Transmission of Bursaphelenchus xylophilus between Monochamus alternatus and Monochamus saltuarius through interspecific mating behaviour

Cerambycid adults of the genus Monochamus transmit the pine wood nematode (Bursaphelenchus xylophilus [Steiner et Buhrer] Nickle), the causative agent of pine wilt disease. To confirm the transmission of B. xylophilus between vector species, nematode‐infected Monochamus alternatus Hope and nematode‐free Monochamus saltuarius (Gebler) adults were paired and their behaviour was observed for 107–220 min. In three pairs that exhibited mounting without copulation, nematode transmission occurred, whereas it was not found in another pair without mountings. The effect of nematode transmission between different vector species on the invasion biology of B. xylophilus is discussed.     

Dispersal capacity of Monochamus galloprovincialis,the European vector of the pine wood nematode,on flight mills

The pine wood nematode (Bursaphelenchus xylophilus), which causes the symptoms of pine wilt disease, is recognized worldwide as a major forest pest. It was introduced into Portugal in 1999. It is transmitted between trees almost exclusively by longhorn beetles of the genus Monochamus, including, in particular, M. galloprovincialis (Coleoptera: Cerambycidae) in maritime pine forests. Accurate estimates of the flight capacity of this insect vector are required if we are to understand and predict the spread of pine wilt disease in Europe. Using computer‐linked flight mills, we evaluated the distance flown, the flight probability and speed of M. galloprovincialis throughout adulthood and investigated the effects of age, sex and body weight on these flight performances, which are proxies for dispersal capacity. The within‐population variability of flight performance in M. galloprovincialis was high, with a mean distance of 16 km flown over the lifetime of the beetle. Age and body weight had a significant positive effect on flight capacity, but there was no difference in performance between males and females. These findings have important implications for managing the spread of the pine wood nematode in European forests.     

Application of harmonic radar to analyze dispersal behavior of the Japanese pine sawyer beetle,Monochamus alternatus (Coleoptera: Cerambycidae)

Monochamus alternatus (Hope) is a severe wood‐boring pest in coniferous forests and a major vector of pine wilt disease in East Asia. Harmonic radar is a powerful tool for studying the dispersal behavior of insects and it could be applied to control pine wilt disease. In this study, we validated the application of harmonic radar for analyzing the dispersal behavior of M. alternatus beetles in a field environment. We determined the wing capacities of the beetles and the effects of electronic tagging and marking on their movement, flight ability, survivorship, and food consumption in the laboratory to confirm the suitability of this technique. The detection rate and recovery rate for beetles were analyzed separately using radar on caged pine stands and in the field environment. The results showed that the minimum wing capacity of the Japanese pine sawyer was 24.9 mg, which was seven times the weight of the electronic tag (3.5 mg). Marking and tagging the beetles had no significant adverse effects on their movement, flight capacity, food consumption, and survivorship. The detection rate using the radar system and recovery rate based on visual observations of the beetles in caged pines were both 95.6%. However, in the field environment, the detection and recovery rates were only 55.6% and 37.8% after one week, respectively, and 33.3% and 7.8% after two weeks. Harmonic radar is a promising technique for studying the dispersal behavior of the Japanese pine sawyer, but its performance is not satisfactory and major improvements are required for both the radar system and electronic tags.     

Newly Discovered Transmission Pathway of Bursaphelenchus xylophilus from Males of the Beetle Monochamus alternatus to Pinus densiflora Trees via Oviposition Wounds

The transmission of Bursaphelenchus xylophilus from Monochamus alternatus males to Pinus densiflora trees via oviposition wounds has been determined. Nematode-infested males, with mandibles fixed experimentally to prevent feeding, were placed for 48 hours with pine bolts containing oviposition wounds that had been made by nematode-free females. After removal of the nematode-infested males, the pine bolts were held for 1 month and then examined for the presence of nematodes. Reproducing nematode populations were recovered from pine bolts that were exposed to male beetles carrying a high number of nematodes. No reproducing nematode population could be recovered from pine bolts exposed to beetles with a small number of nematodes. Nematode reproduction in the pine bolts was not related to the number of oviposition wounds per bolt. Fourth-stage dispersal B. xylophilus juveniles, collected from beetle body surfaces, were inoculated on pine bolt bark 0, 5, 10, and 15 cm away from a single artificial, small hole. These dauer juveniles successfully entered some bolts. The probability of successful nematode reproduction decreased with increased distance between inoculation point and artificial hole. The results indicated that B. xylophilus can move a significant distance to oviposition wounds along the bark surface and enter a tree via the wounds. The new transmission pathway is considered important for the nematode to persist in pine forests such as in North America where pine wilt disease does not occur.     

The bimodal adult activity of Monochamus alternatus (Coleoptera: Cerambycidae) caught in pheromone traps in Jeju can be explained by the competitive attractiveness of dying pine trees

The Japanese pine sawyer, Monochamus alternatus Hope (Coleoptera: Cerambycidae), is known to be the primary vector of pinewood nematode Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle that causes pine wilt disease. Adult activity of M. alternatus caught in a pheromone trap on Jeju Island of Korea showed a bimodal form with the first peak in mid to late June and the second peak in mid to late September. The two peaks were separated between mid and late August, showing a valley. Accumulated degree‐days predicted that the emergence of the second generation adults could be possible just before the second peak. But actually no adults of the second generation occurred in the field development experiments of M. alternatus in 2016 and 2017. Pine trees without oleoresin flow (namely dying trees by the infection of pinewood nematode) were abundant during early July to early August. The bimodal adult activity pattern of M. alternatus could be partially explained by the competitive attractiveness of dying trees against pheromone traps, when we accepted the assumption that dying pine trees attract strongly M. alternatus.     

Optimization of a solid culture medium based on Monochamus alternatus for Cordyceps militaris fruiting body formation

Monochamus alternatus (Coleoptera: Cerambycidae; M. alternatus), popularly known as the Japanese pine sawyer, is a vector of pinewood nematode (Bursaphelenchus xylophilus) that causes pine wilt disease. A solid medium culture with M. alternatus produced Cordyceps militaris fruiting bodies with the longest strips and the highest biological efficiency. Supplementing the original form of M. alternatus with oats resulted in slightly enhanced fruiting body production. The original form of M. alternatus showed higher production than its powder form. The solid culture medium was optimized using a response surface methodology, and the optimal medium contained the following: 8·5 g per bottle of M. alternatus and 11·5 g per bottle of oats mixed with 22·4 ml of water in a 300-ml cylindrical plastic bottle. The optimal culturing period for the fruiting body formation was 37·1 days. Under these conditions, a fruiting body dry weight of 38·0 g per bottle (actual value) was attained. The fruiting body produced using a solid culture medium based on M. alternatus had a cordycepin content of about 25 µg g⁻¹. The solid culture medium containing M. alternatus is highly efficient and eco-friendly, and its effectiveness in large-scale fruiting body production from C. militaris has been demonstrated.     

Temperature Effects on the Transmission of Bursaphelenchus xylophilus (Nemata: Aphelenchoididae) by Monochamus alternatus (Coleoptera: Cerambycidae)

The object of this research was to investigate the effects of ambient temperature on the transmission of the pinewood nematode, Bursaphelenchus xylophilus, by its vector, Monochamus alternatus. Ninety M. alternatus were reared individually at one of three constant temperatures (16, 20, and 25 °C). As the ambient temperature decreased from 25 to 16 °C, longevity of vectors decreased, nematode transmission efficiency decreased, and the peak period of nematode transmission was delayed and its peak height decreased. Low temperature may inhibit the transmission process, and this inhibition could be partially responsible for preventing pine wilt disease from devastating pine forests in cool regions.     

A Nondestructive Method of Determining Bursaphelenchus xylophilus Infestation of Monochamus spp. Vectors

Pine wilt is caused by the nematode Bursaphelenchus xylophilus, which is transported to host trees in the trachea of Monochamus spp. (Coleoptera: Cerambycidae). The study of the relationship between the nematode and its beetle vectors has been hampered by the inability to estimate nematode presence or density within live beetles. This report describes a rapid method for estimating nematode load within live M. carolinensis and M. alternatus by visual examination of the atrium of the first abdominal spiracle. Visual estimates of nematode numbers correlated highly with actual nematode numbers. This method is a timesaving technique for determining relative numbers of B. xylophilus in pine wilt research.     

Spread of the pinewood nematode vectored by the Japanese pine sawyer: modeling and analytical approaches

The pinewood nematode, Bursaphelenchus xylophilus, is the causative agent of pine wilt of Pinus thunbergii and P. densiflora in Japan. The nematode is vectored by cerambycid beetles of the genus Monochamus. It is inferred to have been introduced from North America early in the 1900s and then to have distributed in China, Korea, and Taiwan. Intensive and/or long-term studies of pine wilt systems have elucidated the pattern and mechanism of the nematode’s spread within a pine stand, dispersal of vector beetles, and spread pattern of pine wilt within a prefecture. The modeling of nematode spread over pine stands, which involves beetle reproduction within a pine stand, has been developing and should elucidate the factors influencing the rate at which the nematode range expands. In this review, we summarize the biologies of the nematode, beetle, and tree, and then characterize the spread of the nematode within a pine stand, locally over pine stands, and regionally over unit administrative districts. Local and regional spreading of the nematode is related primarily to long-distance dispersal by insect vectors and to the artificial transportation of pine logs infested with the nematode and its vector, respectively.     

Geographical variation in seasonality and life history of pine sawyer beetles Monochamus spp: its relationship with phoresy by the pinewood nematode Bursaphelenchus xylophilus

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Modeling the Expansion of an Introduced Tree Disease

Pine wilt disease is caused by the introduced pinewood nematode, Bursaphelenchus xylophilus, for which the vector is the pine sawyer beetle, Monochamus alternatus. Native Japanese pines, black pine (Pinus thunbergii) and red pine (P. densiflora), are extremely sensitive to the nematode's infection, and the parasite has been expanding nationwide in the last few decades, despite intensive control efforts. To understand the parasite's range expansion in Japan, we modeled the dynamics of the pines and the beetle that disperses the nematode, using an integro-difference equation in a one-dimensional space. Based on field data collected in Japan, we investigated the dependence of the parasite's rate of range expansion on the eradication rate of the beetle, the initial pine density, and the beetle dispersal ability. Our model predicts several results. (1) The Allee Effect operates on beetle reproduction, and consequently the parasite cannot invade a pine stand, once the beetle density decreases below a threshold. (2) The distribution of the dispersal distance of the beetles critically affects the expansion rate of the disease. As the fraction of the beetles that travel over long distance increases from zero, the range expansion accelerates sharply. (3) However, too frequent long-range dispersal results in a failure of the parasite invasion due to the Allee Effect, suggesting the importance of correctly assessing the beetle's mobility to predict the speed of range expansion of the parasite. (4) As the eradication rate is increased, the range expansion speed decreases gradually at first and suddenly drops to zero at a specific value of the eradication rate. This revised version was published online in July 2006 with corrections to the Cover Date.     

Physiological development and dispersal ability of newly emerged Monochamus galloprovincialis

Novel associations between exotic pathogens and native insects may result in major ecological and economical losses. In Europe, Monochamus galloprovincialis (Olivier) (Coleoptera: Cerambycidae) is the only known vector of the exotic pine wood nematode Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle (Nematoda: Aphelenchoididae), the causal agent of pine wilt disease (PWD). Transportation of goods containing nematode‐infested beetles is the main pathway for the spread of the disease. In this scenario, management actions involving early detection and eradication are critical to stop further spread by the vector. Although dispersal of mature M. galloprovincialis has been successfully tracked using commercial baits and traps, dispersal ability of immature individuals is poorly understood. Sexual maturation and other physiological traits related to dispersal were studied for newly emerged M. galloprovincialis after different shoot‐feeding spans. Sexual maturation was complete after on average 12 (males) or 13 (females) feeding days. Monochamus galloprovincialis adults emerged with an average of 10% lipid and 23.8% (males) or 29.9% (females) pterothorax muscle content, and these percentages did not change significantly during shoot feeding. Microtomography images of wing muscle structures at different maturation stages confirmed these results. Emerged adults that were kept unfed survived an average of 12 days in the lab. The ability of unfed immature insects to fly through hostless terrain was studied by marking and releasing newly emerged insects from a crop area located up to 3 km away from two small pine stands. The longest flown distance recorded was 2 km. Fitted regressions indicated that immature insects could have travelled up to 3 109 m to reach the experimental stands. We found that M. galloprovincialis emerge with well‐developed thoracic muscles and energy reserves that enable them to sustain long flights over non‐forested areas. These findings should aid managers and policy makers in devising sound procedures in areas where the risk of introducing PWD is high.     

Synergistic attraction of pine sawyer Monochamus saltuarius (Coleoptera: Cerambycidae) to monochamol and α‐pinene

Monochamus (Coleoptera: Cerambycidae) species are longhorn pine sawyers that serve as insect vectors of the pinewood nematode Bursaphelenchus xylophilus (Nematoda: Parasitaphelenchidae), which are responsible for debilitating pine wilt disease. An aggregation pheromone, 2‐(1‐undecyloxy)‐1‐ethanol (hereafter referred to as monochamol), was shown to be effective at attracting Monochamus species. However, attraction of the pine sawyers to aggregation pheromones varied depending on semiochemicals, including host plant volatiles and kairomones. In this study, we investigated the abilities of monochamol and the host‐plant volatiles α‐pinene and ethanol to attract M. saltuarius in a pine forest in Cheongsong, Gyeongsangbuk‐do, Korea. A total of 91 M. saltuarius (28 males and 63 females) were captured. The combination of monochamol (700 mg) with α‐pinene and ethanol exhibited a synergistic effect on attracting M. saltuarius (11.0 beetles per trap), whereas monochamol alone and a mixture of α‐pinene and ethanol resulted in the capture of 3.2 beetles and 3.6 beetles per trap, respectively. Our results suggest that multi‐funnel traps baited with a blend of monochamol, α‐pinene and ethanol are highly effective for monitoring M. saltuarius and M. alternatus in pine forests.     

Bacteria associated with the pinewood nematode <Emphasis Type="Italic">Bursaphelenchus xylophilus</Emphasis> collected in Portugal

In this study, we report on the bacterial community associated with the pinewood nematode Bursaphelenchus xylophilus from symptomatic pine wilted trees, as well as from long-term preserved B. xylophilus laboratory collection specimens, emphasizing the close bacteria–nematode associations that may contribute to pine wilt disease development.     

Individual-based modeling of the spread of pine wilt disease: vector beetle dispersal and the Allee effect

Pine wilt disease is caused by the pinewood nematode Bursaphelenchus xylophilus, which is vectored by the Japanese pine sawyer beetle Monochamus alternatus. Due to their mutualistic relationship, according to which the nematode weakens and makes trees available for beetle reproduction and the beetle in turn carries and transmits the nematode to healthy pine trees, this disease has resulted in severe damage to pine trees in Japan in recent decades. Previous studies have worked on modeling of population dynamics of the vector beetle and the pine tree to explore spatial expansion of the disease using an integro-difference equation with a dispersal kernel that describes beetle mobility over space. In this paper, I revisit these previous models but retaining individuality: by considering mechanistic interactions at the individual level it is shown that the Allee effect, an increasing per-capita growth rate as population abundance increases, can arise in the beetle dynamics because of the necessity for beetles to contact pine trees at least twice to reproduce successfully. The incubation period after which a tree contacted by a first beetle becomes ready for beetle oviposition by later beetles is crucial for the emergence of this Allee effect. It is also shown, however, that the strength of this Allee effect depends strongly on biological mechanistic properties, especially on beetle mobility. Realistic individual-based modeling highlights the importance of how spatial scales are dealt with in mathematical models. The link between mechanistic individual-based modeling and conventional analytical approaches is also discussed.     

A new parasitoid (Hymenoptera: Braconidae) of <Emphasis Type="Italic">Monochamus alternatus</Emphasis> (Coleoptera: Cerambycidae) in China

Bracomorpha ninghais sp. n. (Hymenoptera: Braconidae) is described and illustrated based on individuals reared from the immature stages of the pine sawyer Monochamus alternatus (Coleoptera: Cerambycidae) in Zhejiang of China, which is considered a notorious forest pest associated with the main vector of the pine wood nematode Bursaphelenchus xylophilus (Nematoda: Aphelenchoididae) in China.     

Canopy-related adult density and sex-related flight activity of Monochamus alternatus (Coleoptera: Cerambycidae) in pine stands

Monochamus alternatus Hope is an important vector of the pinewood nematode Bursaphelenchus xylophilus (Steiner et Buhrer) Nickle, which causes pine wilt disease. To determine canopy-related differences in the activity density of M. alternatus adults in pine stands, sticky screen traps with no lure were suspended under and in the canopy at 3.8 and 10 m above the ground of a Pinus densiflora Siebold et Zuccarini stand during a flight season. The five upper and five lower traps caught 338 and 54 adults, respectively, during a flight season from 9 June to 12 October 2011, indicating that activity density was six times as high in the canopy as under it. Male-biased sex ratio was observed for trap catches during a season: The sex ratio was male-biased in the early half of the flight season and 1:1 in the late half. There was no difference in sex ratio between the inside and outside of the canopy. To determine the sex-related difference in flight activity, the adults were captured by two different measures in two other mixed stands of P. densiflora and P. thunbergii Parlatore. Kicking tree trunks to cause beetles to drop revealed a 1:1 sex ratio of catches, whereas sticky screen traps tended to show a male-biased sex ratio in a 4-year study, suggesting that males were more active fliers than females.     

Applying a spread model to identify the entry points from which the pine wood nematode, the vector of pine wilt disease, would spread most rapidly across Europe

Pine wilt disease, which can rapidly kill pines, is caused by the pine wood nematode, Bursaphelenchus xylophilus. It is expanding its range in many countries in Asia and measures are being taken at the EU level to prevent its spread from Portugal. Due to the threat to European forests, it is important to prevent additional introductions and target surveillance to the points of entry that pose the greatest risk. In this study, we present a model to identify the European ports from which the nematode can spread most rapidly across Europe. This model describes: (1) the potential spread of the pine wood nematode based on short-distance spread (the active flight of the vector beetles) and long-distance spread (primarily due to human-mediated transportation), and (2) the development of pine wilt disease based on climate suitability and the potential spread of the nematode. Separate introductions at 200 European ports were simulated under various climate change scenarios. We found that the pine wood nematode could invade 19–60% of the study area (30°00 N–72°00 N, 25°00 W–40°00 E) by 2030, with the highest spread from ports located in Eastern and Northern Europe. Based on climate change scenarios, the disease could affect 8–34% of the study area by 2030, with the highest spread from ports located in South-Eastern Europe. This study illustrates how a spread model can be used to determine the critical points of entry for invasive species, so that surveillance can be targeted more accurately and control measures prioritised.     

Current Research on the Major Nematode Problems in Japan

Among important nematode species occurring in Japan, current research achievements with the following four nematodes are reviewed: 1) Soybean cyst nematode (SCN), Heterodera glycines - breeding for resistance, race determination, association with Cephalosporium gregatum in azuki bean disease, and isolation of hatching stimulant. 2) Potato-cyst nematode (PCN), Globodera rostochiensis - pathotype determination (Ro 1), breeding for resistance, and control recommendations. 3) Pinewood nematode (PWN), Bursaphelenchus xylophilus - primary pathogen in pine wilt disease, life cycle exhibiting a typical symbiosis with Japanese pine sawyer, Monochamus alternatus, and project for control. 4) Rice root nematodes (RRN), Hirschmanniella imamuri and H. oryzae - distribution of species, population levels in roots, and role of these nematodes in rice culture.