.19 mg/L for PWN and 26.31 mg/L for JPS. The insecticidal activity of AVM@EC@Pectin was higher than that of the commercial emulsifiable concentrate (AVM-EC), and the photostability, adhesion, and target penetration were improved. The half-life (t1/2) of AVM@EC@Pectin was 133.7 min, which is approximately twice that of AVM-EC (68.2 min). Sprayed and injected applications showed that nanopesticides had superior bidirectional transportation, with five-times higher AVM contents detected in the roots relative to those of AVM-EC when sprayed at the top. The safety experiment showed that the proposed treatment had lower toxicity and higher safety for nontarget organisms in the application environment and human cells. This study presents a green, safe, and effective strategy for the integrated management of PWN disease.

Heat stress-induced oviposition behavioral change correlates with sperm damage in the pine sawyer beetle, Monochamus alternatus.

Global climate change is causing an increase in extreme high temperatures (EHTs), which subject insects to unprecedented stress. Behavior plasticity in response to EHTs, particularly oviposition behavior, is important for the persistence and outbreak of insect populations. Investigating the plasticity of oviposition behavior and its underlying mechanisms has theoretical importance to pest management, but knowledge gaps still remain. Herein, we characterized the reproductive traits of Monochamus alternatus, a dominant insect vector of the destructive pine wilt disease, including oviposition behavioral patterns, fecundity, offspring fitness and sperm viability, under simulated heatwave conditions in the laboratory. The results showed that (i) EHTs induced a novel oviposition behavior, whereby females deposited multiple eggs into a single groove rather than laying one egg per groove under normal condition; (ii) EHTs exerted stage- and sex-specific effects on fecundity, offspring fitness and sperm viability; and (iii) there was a significant correlation between frequency of the novel oviposition strategy and sperm viability. We hypothesized that this beetle pest has the ability to flexibly shift towards a low-cost oviposition strategy to counteract the fitness costs caused by heat stress. Taken together, these findings provide a theoretical foundation for personalized pest management strategies in the context of climate change. © 2024 Society of Chemical Industry.

The Neurotranscriptome of Monochamus alternatus.

The Japanese pine sawyer Monochamus alternatus serves as the primary vector for pine wilt disease, a devastating pine disease that poses a significant threat to the sustainable development of forestry in the Eurasian region. Currently, trap devices based on informational compounds have played a crucial role in monitoring and controlling the M. alternatus population. However, the specific proteins within M. alternatus involved in recognizing the aforementioned informational compounds remain largely unclear. To elucidate the spatiotemporal distribution of M. alternatus chemosensory-related genes, this study conducted neural transcriptome analyses to investigate gene expression patterns in different body parts during the feeding and mating stages of both male and female beetles. The results revealed that 15 genes in the gustatory receptor (GR) gene family exhibited high expression in the mouthparts, most genes in the odorant binding protein (OBP) gene family exhibited high expression across all body parts, 22 genes in the odorant receptor (OR) gene family exhibited high expression in the antennae, a significant number of genes in the chemosensory protein (CSP) and sensory neuron membrane protein (SNMP) gene families exhibited high expression in both the mouthparts and antennae, and 30 genes in the ionotropic receptors (IR) gene family were expressed in the antennae. Through co-expression analyses, it was observed that 34 genes in the IR gene family were co-expressed across the four developmental stages. The Antenna IR subfamily and IR8a/Ir25a subfamily exhibited relatively high expression levels in the antennae, while the Kainate subfamily, NMDA subfamily, and Divergent subfamily exhibited predominantly high expression in the facial region. MalIR33 is expressed only during the feeding stage of M. alternatus, the MalIR37 gene exhibits specific expression in male beetles, the MalIR34 gene exhibits specific expression during the feeding stage in male beetles, the MalIR8 and MalIR39 genes exhibit specific expression during the feeding stage in female beetles, and MalIR8 is expressed only during two developmental stages in male beetles and during the mating stage in female beetles. The IR gene family exhibits gene-specific expression in different spatiotemporal contexts, laying the foundation for the subsequent selection of functional genes and facilitating the full utilization of host plant volatiles and insect sex pheromones, thereby enabling the development of more efficient attractants.

Developing an improved lure for attracting the pine sawyer beetle (Monochamus galloprovincialis) with reduced bycatch of predatory beetles

Abstract The pine sawyer beetle (Monochamus galloprovincialis) is a European vector of the invasive pinewood nematode (Bursaphelenchus xylophilus), one of the most dangerous threats to pine forests worldwide. One recommended method for detecting the nematode is catching and inspecting the M. galloprovincialis beetles. Effective commercial lures are available for that insect but attract non‐target species, particularly beneficial Thanasimus species. Our study aimed to develop an equally effective M. galloprovincialis lure less attractive to beneficial predatory insects. We used electroantennography to test several compounds occurring in the pheromones, hindgut extracts or headspace emissions of non‐Ips bark beetles. The compounds that caused the strongest antennal responses were used along with α‐pinene (host‐tree volatile) and monochamol (2‐undecyloxy‐1‐ethanol, a male‐produced aggregation pheromone of M. galloprovincialis) to prepare the lures for olfactometric and field testing. In the field experiments, the lure containing (+)‐α‐pinene, monochamol, (1R)‐(−)‐myrtenal and (S)‐(−)‐trans‐verbenol was equally effective as the commercial lure Galloprotect Pack. It attracted significantly less Thanasimus formicarius and T. femoralis beetles. Thus, the new lure can serve as a basis for developing an operational lure for monitoring M. galloprovincialis with reduced bycatch of predatory beetles.

Copulation Duration and Sperm Precedence with Reference to Larval Diapause Induction in Monochamus alternatus Hope (Coleoptera: Cerambycidae).

Adults of the pine sawyer Monochamus alternatus are the primary vector of Bursaphelenchus xylophilus, the causative agent of pine wilt disease. A sawyer subspecies in Taiwan (abbreviated 'T') has two generations a year (bivoltinism) due to facultative diapause, whereas another subspecies in Japan (abbreviated 'J') has a one- or two-year life cycle due to obligate diapause. T, with two infection periods a year, will cause more severe disease epidemics than J if it is introduced into Japan. Inter-subspecies hybridization may inhibit the expression of bivoltinism because many F1 hybrids induce diapause. To predict the effects of introducing T into Japan, the present study investigated copulation duration and late-male sperm precedence to fertilize eggs. The results indicated that a single copulation for more than 65 s supplied sufficient sperm to fertilize a lifetime production of eggs. The incidence of larval diapause was 0.15 for the offspring of T females that mated with a T male and increased to 0.292-0.333 after remating with a J male, while the incidence of larval diapause was 0.900-1.000 for hybrids from T females mated with a J male. Consequently, the estimated proportion of second-male sperm used by T females was 0.185-0.217. The effects of introducing T populations into Japan on the severity of disease epidemics were also discussed.

Identification of pine wood nematode (Bursaphelenchus xylophilus) loading response genes in Japanese pine sawyer (Monochamus alternatus) through comparative genomics and transcriptomics.

Pine wood nematode (PWN; Bursaphelenchus xylophilus) is the causative agent of pine wilt disease (PWD), which is considered the most dangerous biohazard to conifer trees globally. The transmission of PWN relies on insect vectors, particularly the Japanese pine sawyer (JPS; Monochamus alternatus). However, the molecular mechanism underlying PWN-JPS assembly remains largely unknown. Here, we found that both geographical and gender could significantly affect the PCA (PWN carrying amount) of JPS; thus, JPS transcriptomes from diverse locations and genders were explored regard to PWN loading. Due to the shortage of genomes, we developed a full-length reference transcriptome for analyzing next-generation sequencing data. A comparative genomic study was performed, and 11 248 potential PWN-carrying associate genes (β) were nominated in JPS by using the reported genomes of PWN and non-PWN carrier insect species. Then, 151 differentially expressed transcripts (DETs), 28 of them overlapped with β, correlated with the PCA of JPS were nominated by RNA-Seq, and found that fatty acid β-oxidation might be the key factor that affected the PCA of JPS. Furthermore, JPS fatty acid β-oxidation rates were experimentally decreased using the inhibitor Etomoxir, leading to an increased PCA of JPS. Meanwhile, silencing MaCPT1 in JPS by RNA interference led to a decreased fatty acid β-oxidation rate and increased PCA of JPS. In conclusion, MaCPT1 was able to decrease the PWN-JPS assembly formation through the fatty acid β-oxidation of JPS. These results provide new insights for exploring the impact of PWN invasion on JPS. © 2024 Society of Chemical Industry.

Enhancing pest control interventions by linking species distribution model prediction and population density assessment of pine wilt disease vectors in South Korea

Pine wilt disease caused by pinewood nematode is one of the most destructive forest diseases, and still spreading in South Korea despite the various control efforts. Japanese pine sawyer (JPS) and Sakhalin pine sawyer (SPS) are the main vectors of the disease. Understanding the distribution and density of the vectors is crucial since the control period is determined by the different emergence periods of the two vectors and the control method by its density and the expected damage severity. In this study, we predicted the distribution of JPS and SPS using Maxent and investigated the relationship between the resulting suitability value and the density. The population densities of JPS and SPS were obtained through a national survey using pheromone traps between 2020-2022. We converted the density data into presence/absence points to externally validate each species distribution model, then we used quantile regression to check the correlation between the suitability and population density, and finally we used three widely used thresholds to convert the model results into binary maps, and tested if they could distinguish the density by comparing the Rb value of biserial correlation. The quantile regression revealed a positive relationship between the habitat suitability and population density sampled in the field. Moreover, the binary map with threshold criteria that maximizes the sum of the sensitivity and specificity had the best density discrimination capacity with the highest Rb. A quantitative relationship between suitability and vector density measured in the field from our study provides reliability to species distribution model as practical tools for forest pest management.

Pine wilt disease: A global threat to forestry

AbstractPines are the most economically important trees in the world and, together with eucalyptus, they dominate commercial forests. But the success of a relatively small number of widely planted species, such as Pinus pinaster, the maritime pine, comes at a price. Pines are attractive to damaging pathogens and insect pests, including the pinewood nematode (PWN), Bursaphelenchus xylophilus, the causal agent of pine wilt disease (PWD). Originally described in Japan, PWD has caused widespread destruction to forests in countries such as China, Taiwan, Portugal, Spain and the United States. PWN causes irreparable damage to the vascular system of its pine hosts, leading to mortality within 3 months. Pine sawyer beetles (Monochamus spp.) are key vectors of PWD, introducing the PWN to healthy trees during feeding. Other organisms contribute to PWD spread and development, including bacteria, fungi and bark beetles. Control measures include tree felling to prevent vector transmission of PWN, insecticide treatments, trapping of Monochamus spp. and tree breeding for plant resistance. The PWN is a quarantine pathogen and subject to regular legislation and phytosanitary measures aimed at restricting movement and preventing introduction to new areas. Current research is investigating the use of biopesticides against PWN and Monochamus spp. This review examines the biology, epidemiology, impact and management of PWD through published research, grey literature and interviews with people directly involved in the management of the disease in Portugal.

Effects of temperature on reproduction and development of Cyanopterus ninghais (Hymenoptera: Braconidae), a larval parasitoid of Monochamus alternatus (Coleoptera: Cerambycidae)

AbstractCyanopterus ninghais (Hymenoptera: Braconidae), a newly discovered gregarious ectoparasitoid, is a promising biological control agent against the third‐fifth instar larvae of the Japanese pine sawyer, Monochamus alternatus (Coleoptera: Cerambycidae). Effects of constant ambient temperatures (17, 20, 23, 26, 29 and 32°C) on the reproduction and development of the parasitoid were determined in the laboratory. Results showed that the pre‐oviposition periods of C. ninghais decreased gradually with increasing temperatures, ranging from 8.5 d (at 17°C) to 3.4 d (at 32°C). Both the parasitism rates and the number of offspring exhibited a parabolic trend in relation to increasing temperatures, with the highest parasitism rate being 80% (at 29°C) and the maximum number of offspring reaching 7.2 (at 26°C). Temperature did not significantly affect the emergence rate and sex ratio of progeny. The duration of each developmental stage was inversely correlated with temperature within the range of 20 to 32°C. The egg‐to‐adult development time was 32.3 d at 20°C and 12.5 d at 32°C. The developmental threshold temperatures for the egg, larva, pupa, and the entire generation were 8.6, 12.6, 12.8 and 12.1°C, respectively, and the effective accumulated temperatures were 34.3, 51.3, 148.9 and 240.0 Degree‐days, respectively. We concluded that temperatures in the range of 26 to 29°C are the most suitable for the development and reproduction of C. ninghais. These findings provide important information for improving the artificial rearing efficiency and field release of this parasitoid under different temperature conditions.

The novel nematicide chiricanine A suppresses Bursaphelenchus xylophilus pathogenicity in Pinus massoniana by inhibiting Aspergillus and its secondary metabolite, sterigmatocystin.

Pine wilt disease (PWD) is responsible for extensive economic and ecological damage to Pinus spp. forests and plantations worldwide. PWD is caused by the pine wood nematode (PWN, Bursaphelenchus xylophilus) and transmitted into pine trees by a vector insect, the Japanese pine sawyer (JPS, Monochamus alternatus). Host infection by PWN will attract JPS to spawn, which leads to the co-existence of PWN and JPS within the host tree, an essential precondition for PWD outbreaks. Through the action of their metabolites, microbes can manipulate the co-existence of PWN and JPS, but our understanding on how key microorganisms engage in this process remains limited, which severely hinders the exploration and utilization of promising microbial resources in the prevention and control of PWD. In this study we investigated how the PWN-associated fungus Aspergillus promotes the co-existence of PWN and JPS in the host trees (Pinus massoniana) via its secondary metabolite, sterigmatocystin (ST), by taking a multi-omics approach (phenomics, transcriptomics, microbiome, and metabolomics). We found that Aspergillus was able to promote PWN invasion and pathogenicity by increasing ST biosynthesis in the host plant, mainly by suppressing the accumulation of ROS (reactive oxygen species) in plant tissues that could counter PWN. Further, ST accumulation triggered the biosynthesis of VOC (volatile organic compounds) that attracts JPS and drives the coexistence of PWN and JPS in the host plant, thereby encouraging the local transmission of PWD. Meanwhile, we show that application of an Aspergillus inhibitor (chiricanine A treatment) results in the absence of Aspergillus and decreases the in vivo ST amount, thereby sharply restricting the PWN development in host. This further proved that Aspergillus is vital and sufficient for promoting PWD transmission. Altogether, these results document, for the first time, how the function of Aspergillus and its metabolite ST is involved in the entire PWD transmission chain, in addition to providing a novel and long-term effective nematicide for better PWD control in the field.

Detection of Pine Wood Nematode Infestation Based on Improved YOLOv5

Pine wilt disease is a destructive forest disease caused by the parasitism of pine wood nematodes inside pine trees. Once infected, pine trees quickly wither and die due to the inability to drain water, hence it is also known as pine tree withering disease. It is mainly spread by pine sawyer beetles, with the characteristics of fast dissemination, rapid onset, and high mortality rate, making it a significant global plant disease. Failure to effectively control the pine wilt disease in a timely manner will result in the massive death of pine trees in a short period of time in forest areas. With the continuous development and popularization of artificial intelligence and UAV (Unmanned Aerial Vehicle) technology, combining various methods can timely detect diseased trees, and performing timely treatment and protection can greatly save the time and personnel costs of biological pest control. While it is also conducive to promoting the work of multiple related disciplines, such as bioengineering and greening engineering. In this paper, we first conducted a large number of aerial surveys on the forest area through UAV, collected relevant data, and preprocessed the obtained data, including data augmentation, cleaning, filtering, deduplication, formatting, etc., to ensure data quality and accuracy. Then, we labeled the data, and made certain improvements to the original YOLOv5. We added a new RRAM (Recurrent Residual Attention Module) to the original network model, which enables the network to timely focus on important information in redundant data, thus improving the network’s performance. Compared with the original YOLOv5, our network has a stronger performance.

Dynamic changes in the suitable areas for the pinewood nematode in the Sichuan-Chongqing Region of China.

The pine wood nematode (PWN), one of the largest alien forestry pests in China, has caused numerous deaths of conifer forests in Europe and Asia, and is spreading to other suitable areas worldwide. Information on the spatial distribution of the PWN can provide important information for the management of this species. Here, the current and future geographical distributions of PWN were simulated in the Sichuan-Chongqing region of China in detail based on the MaxEnt model. The results indicated excellent prediction performance, with an area under curve score of more than 0.9. The key factors selected were the altitude, maximum temperature of the warmest month, annual precipitation, precipitation of the wettest quarter, and minimum temperature of the coldest month, with thresholds of < 400 m, > 37.5 °C, 1100-1250 mm, 460-530 mm and > 4.0 °C, respectively, indicating that the PWN can live in low-altitude, warm, and humid areas. The suitable region for the PWN is mainly concentrated in the metropolitan area, northeast of Chongqing, and the southeastern and eastern parts of Sichuan Province. Most importantly, in addition to their actual distribution area, the newly identified suitably distribution areas A, B, C, and D for the coming years and E, F, G, and H for the period-2041-2060 (2050s) should be strictly monitored for the presence of PWNs. Altogether, the suitable distribution ranges of the PWN in the Sichuan-Chongqing region show an increasing trend; therefore, owing to its inability to disperse by itself, human activities involving pine trees and vectors of the Japanese pine sawyer should be intensively controlled to prevent the PWN from spreading to these newly discovered suitable areas.

The Temperature-Dependent Functional Response and Mutual Interference of Cyanopterus ninghais (Hymenoptera: Braconidae) Parasitizing Monochamus alternatus (Coleoptera: Cerambycidae)

Cyanopterus ninghais (Hymenoptera: Braconidae) is a newly discovered parasitoid on the 3rd-5th instar larvae of the Japanese pine sawyer, Monochamus alternatus (Coleoptera: Cerambycidae). We investigated the functional response of C. ninghais at three temperatures (20, 25, and 30 °C) and examined mutual interference. Results showed that C. ninghais had a Holling Type II functional response at all temperatures. By increasing the density of the M. alternatus larvae, the number of parasitized larvae increased until a maximum was reached. The parasitoid was most effective (a′/Th) at 30 °C (0.270) and an individual female wasp’s attack rate (a′) was 0.158, the handling time (Th) was 0.587, and the maximum theoretical parasitization rate per day (T/Th) was 11.927. However, the per capita parasitized level and per capita searching efficiency decreased significantly when the parasitoid density ranged from one to five. These findings suggest that intraspecific mutual interference and competition occur when multiple females search for a host in the same area. This study demonstrates that C. ninghais serves as an effective biocontrol agent, displaying strong control capabilities against M. alternatus larvae, with the potential for further development in the context of biological pest management targeting M. alternatus.

Bursaphelenchus mucronatus (Nematoda: Parasitaphelenchidae) associated with Monochamus galloprovincialis from Bosnia and Herzegovina and Georgia.

Bursaphelenchus mucronatus was detected in association with the pine sawyer beetle (Monochamus galloprovincialis) during the implementation and testing of cross traps with insect attractants as an efficient tool for detection survey for pine wood nematode (Bursaphelenchus xylophilus) in Bosnia and Herzegovina and Georgia in 2017 and 2018, respectively. This nematode was characterized by morphological, morphometric and molecular features. This is the first report of B. mucronatus in association with a M. galloprovincialis in Bosnia and Herzegovina and in Georgia.

Functional importance of groups I and II chitinases in cuticle chitin turnover during molting in a wood-boring beetle, Monochamus alternatus

Insects must periodically replace their old cuticle/exoskeleton with a new one in a process called molting or ecdysis to allow for continuous growth through sequential developmental stages. Many RNA interference (RNAi) studies have demonstrated that certain chitinases (CHTs) play roles in this vital physiological event because knockdown of these CHT genes resulted in developmental arrest during the ensuing molting period in several insect species. In this research we analyzed the functions of group I (MaCHT5) and group II (MaCHT10) CHT genes in molting of the Japanese pine sawyer, Monochamus alternatus, an important forest pest known as a major vector of the pinewood nematode. Real-time qPCR revealed that these two CHT genes differ in their expression patterns during late stages of development. Depletion of either MaCHT5 or MaCHT10 transcripts by RNAi resulted in lethal larval-pupal and pupal-adult molting defects depending on the double-stranded RNA (dsRNA) injection timing during development. The insects were unable to shed their old cuticle and died. Furthermore, transmission electron microscopic analysis revealed that, unlike dsEGFP-treated controls, dsMaCHT5- and dsMaCHT10-treated pharate adults exhibited a failure of degradation of the endocuticular layer of their old pupal cuticle, retaining nearly intact horizontal chitinous laminae and vertical pore canal fibers. Both enzymes were indispensable for complete turnover of the chitinous old endocuticle, which is critical for insect molting. The possible functions of two spliced variants of MaCHT10, namely, MaCHT10a and MaCHT10b, are also discussed. Our results add to the knowledge base for further functional studies of insect chitin catabolism by revealing the relative importance of both MaCHT5 and MaCHT10 in chitin turnover with subtle differences in their action. These essential genes and their encoded proteins are potential targets to manipulate for controlling populations of M. alternatus and other pest insects.

Hypoxia-induced tracheal elasticity in vector beetle facilitates the loading of pinewood nematode.

Many pathogens rely on their insect vectors for transmission. Such pathogens are under selection to improve vector competence for their transmission by employing various tissue or cellular responses of vectors. However, whether pathogens can actively cause hypoxia in vectors and exploit hypoxia responses to promote their vector competence is still unknown. Fast dispersal of pinewood nematode (PWN), the causal agent for the destructive pine wilt disease and subsequent infection of pine trees, is characterized by the high vector competence of pine sawyer beetles (Monochamus spp.), and a single beetle can harbor over 200,000 PWNs in its tracheal system. Here, we demonstrate that PWN loading activates hypoxia in tracheal system of the vector beetles. Both PWN loading and hypoxia enhanced tracheal elasticity and thickened the apical extracellular matrix (aECM) of the tracheal tubes while a notable upregulated expression of a resilin-like mucin protein Muc91C was observed at the aECM layer of PWN-loaded and hypoxic tracheal tubes. RNAi knockdown of Muc91C reduced tracheal elasticity and aECM thickness under hypoxia conditions and thus decreasing PWN loading. Our study suggests a crucial role of hypoxia-induced developmental responses in shaping vector tolerance to the pathogen and provides clues for potential molecular targets to control pathogen dissemination.

Different responses of Monochamus galloprovincialis and three non-target species to trap type, colour, and lubricant treatment

With the increasing threat to forests in Europe from the invasive pine wood nematode (PWN) Bursaphelenchus xylophilus, effective methods are needed to monitor and reduce populations of its insect vector, the pine sawyer beetle Monochamus galloprovincialis. In the present study, we tested the effectiveness of different trap types (multiple-funnel, cross-vane, and triangular), colours (black, white and clear), and lubricant (polytetrafluoroethylene, PTFE) treatments (different PTFE formulations and timing of trap treatment) on the catches of M. galloprovincialis and three most commonly captured non-target beetle species (the xylophagous Spondylis buprestoides and two predators, Thanasimus formicarius and T. femoralis) in Poland. Of the traps not treated with PTFE, the white and black 6-funnel traps were most effective in trapping M. galloprovincialis beetles, while the catches in the cross-vane traps (both white and clear) were low. Trap treatment with PTFE significantly increased trap effectiveness, regardless of PTFE type and time of application. The catches of S. buprestoides were affected by trap type, while those of T. formicarius depended on trap colour and size. Both species seem to respond positively to ethanol and/or α-pinene in the lure composition. PTFE treatment had a significant effect on the catches of T. femoralis. In conclusion, for the monitoring of M. galloprovincialis, we recommend the white cross-vane traps treated with dry PTFE. They are less but still effective in catching the target species, while their use, together with lures containing no ethanol and α-pinene, greatly reduces the catches of non-target insects S. buprestoides and T. formicarius.