Platypus Koryoensis Research Articles

Oak Decline Syndrome in Korean Forests: History, Biology, and Prospects for Korean Oak Wilt

Oak decline syndrome has been observed in South Korea and Japan and variously referred to as Korean oak wilt (KOW) and Japanese oak wilt (JOW). We reviewed aspects of the historical occurrence of KOW, disease cycle, and its potential causes. KOW has been seen principally in Mongolian oak (Quercus mongolica Fisch. ex Ledeb.). The first occurrence of KOW was in 2004 in Seongnam, South Korea. KOW is associated with the fungus Raffaelea quercus-mongolicae, which is vectored by the ambrosia beetle Platypus koryoensis. In addition, it has been suggested that yeasts have evolved a symbiotic relationship with the vector without antagonism for the pathogenic fungus. The number of trees in Korea killed by KOW increased to about 331,000 in 2011, but then decreased to about 157,000 in 2019. We hypothesized that trees infected by R. quercus-mongolicae accumulate phenolic compounds in the sapwood and the vector (P. koryoensis) beetles then avoid these trees. Therefore, the number of hosts available for the beetle after a KOW outbreak decrease due to accumulation of phenolic compounds in the wood, although most oak trees survive outbreaks. Therefore, P. koryoensis beetles move longer distances after outbreaks to find susceptible host trees. Novel occurrence of KOW in Korea may be due to either (1) an increase in tree age (size) in Korean oak stands, for which the beetle has a known preference or (2) climate change, which may be increasing the number of weakened or stressed trees, for which P. koryoensis also shows a preference.

Population genetic structure of Raffaelea quercus‐mongolicae indicates a recent fungal introduction event to Jeju Island from inland areas of South Korea

AbstractRaffaelea quercus‐mongolicae, a mycangial symbiont of a wood‐boring ambrosia beetle, Platypus koryoensis (Coleoptera: Curculionidae: Platypodidae), has been associated with the mass mortality of Korean oak trees in South Korea. Systemic wilt from the inoculation of oak trees with R. quercus‐mongolicae has caused significant damage to forest ecosystems in the country. Despite the continued spread of this fungus across the country since the first discovery of the disease, little is known regarding its biology. During a recent survey carried out to investigate the status of oak wilt diseases on Jeju Island, South Korea, visible signs of bark beetle attack, including bark beetle frass and galleries, were consistently observed in Quercus serrata, and R. quercus‐mongolicae was successfully recovered from the trees. To determine whether the pathogen was introduced from inland areas of the country to Jeju Island, the genetic diversity and population structure of R. quercus‐mongolicae isolates collected from various geographical regions and hosts in the country were investigated using a combination of eight microsatellite markers designed from the genome of the fungus in this study. The results showed lower levels of genetic diversity for the population from Jeju Island compared to those from inland areas of the country. This suggests that a limited number of individuals were recently introduced to Jeju Island, resulting in a new disease problem in the area.

Investigation of the mating‐type distribution of Raffaelea quercus‐mongolicae in South Korea

AbstractRaffaelea quercus‐mongolicae is a mycangial symbiont of a wood‐boring ambrosia beetle, Platypus koryoensis (Coleoptera: Curculionidae: Platypodidae), which is believed to be associated with oak mortality in South Korea. Since the first discovery of the disease in 2004, oak mortality has continued to spread across the country, and the pathogen has had a significant impact on forest ecosystems in the country; however, little is known regarding the biology of the fungus. The aim of this study was to develop markers to determine the mating types of individual isolates of R. quercus‐mongolicae collected across the country and then determine the mating‐type ratio in natural populations. To achieve this, partial sequences of MAT1‐1–3 and MAT1‐2–1 genes were amplified using degenerate primers and cloned. The new primer sets, which were specific to each mating‐type idiomorph, identified isolates as MAT1‐1 and MAT1‐2 mating types. The roughly equal frequencies of the two mating types suggest that sexual reproduction might have occurred in natural populations of R. quercus‐mongolicae in South Korea.

Estimating Flight Distance of Platypus koryoensis (Coleoptera: Curculionidae) by Mark-Release-Recapture and Its Validation by Field Observation.

Korean oak wilt (KOW) is vectored by the beetle Platypus koryoensis (Murayama) (Coleoptera: Curculionidae), a native species of Korea, whose dispersal distance is a key factor determining the spread of damage by KOW. To estimate dispersal distance at stand level, we conducted a mark-release-recapture (MRR) experiment and validated its results using an independent data. Sticky traps were attached to the trunks of oak trees up to 48.8 m from the release point. Beetles were marked with different three fluorescent powders by date and released, and the number of recaptured beetles was counted 90 min after release. To validate the flight distance, annual mean dispersal distance of P. koryoensis population was analyzed using GPS coordinates of oak trees with the symptom of KOW recorded in the field from 2012 to 2014 in independent oak stands that have been damaged by KOW since 2012. The beetles were recaptured only on the day they were released, suggesting that the beetles only make one flight. The percentage of recaptured beetles was 6.0 ± 1.6%. The mean dispersal distance was 18.0 ± 1.3 m, and more than 85% of recaptured beetles were caught within 25 m. Annual movement distances in infested stands were 24.1 and 19.9 m from 2012 to 2013 and 2013 to 2014, respectively, similar to the dispersal distance obtained from our MRR experiment. Our results showed that the dispersal distance of P. koryoensis estimated by MRR is a useful process for predicting the spread of areas damaged by KOW.

Draft Genome Sequence of the Fungus Associated with Oak Wilt Mortality in South Korea, Raffaelea quercus-mongolicae KACC44405.

ABSTRACTThe fungus Raffaelea quercus-mongolicae is the causal agent of Korean oak wilt, a disease associated with mass mortality of oak trees (e.g., Quercus spp.). The fungus is vectored and dispersed by the ambrosia beetle, Platypus koryoensis. Here, we present the 27.0-Mb draft genome sequence of R. quercus-mongolicae strain KACC44405.

Attractant effect of citral on Platypus koryoensis (Coleoptera: Curculionidae)

AbstractAn environmentally friendly control strategy for the ambrosia beetle Platypus koryoensis (Murayama), a vector of oak wilt disease, was investigated using the citral as a pheromone component. To develop an effective attractant trap, a semi‐field experiment (Yeoju) and a field experiment (Gunpo) were performed. Different ratios of four different attractant mixtures (ethanol 100 %, ethanol + citral (90:10, 95:5), ethanol + citral + hexane extract of Quercus mongolica (90:5:5)) were investigated to determine their effects on P. koryoensis. The 95:5 mixture of ethanol + citral had the greatest attractant effect on P. koryoensis. However, other ambrosia beetle species did not exhibit a specific response to citral. Our findings indicate that the pheromone citral was effective at attracting P. koryoensis and that certain concentrations of citral could be used to develop an effective and environmentally friendly control agent.

Attractant Effect of Trap Logs Treated with Ethanol to Platypus koryoensis (Coleoptera: Platypodidae)

The attractant effect to Platypus koryoensis (Murayama), an insect vector of Korean oak wilt disease, was determined using a multi-funnel trap and trap logs treated with ethanol and ethanol extract of the bark of the Mongolian oak Quercus mongolica (Fisher). The number of entrance holes in ethanol and bark ethanol extract treatments was higher than that in the control (blank bottle). However, the number of entrance holes in ethanol and bark ethanol extract treatments was not significantly different. The number of entrance holes in the logs increased with increase in diameter of the logs. The lower part of the trap logs had significantly more number of entrance holes than that in the upper part (p

Yeast Associated with the Ambrosia Beetle, Platypus koryoensis, the Pest of Oak Trees in Korea

Oak tree death caused by symbiosis of an ambrosia beetle, Platypus koryoensis, and an ophiostomatoid filamentous fungus, Raffaelea quercus-mongolicae, has been a nationwide problem in Korea since 2004. In this study, we surveyed the yeast species associated with P. koryoensis to better understand the diversity of fungal associates of the beetle pest. In 2009, a total of 195 yeast isolates were sampled from larvae and adult beetles (female and male) of P. koryoensis in Cheonan, Goyang, and Paju; 8 species were identified by based on their morphological, biochemical and molecular analyses. Meyerozyma guilliermondii and Candida kashinagacola were found to be the two dominant species. Among the 8 species, Candida homilentoma was a newly recorded yeast species in Korea, and thus, its mycological characteristics were described. The P. koryoensis symbiont R. quercus-mongolicae did not show extracelluar CM-cellulase, xylanase and avicelase activity that are responsible for degradation of wood structure; however, C. kashinagacola and M. guilliermondii did show the three extracellular enzymatic activities. Extracelluar CM-cellulase activity was also found in Ambrosiozyma sp., C. homilentoma, C. kashinagacola, and Candida sp. Extracelluar pectinase activity was detected in Ambrosiozyma sp., C. homilentoma, Candida sp., and M. guilliermondii. All the 8 yeast species displayed compatible relationships with R. quercus-mongolicae when they were co-cultivated on yeast extract-malt extract plates. Overall, our results demonstrated that P. koryoensis carries the yeast species as a symbiotic fungal associate. This is first report of yeast diversity associated with P. koryoensis.

Development of a mass trapping device for the ambrosia beetle, Platypus koryoensis, an insect vector of oak wilt disease in Korea

Oak wilt disease caused by a symbiotic fungus of ambrosia beetles is a serious problem in oak forest in Asian countries, with the potential to become a great threat to oak forests worldwide. In this study, we developed a control method, consisting of collection devices attached directly to infested host trees, for mass trapping of emerging ambrosia beetles. Effectiveness of the device was evaluated in terms of the retention fluid used in collection bottles, and the position of the bottles along the host trunk. A total of 87,081 ambrosia beetles were captured from 23 oak trees (Quercus mongolica). More beetles were captured in collection bottles installed at low positions of oak stems, compared to collection bottles located at the middle and upper positions (30, 90, 150cm above ground). We analyzed the effect of ethanol and water on beetle capture, determining that bottle position was more important than the contents of the collection bottle. There was no statistical difference between catches with ethanol vs water. There was a positive relationship between host DBH (diameter at breast height) and the number of captured beetles. Our mass trapping device proved to be very effective for capturing emerging ambrosia beetles from damaged oak trees in field tests. This new device could be useful in managing the population of ambrosia beetles, and has the potential to reduce the spread of oak wilt disease in oak forests.

Diurnal flight pattern of Platypus koryoensis (Coleoptera: Platypodinae) in relation to abiotic factors in Korea

The diurnal flight pattern of Platypus koryoensis (Murayama) was examined using sticky traps attached to the trunks of oak trees in central Korea in 2010 and 2011. The flight activities of the beetle were estimated on the basis of 3-h intervals for trap catches from 11:00 to 14:00 on the next day, on June 25–26 and July 1–2, 2010, and on the basis of 2-h intervals for trap catches from 5:00 to 17:00, between June 9 and July 21, 2011 (the peak flight period of the beetle). Over 77% of the beetles were caught from 9:00 to 13:00, with the daily variations in the facing slope. The beetles began to be caught when the air temperature reached around 16°C, and were the most active when the temperature ranged from 20 to 27°C. No beetles were caught during rainfall, suggesting that rainfall is one of the factors that hinder beetle flight. The beetles were caught by traps in the east-facing plot earlier than those in the south- and west-facing plots suggesting that the flight behavior of the beetle can be affected by the light. Direction of the beetle flight during the peak of daily flight (from 09:00 to 13:00) was downward along the slope.

A New Record of Candida kashinagacola (Synonym Ambrosiozyma kashinagacola) from Galleries of Platypus koryoensis, the Oak Wilt Disease Vector, in Korea

The ambrosia beetle, Platypus koryoensis, is an economically important pest affecting oak trees in Korea. Candida kashinagacola was isolated from galleries of the beetle in oak wood and identified by analyses of morphology, physiological properties, and nucleotide sequence of the large subunit ribosomal DNA. This is the first report on Candida species associated with oak wilt disease vectored by the ambrosia beetle, Platypus koryoensis, in Korea.

An empirical predictive model for the flight period of Platypus koryoensis (Coleoptera: Platypodinae)

Between 2007 and 2009, field studies were conducted in four Quercus mongolica Fischer ex Ledebour forests in Korea to develop an empirical degree-day model for the flight period of the ambrosia beetle, Platypus koryoensis (Murayama). The lower developmental threshold temperature was estimated using an iterative method based on field trap catches and temperatures. The pooled proportion of the total number of beetles found in the traps at the end of the experiment was plotted against the accumulated degree-days at selected baseline temperatures, and these plots were fitted by the Weibull function. The baseline temperature with the highest coefficient of determination was considered the lower developmental threshold temperature, and this was estimated to be 5.8 °C. The explanatory power of the model was 89 %. Moreover, the model accurately predicted the time distributions of P. koryoensis flights in 2011 and 2012 at one of the sites. The estimated median flight dates in 2011 and 2012 were 4 days earlier and 5 days later than the corresponding observed flight dates, respectively. The estimated median date of flight advanced progressively during 1970–2010 by a total of 9 days due to an increase in annual mean temperature.

Platypus koryoensisによるコナラの枯損被害 -発生3年目の経過-

Platypus koryoensisによるコナラの枯損被害 -発生3年目の経過-

훈증방제 처리한 참나무시들음병 감염목의 사상균 조사

한국에서 발병하는 참나무시들음병은 암브로시아 곤충인 Platypus koryoensis.에 의해 전반되는 Raffaelea quercus-mongolicae 균류에 의해 발생한다. 이 병의 전파를 방지하기 위해 참나무시들음병 감염목을 벌채 후 비닐막을 씌워 훈증하고 벌채장소에 3년 이상 방치시키고 있다. 본 연구는 이런 훈증처리된 감염목에 존재하는 균류에 대한 정보를 얻고자 수행하였다. 천안 태조산 지역 두 곳에서 훈증처리된 감염목을 채집하고 진균을 분리하여 99개 균주를 얻었다. 분리 균주를 형태적 특성과 translation elongation factor 1-alpha 유전자와 ITS rDNA region 염기서열에 의거한 분자적 방법으로 동정한 결과 Hypocrea, Trichoderma, Penicillium 속에 속하는 종들이 확인되었다. 이중 Trichoderma 속에 속하는 종이 주요 균류이었다. 조사결과 병원균인 R. quercus-mongolicae와 매개충인 P. koryoensis는 검출되지 않았다. 본 연구결과는 훈증 처리한 참나무시들음병 감염목이 3년 이상 되면 더 이상의 피해를 유발할 위험요소가 없다는 과학적 증거를 제시한다. Korean oak wilt disease caused by Raffaelea quercus-mongolicae is vectored by the ambrosia beetle Platypus koryoensis. To prevent the spread of the disease, the beetle infested oak tree had been cut into logs, covered with plastic vinyl, fumigated with a pesticide, and stored for three years on the site where the tree was cut. This study was carried out to get information on the fungi colonizing the fumigated oak wood. Wood disk samples collected from the fumigated oak logs at two locations in the Taejo Mountain, Cheonan city, were used for fungal isolation. A total of 99 filamentous fungal isolates were obtained from the wood disk samples. Hypocrea spp., Trichoderma spp. and Penicillium spp. were identified based on morphological characteristics and nucleotide sequence analysis of translation elongation factor 1-alpha gene and ITS rDNA region. Trichoderma was the major fungal group. R. quercus-mongolicae, and P. koryoensis were not detected from the fumigated oak wood. Our work provided evidence that after three years of storage, the fumigated oak wilt-diseased logs should be no longer harmful source of oak wilt disease transmission.

Density related plasticity in stand‐level spatial distribution of the ambrosia beetle, Platypus koryoensis (Coleoptera: Curculionidae)

AbstractWe tested the hypothesis that the population density of ambrosia beetles at the stand level influences the spatial distribution of infested trees. We evaluated the spatial distribution of the ambrosia beetle, Platypus koryoensis (Murayama) in three oak forest stands that varied in beetle population density using a multi‐year trapping survey. We used these data to inform a clustering analysis based on aggregation indices using the SADIE software. Four important findings emerged: (1) the spatial distribution pattern of P. koryoensis at the stand level changed as the population density of the beetle varied; (2) at low population densities, beetle distribution was contagious at the stand level; (3) as beetle population densities increased, the spatial distribution of infested trees became random, potentially due to beetle avoidance of mass attacked trees; and (4) at high beetle population densities, the spatial distribution of infested trees became contagious, possibly due to temporal changes in location of the attack epicenter within the stand. Our results support the hypothesis that beetle population density has consequences for the spatial distribution of infested trees at the within‐stand scale. We conclude that the spatial distribution of infested trees is flexible in response to beetle population density, suggesting that beetle attack behaviors are mediated by one or more density‐dependent effects.

졸참나무와 서어나무 고사목의 나무좀의 다양성과 풍부도

This study was conducted to elucidate the patterns of occurrence of bark beetles on deadwoods of Quercus serrata Fisher and Carpinus laxiflora Blume which are expected to increase due to climate change. The survey was carried out at the LTER site in Gwangneung forest in Gyeonggi Province in 2007-2008. Bark beetles were collected using emergence traps and attraction traps (funnel trap and window trap). A total of 408 beetles belonging to 12 species in two subfamilies were collected. Platypus koryoensis (Murayama) was the most abundant species. P. koryoensis and Xylosandrus germanus (Blandford) occurred mainly in deadwoods of Q. serrata. All other species, except two rare species, occurred commonly in deadwood of both tree species. Species richness and abundance of bark beetles were higher in the attraction traps than in the emergence traps, and higher in Q. serrata than in C. laxiflora. These indexes were higher in classes I-II or I-III than in classes III-IV or IV of deadwood. Bark beetle communities differed according to years and showed a little difference between tree species.

Attack Pattern of Platypus koryoensis (Coleoptera: Curculionidae: Platypodinae) in Relation to Crown Dieback of Mongolian Oak in Korea

The ambrosia beetle, Platypus koryoensis (Murayama), vectors the Korean oak wilt (KOW) pathogen, Raffaelea quercus-mongolicae K.H. Kim, Y.J. Choi, & H.D. Shin, in Korea, which is highly lethal to Mongolian oak, Quercus mongolica Fisch., and is considered a major threat to forest ecosystem health. We characterized the attack pattern of P. koryoensis along the lower trunk of 240 Mongolian oaks in relation to tree decline symptoms on Mt. Uam in Gyeonggi-Do Province, Korea during June-July 2009. For each tree, we recorded diameter at breast height (dbh) (DBH) and P. koryoensis entrance hole density at two heights along the lower trunk (near groundline and at 1.5 m above groundline) and on opposite sides (downslope side and upslope side). Trees were assigned to one of three dieback classes: 1) apparently healthy, no or practically no wilted foliage, and no obvious platypodine frass near the base of the tree; 2) no or only partial wilting with obvious frass near the base of the tree; and 3) apparently recently killed by KOW with all foliage wilted and mostly retained with obvious frass near the base of the tree. As dieback class increased from 1 to 3, P. koryoensis entrance hole density increased at all four trunk locations. Attack density was highest on the downslope side of the trunk near groundline, and principal component analysis indicated that this trunk location was the best indicator of tree dieback. In addition, DBH tended to increase with dieback class suggesting that larger trees were infested first.

Filamentous Fungi Isolated from Platypus koryoensis, the Insect Vector of Oak Wilt Disease in Korea

The ambrosia beetle, Platypus koryoensis, is a serious pest of oak trees in Korea. In this study we investigated filamentous fungi present in the body of the beetle. Fourteen genera of filamentous fungi belonging to Ascomycota and Basidiomycota were isolated. Among the isolated fungi, some were able to produce wood degrading enzymes. This is first report of fungi associated with P. koryoensis.

Microstructure of the prothoracic mycangia in the ambrosia beetle Platypus koryoensis (Coleoptera: Curculionidae: Platypodinae)

Platypus koryoensis (Murayama) (Coleoptera: Curculionidae: Platypodinae) is a minute ambrosia beetle that can cause significant damage to live oak trees ( Quercus mongolica) along with its symbiotic pathogenic fungus ( Raffaelea sp.). Although both sexes of the beetle have a number of cuticular depressions for carrying microorganisms, only the females have mycangia that are typical in size on the pronotum. The mycangial cavities are filled with a mass of amorphous substances including yeast-like spores. In addition, mycangial cavities are equipped with cuticular pores which release substances to support symbiotic microorganisms during storage. Small depressions of both sexes can be subdivided into two clusters according to their relative sizes and locations. Although they have a typical cuticular peg (basiconic sensillum), they also share a common morphological characteristic with the typical mycangium of female: a round outlet and an invaginated reservoir containing a mass of secretory substances. Accordingly, our fine structural data suggest that both the female mycangia and the clusters of small cuticular depressions in both sexes also have a mycangial function in common regardless of their relative size and location.

은 나노 용액을 활용한 참나무 시들음병 방제 연구

본 연구는 세계적으로 참나무류 집단고사를 일으켜 문제가 되고 있는 R. quercivorus 균의 방제를 위한 연구로 최근 나노기술을 활용하여 참나무시들음병(Oak wilt)의 원인균인 R. quercivorus를 방제하고 매개충인 광릉긴나무좀(Platypus koryoensis)의 생태 및 형태연구에 관한 것이다. Nano-silver 용액 WA-AT-WB13R을 이용하여 R. quercivorus 균에 대한 in vitro 실험을 실시하였으며, WAAT-WB13R 용액이 100 ppm에서 균사 및 포자의 생장 억제 효과가 있음을 확인하였다. 각각 10, 30, 50, 100 ppm 처리하여 SEM 관찰 결과, 무처리구에서는 균사의 형태가 정상적임을 확인하였고 30 ppm에서부터 균사의 형태가 조금씩 변형이 일어나다가 100 ppm에서는 균사 및 포자가 비정상적으로 일그러져 있는 것을 확인하였다. 또한 매개충인 P. koryoensis의 충체에 붙어있는 균사와 포자를 SEM을 이용하여 위와 같은 방법으로 처리 관찰 결과, 표면과 균낭의 균사 및 포자의 형태가 100 ppm에 가까울수록 형태적인 변화를 관찰할 수 있었다. 기내에서의 R. quercivorus의 균사 생장억제효과를 바탕으로 수간주사(Trunk injection)를 실시한 결과, 철원과 홍천에서는 시들음 및 약해 증상을 확인할 수 없었다. 또한 춘천은 7월 시들음 증상을 보였으나 그 후 시들음 증상 및 약해를 보이지 않았다. 본 연구를 통하여 nano-silver 용액을 이용한 참나무시들음병의 원인균인 R. quercivorus의 생장억제 효과를 확인하였으며, nano-silver를 이용한 R. quercivorus 방제할 수 있음을 확인하였다. In other previous in vitro tests, the hyphal growth of Raffaelea quercivorus was inhibited by the treatments of various concentration of nano-silver. In this field tests, treatment of different concentrations of nano-silver to oak trees in Cheolwon and Hongcheon sites showed the inhibition effects against wilt disease caused by Raffaelea quercivorus. However, nano-silver-treated oak tree in Chuncheon site showed mild wilt symptoms with no phytotoxicity. Scanning electron microscope (SEM) observation confirmed that the spore and hypha of Raffaelea sp. inside the vessels were damaged by nano-silver. This result indicates the application of nanosilver is effective for control of Raffaelea quercivorus in the field.