Discrimination among host tree species by the ambrosia beetle Platypus quercivorus

The ambrosia beetle Platypus quercivorus is a vector for the fungus that causes Japanese oak wilt, and susceptibility to infestation by P. quercivorus varies by tree species. We postulated that P. quercivorus discriminates among host tree species differing in susceptibility to attack. To test this postulate, we counted the number of flying male beetles (NFM), the number of holes bored by male beetles (NH), and the number of flying female beetles (NFF) per unit area of bark surface in three fagaceous tree species: Quercus crispula (with high susceptibility to infestation) and Q. serrata and Castanea crenata (both with low susceptibility). NFM and NH were used to calculate the proportion of male beetles that bored holes out of those that flew to the tree (PBM). We used generalized additive models to predict NFM, NFF, and PBM. The locations of trees, expressed as x and y coordinates, numbers of weeks after the first male beetle’s flying (WEEK), diameters of trees 130 cm above ground (DBH), and tree species (SP) were incorporated into the models as candidate explanatory variables. The best-fit models for NFM and NFF included WEEK and DBH and the effect of location; SP was not included in the models. For PBM, the best-fit model included WEEK, DBH, and SP. The results indicate that male P. quercivorus prefer Q. crispula to Q. serrata and C. crenata and that selection is made before boring holes on trees, but that P. quercivorus do not discriminate among host species when they fly to trees.     

Aggregation ofPlatypus quercivorus (Murayama) (Coleoptera: Platypodidae) on oak logs bored by males of the species

To provide evidence for the aggregation ofPlatypus quercivorus (Murayama) (Coleoptera: Platypodidae) in association with the mass mortality of oak trees in Japan, we compared the number of beetles attracted to oak logs bored by males with the number of beetles attracted to logs that had not been bored. Large numbers of males and females were attracted to the bored logs, and the total numbers increased as the number of entry holes in the logs increased. This result shows that both male and female beetles aggregate on logs bored by the males. We collected a large number of beetles attracted to living trees bored by the beetles, and the total number of beetles collected increased as the number of entry holes/m² on the tree trunk increased. Beetles also aggregated on living trees bored by the males.     

Types of frass produced by the ambrosia beetle <Emphasis Type="Italic">Platypus quercivorus</Emphasis> during gallery construction,and host suitability of five tree species for the beetle

We studied the biology of the ambrosia beetle Platypus quercivorus in the logs of five tree species to determine: (1) the relationship between the amount of frass produced by beetles and tunnel length, (2) the relationship between frass shape and the morphological characteristics of P. quercivorus mouthparts, and (3) the suitability of five tree species for P. quercivorus reproduction. Five logs each from healthy Quercus crispula, Q. serrata, Castanea crenata, Sorbus japonica, and Cryptomeria japonica trees were used in this experiment. The results showed that there was a linear relationship between the amount of frass and tunnel length. Whenever powdery frass was produced, larvae were found in the gallery in the log, while fibrous frass was present only in galleries that contained just adults. The mouthparts of adults were completely sclerotized, which likely accounts for the fibrous frass production. Host preference of P. quercivorus was examined at two stages using five tree species. The first stage is digging initiation, which concerns male preference for digging a tunnel. More holes were made by males on S. japonica and Q. serrata logs, while fewer holes were made on C. japonica logs. The second stage is characterized by female orientation, mating, and progeny development. Platypus quercivorus could complete its lifecycle only in the two Quercus spp.     

Relationships between mass mortality of two oak species (Quercus mongolica Turcz. var.grosseserrata Rehd. et Wils. andQ. serrata Thunb.) and infestation by and reproduction ofPlatypus quercivorus (Murayama) (coleoptera: Platypodidae)

This study investigated the number of adults ofPlatypus quercivorus (Murayama) captured on host oak (Quercus spp.) trees, the attack density (the number of entry holes per 100 cm²), and the number of emerging adults to clarify the relationships between the beetle’s colonization on trees in oak stands and tree mortality. The initial attack ofP. quercivorus, which was the most intense attack, was observed on most living trees simultaneously. Although some attacked trees died within the year of the attack or in the next year, a high density of attack did not usually cause the death of host trees. Surviving trees suffered low levels of consecutive attack after the initial attack. BecauseP. quercivorus successfully produced broods only in the dead trees, the population of the insect seems to be maintained only in stands where oak mortality occurs. However, the adults that landed on most of the surviving trees appeared unable to reproduce probably due to degradation of host quality. Thus, oak mortality probably ceases within 3 or 4 years after the start of infestation in a stand, with subsequent reductions in population density of the borer.     

Spatial distribution pattern of attack of the oak borer,Platypus quercivorus (Murayama) (Coleoptera: Platypodidae), and scolytid ambrosia beetles (Coleoptera: Scolytidae) on fresh logs

The spatial distribution patterns of the attack on fresh logs ofPasania edulis was studied for the oak borer,Platypus quercivorus (Murayama), and two species of Scolytid ambrosia beetles,Xylosandrus crassiusculus (Motschulsky) andXyleborus attenuatus Blanford, in 1994 and 1995. On the logs where onlyP. quercivorus attacked, the entry holes were distributed uniformly when attack intensity was low. However, the distribution pattern became more aggregated with the increase in attack intensity. On logs where bothP. quercivorus and the two Scolytid species attacked, there was a negative association between the spatial distribution of the entry holes ofP. quercivorus and that of scolytids. Simultaneous attack of two scolytids also increased the degree of aggregation of the entry holes ofP. quercivorus. The entry holes of scolytids were distributed in groups irrespective of the attack intensity of scolytids andP. quercivorus. These results suggest an asymmetrical interspecific relationship betweenP. quercivorus and scolytids. Concentration of the entry holes ofP. quercivorus in a small area may cause a considerable decline in the reproductive success in the galleries constructed there.     

Population dynamics of <Emphasis Type="Italic">Monochamus galloprovincialis</Emphasis> Olivier (Coleoptera: Cerambycidae) in two pine species under laboratory conditions

The study of the life history dynamics of the pine sawyer beetle Monochamus galloprovincialis (Olivier) is important because the beetles vector the pinewood nematode. The objectives of this study were to investigate differences in beetle life history parameters between the two common host tree species in Turkey, Pinus sylvestris and Pinus nigra. Relationships between the number of oviposition sites, holding time (time between log cut and oviposition), log moisture content, log volume and area, and adult survivorship were evaluated. No significant differences were found between the two tree species except adult density per m². The holding time did not influence the number of oviposition sites, larval entry holes or adults for P. sylvestris. There was a negative correlation between the holding time and the number of oviposition sites for P. nigra. The number of adults emerged per log was correlated with the number of larval entry holes only for P. sylvestris. Only 12 and 15% of the initial cohort completed development and emerged as adults for P. sylvestris and P. nigra, respectively. Both tree species are equally suitable hosts for M. galloprovincialis development. We conclude that the high within-log mortality of beetles is a combination of resource quality and quantity factors and intraspecific competition and cannibalism during larval development.     

Changes in water status in seedlings of six species in the Fagaceae after inoculation with Raffaelea quercivora Kubono et Shin-Ito

To clarify the differences in susceptibility of six species in the Fagaceae (Quercus crispula, Quercus serrata, Quercus acutissima, Quercus phillyraeoides, Quercus glauca, and Castanopsis cuspidata var. sieboldii) to Raffaelea quercivora, we inoculated this fungus on seven potted 5-year-old seedlings of each species, observed symptom development, and measured xylem pressure potential (XPP) after inoculation. The first death was observed on the 11th day in Q. crispula and on the 56th day in Q. serrata. The number of dead seedlings of Q. crispula and Q. serrata were five and one, respectively, whereas no mortality was observed in the other four species. The XPP of inoculated seedlings in both Q. crispula and Q. serrata decreased after inoculation. In contrast, the XPP of inoculated seedlings of the other four species remained almost the same as in the control seedlings. These results indicate that R. quercivora is pathogenic to Q. crispula and Q. serrata and that the susceptibility of the six Fagaceae species in our study differed among species.     

Effects of mating on the termination of aggregation by the oak borer,Platypus quercivorus (Murayama) (Curculionidae: Platypodinae) during host colonization

We conducted a field experiment to determine whether logs bored by male Platypus quercivorus beetle were less attractive to conspecifics after beetles had mated. Bored (with male beetles) and unbored logs were placed in a beetle-infested forest and enclosed within a cage. For half of the bored logs, female beetles were released to mate with the male beetles. Log attractiveness was determined by assessing the number of beetles captured on adhesive paper placed on each cage enclosing the log. On the logs on which female beetles were released, the number of beetles captured decreased distinctly after release, and did not differ from the number captured on the unbored logs. In contrast, the number of beetles captured on logs with only unpaired males was higher than the number captured on the unbored logs. This result confirms that the attractiveness of logs bored by male P. quercivorus beetles declines after mating occurs. To our knowledge, this is the first evidence for the relaxation of aggregation pheromone following mating for beetles in the subfamily Platypodinae.     

Responses ofQuercus sapwood to infection with the pathogenic fungus of a new wilt disease vectored by the ambrosia beetlePlatypus quercivorus

Quercus serrata andQ. crispula wilt during the summer in wide areas along the Sea of Japan. Mass attacks of trees by an ambrosia beetle (Platypus quercivorus) are characteristic before appearance of the wilting symptoms. This study investigated the pathogenic effects of a fungus detected specifically in the wilting trees. This hyphomycete fungus,Raffaelea sp., has a distribution that correlates with the discolored xylem area called wound heartwood in which vessels are dysfunctional. Tylosis formation around the hyphae indicates vessel dysfunction. In areas with discoloration, the fungal hyphae were invading living ray parenchyma cells from the vessel lumen. As a protective reaction the ray cells exuded yellow substances into the vessels, but these substances seemed ineffective against the fungal activity, probably because the fungus disperses along the beetle's gallery before enough substance can accumulate. It should allow wide discoloration in sapwood. Cambium was not necrotic around the fungus. The cytological process in the host was as follows: (1) synthesis of secondary metabolites by the stimuli of oak fungus; (2) exudation of yellow substances into vessels; and (3) dysfunction of vessels and wound heartwood formation. In regard to wilting of trees, the pathogenicity of the fungus should be assessed by its ability to stop sap flow.     

Relative dominance of the mold fungus,<Emphasis Type="Italic">Raffaelea</Emphasis> sp., in the mycangium and proventriculus in relation to adult stages of the oak platypodid beetle,<Emphasis Type="Italic">Platypus quercivorus</Emphasis> (Coleoptera; Platypodidae)

Microorganisms associated with the oak platypodid beetle,Platypus quercivorus (Murayama), were isolated from the mycangium of adult females, from the proventriculus of adults of both sexes, and from galleries in the period before dispersal. Fungi isolated from female mycangia were separated into three groups:Raffaelea sp., yeasts (mainlyCandida spp.), and other species.Raffaelea sp. was isolated predominantly from the teneral stage to the dispersal stage, but was not isolated from the mycangia of mother beetles in new galleries. Yeasts were isolated in every beetle stage tested and their isolation rate was over 80% from the teneral stage to the dispersal stage. All three fungal groups were found in the female proventriculus.Raffaelea sp. was isolated only in the dispersal stage at a rate of 40%, whereas the isolation rate of yeasts gradually increased beginning in the mature stage and reached 100% in the rearing stage. In contrast, in the male proventriculus, onlyRaffaelea sp. and yeasts were isolated in the dispersal and rearing stages. The isolation rate in the rearing stage ofRaffaelea sp. was less than 20%, but that of yeasts was 100%, although these rates were almost the same in the dispersal stage.Raffaelea sp. and yeasts were also isolated from cradles containing eclosing pupae. These results suggest thatP. quercivorus acquiresRaffaelea sp. and yeasts in their mycangia from the cradles immediately after eclosion, and maintain them to the dispersal stage. Then, they transmit these fungi from old to new galleries by way of mycangia, and possibly the digestive system.     

Manipulation of tannins in oaks by galling cynipids

We measured the protein precipitation capacity of tannins in the tissues of Quercus crispula and Quercus serrata galls induced by a cynipid (Trigonaspis sp.) to examine the nutrition hypothesis on gall induction. The protein precipitation capacity was significantly lower in the nutritive tissues of galls, on which the cynipids feed, than in ungalled sound leaves and in the outer gall tissues. In addition, the protein precipitation capacities in the leaves and in the outer gall tissues were significantly larger in Q. crispula than in Q. serrata samples, whereas that of the nutritive tissues did not differ between these oak species. These results suggest that gall induction is one of the adaptations of galling cynipids to host–plant defensive compounds, and support the nutrition hypothesis.     

Stand structure and composition of a 60-year-old larch (Larix kaempferi) plantation with retained hardwoods

Tree retention is understood as a key practice in creating complexity, leading to heterogeneity in resources and habitats in managed stands. In this article, we clarify the long-term effects of tree retention on stand structure and tree-species composition in a 60-year-old Larix kaempferi plantation in central Japan. In our study plot (1.5 ha) there were 18 stems/ha of retained trees (determined by tree-ring analysis), mostly Quercus crispula. We conducted spatial analyses and tested the hypothesis that tree abundance, size structure, and species composition and diversity change with distance from the retained trees. Near the retained trees, L. kaempferi showed a reduction of 40%–60% in basal area, due presumably to the shading effect. In contrast, the nearby area showed greater species diversity in the canopy layer. The retained trees created patches of different species composition in the understory. The spatial gradient of shade and colonization opportunity provided by retained trees greatly affect the distribution of the colonized species, according to their shade tolerance and seed-dispersal ability, which resulted in the stand structure with a heterogeneous shrub-layer vegetation. Retention proved particularly important for the enhancement and long-term maintenance of structural and compositional complexity in L. kaempferi plantations.     

<Emphasis Type="Italic">Ophiostoma</Emphasis> species associated with bark beetles infesting three <Emphasis Type="Italic">Abies</Emphasis> species in Nikko,Japan

Ophiostoma species were isolated from bark beetles and Abies mariesii, A. veitchii and A. homolepis attacked by the beetles in Nikko, Tochigi, central Honshu, Japan. One to two Ophiostoma species were frequently isolated from each species of bark beetle. Ophiostoma subalpinum was the most common associate of Cryphalus montanus. Ophiostoma sp. B as well as O. subalpinum was a common fungus associated with Polygraphus proximus. Ophiostoma europhioides was isolated from Dryocoetes hectographus and D. autographus as one of the common associates. Ophiostoma sp. J and Ophiostoma sp. S were frequently isolated from D. autographus and D. striatus, respectively. These fungi seem to have specific relationships with particular bark beetles. Ophiostoma sp. B, Ophiostoma sp. J and Ophiostoma sp. S have unique morphological characteristics and appear to be new species. Five trees of A. veitchii, approximately 43 years old, were inoculated with five Ophiostoma species to assess the relative virulence of the fungi. Ophiostoma subalpinum, Ophiostoma sp. B, and O. europhioides had relatively higher virulence than the other species studied.     

Ophiostomatoid fungi associated with bark beetles onAbies veitchii in wave-regenerated forests

Relationships between tree mortality and bark beetle infestation onAbies veitchii at the wave-regenerated forest in Mt. Asahi, Okuchichibu area were investigated. Most of the firs with green needles and newly developed current year’s shoots in the dieback zone were heavily infested by bark beetles before the death of the trees. After heavy infestation of beetles, about half of the infested firs died within the year, and the other half died in the next year. When the species composition of bark beetles and associated ophiostomatoid fungi were investigated in Mt. Asahi and also at a typical wave-regenerated forest in Mt. Shimagare, Yatsugatake area,Cryphalus montanus andC. piceae were dominant beetle species for Mt. Asahi and Mt. Shimagare, respectively.Ophiostoma subalpinum andO. europhioides were dominant fungal species at both wave-generated forests. BecauseO. subalpinum was detected more frequently from deeper areas of sapwood thanO. europhioides, it was suggested that the fungal species may accelerate the death of stressed firs in wave-regenerated forests. Contribution No. 169, Laboratory of Plant Parasitic Mycology, Institute of Agriculture and Forestry, University of Tsukuba.     

Inducing infection of oak logs by a pathogenic fungus carried byPlatypus quercivorus (Murayama) (Coleoptera: Platypodidae)

This study examined the frequency of infection by an unidentified pathogenic fungus of oak logs bored into by males alone or by both males and females ofPlatypus quercivorus (Murayama) in the field. The fungus, which is associated with mass mortality of oak trees in Japan, was not isolated from logs bored into by males alone, which bored only short entrance galleries. However, it was isolated from logs bored into by both males and females, which together bored longer galleries and reproduced successfully. This suggests that it is difficult for the fungus to colonize logs bored into by males alone. The fungus was not isolated from a log in which the beetles failed to reproduce, and in which the galleries were significantly shorter than in logs where reproduction succeeded, but it was unclear whether the shortness of the galleries prevented colonization of the log by the fungus. The study also revealed that some gallery-initiating males survived for at least 2 months in the absence of females, and that females elongated entrance galleries that had been bored by the gallery-initiating males.     

Differences in leafminer (Phyllonorycter, Gracillariidae, Lepidoptera) and aphid (Tuberculatus, Aphididae, Hemiptera) composition among Quercusdentata, Q. crispula, Q. serrata, and their hybrids

Leafminer (Phyllonorycter, Gracillariidae, Lepidoptera) and aphid (Tuberculatus, Aphididae, Hemiptera) composition were studied in three deciduous oak species, Quercus dentata, Q. crispula, and Q. serrata, and their hybrids in Tomakomai Experimental Forest of Hokkaido University, Hokkaido, northern Japan. Identification of trees in this forest was done mainly on the basis of discriminant analysis on leaf morphology with reference to trees in pure Q. dentata and Q. crispula stands and a Q. serrata stand mixed with Q. crispula. The results suggested that hybridization occurred in all combinations (i.e. Q. dentata–Q. crispula, Q. crispula–Q. serrata, and Q. serrata–Q. dentata) and the frequency of hybrids was approximately 10%. The composition of Phyllonorycter and Tuberculatus species differed between Q. dentata and Q. crispula or Q. serrata, but did not differ between Q. crispula and Q. serrata. Thus, Q. dentata could differ from Q. crispula and Q. serrata in chemical properties that determine herbivore host selection, survival, and performance, possibly reflecting eco-physiological differences or phylogenetic distances. The study insects were divided into three groups: species specialized to Q. dentata (three Phyllonorycter and one Tuberculatus species), those to Q. crispula and Q. serrata (six Phyllonorycter and two Tuberculatus species), and a species collected at least from Q. dentata and Q. crispula (one Tuberculatus species). Putative hybrid trees of Q. dentata and Q. crispula harbored both Q. dentata-specific and Q. crispula-specific insects.     

Extent of colonization by Raffaelea quercivora of artificially inoculated living and gamma‐ray‐sterilized seedlings of two Japanese and three American oak species

Mass mortality of Fagacean tree species caused by Raffaelea quercivora has occurred widely in Japan. Because conidia or other propagules of the pathogen have not been found in infected trees, pathogen spread is assumed to occur primarily by hyphae. To clarify the relationship between hyphal growth of the pathogen within trees and their vessel arrangements, we examined two native Japanese oaks, Quercus crispula and Quercus glauca, and three exotic American oaks, Quercus coccinea, Quercus palustris and Quercus rubra. Quercus glauca is a radial‐porous species, whereas the other four species have a ring‐porous wood structure. Hyphal growth within inoculated potted living seedlings and in cut, sterilized stem segments of these species was examined microscopically after fungal inoculation. Water conductance in the seedlings was examined using transverse stem sections. The proportion of non‐conductive sapwood in Q. crispula, Q. coccinea and Q. palustris differed between inoculation and control treatment, being much higher in inoculated seedlings. The proportions were positively correlated with the extent of the hyphal growth. In sterilized stem segments, the extent of fungal colonization varied among the foreign ring‐porous species Q. coccinea, Q. palustris and Q. rubra. It is hypothesized that the extent of colonization by R. quercivora reflects the extent of non‐conductive sapwood irrespective of tree species, but is little affected by vessel arrangements.     

Predisposition to bark beetle attack by root herbivores and associated pathogens: Roles in forest decline,gap formation,and persistence of endemic bark beetle populations

Bark beetles are largely known for their ability to undergo intermittent population eruptions that transform entire landscapes and pose significant economic hardships. However, most species do not undergo outbreaks, and eruptive species usually exert only minor disturbances. Understanding the dynamics of tree-killing noneruptive species can provide insights into how beetles persist at low densities, and how some spatiotemporal patterns of host predisposition may more likely favor breaching eruptive thresholds than others. Elucidating mechanisms behind low-density populations is challenging, however, due to the requirement of long-term monitoring and high degrees of spatial and temporal covariance. We censused more than 2700 trees annually over 7 years, and at the end of 17 years, in a mature red pine plantation. Trees were measured for the presence of bark beetles and wood borers that breed within the primary stem, root weevils that breed in root collars, and bark beetles that breed in basal stems. We quantify the sequence of events that drive this decline syndrome, with the primary emergent pattern being an interaction between below- and above-ground herbivores and their fungal symbionts. This interaction results in an expanding forest gap, with subsequent colonization by early-successional vegetation. Spatial position strongly affects the likelihood of tree mortality. A red pine is initially very likely to avoid attack by tree-killing Ips beetles, but attack becomes increasingly likely as the belowground complex spreads to neighboring trees and eventually make trees susceptible. This system is largely internally driven, as there are strong gap edge, but not stand-edge, effects. Additional stressors, such as drought, can provide an intermittent source of susceptible trees to Ips beetles, and elevated temperature slightly accentuates this effect. New gaps can arise from such trees as they subsequently become epicenters for the full complex of organisms associated with this decline, but this is not common. As Ips populations rise, there is some element of positive feedback, in that the proportion of killed trees that were not first colonized by root organisms increases. This positive feedback is very weak, however, and we propose the slope between beetle population density and reliance on host stress as a quantitative distinction along a gradient from noneruptive through eruptive species. Almost all trees colonized by Ips were subsequently colonized by wood borers, likely a source of negative feedback. We discuss implications to our overall understanding of cross-scale interactions, between-guild interactions, forest declines, and eruptive thresholds.     

Response of bark beetles and their natural enemies to fire and fire surrogate treatments in mixed-conifer forests in western Montana

Four treatments (control, burn-only, thin-only, and thin-and-burn) were evaluated for their effects on bark beetle-caused mortality in both the short-term (one to four years) and the long-term (seven years) in mixed-conifer forests in western Montana, USA. In addition to assessing bark beetle responses to these treatments, we also measured natural enemy landing rates and resin flow of ponderosa pine (Pinus ponderosa) the season fire treatments were implemented. All bark beetles were present at low population levels (non-outbreak) for the duration of the study. Post-treatment mortality of trees due to bark beetles was lowest in the thin-only and control units and highest in the units receiving burns. Three tree-killing bark beetle species responded positively to fire treatments: Douglas-fir beetle (Dendroctonus pseudotsugae), pine engraver (Ips pini), and western pine beetle (Dendroctonus brevicomis). Red turpentine beetle (Dendroctonus valens) responded positively to fire treatments, but never caused mortality. Three fire damage variables tested (height of crown scorch, percent circumference of the tree bole scorched, or degree of ground char) were significant factors in predicting beetle attack on trees. Douglas-fir beetle and pine engraver responded rapidly to increased availability of resources (fire-damaged trees); however, successful attacks dropped rapidly once these resources were depleted. Movement to green trees by pine engraver was not observed in plots receiving fire treatments, or in thinned plots where slash supported substantial reproduction by this beetle. The fourth tree-killing beetle present at the site, the mountain pine beetle, did not exhibit responses to any treatment. Natural enemies generally arrived at trees the same time as host bark beetles. However, the landing rates of only one, Medetera spp., was affected by treatment. This predator responded positively to thinning treatments. This insect was present in very high numbers indicating a regulatory effect on beetles, at least in the short-term, in thinned stands. Resin flow decreased from June to August. However, resin flow was significantly higher in trees in August than in June in fire treatments. Increased flow in burned trees later in the season did not affect beetle attack success. Overall, responses by beetles to treatments were short-term and limited to fire-damaged trees. Expansions into green trees did not occur. This lack of spread was likely due to a combination of high tree vigor in residual stands and low background populations of bark beetles.     

Genotype distribution of Raffaelea quercivora in the oak galleries and its composition in the mycangia of Platypus quercivorus

Raffaelea quercivora is the pathogenic fungus that causes Japanese oak wilt. The female monogynous ambrosia beetle, Platypus quercivorus, carries this fungus in mycangia on the pronotum. These beetles bore galleries in oak trees with their partners to produce offspring, and they deposit fungus on the gallery walls from their mycangia. The offspring mature in the gallery, before loading the fungal pathogen and flying from the gallery to other healthy trees. To investigate the unloading and loading modes of the fungus within the gallery, we developed four polymorphic microsatellite markers for R. quercivora and identified the fungal genotypes in the galleries and mycangia of the beetles. Small wood chips were sampled at 5–10‐mm intervals from the walls of five galleries in a dead Quercus serrata tree. The pronota were also sampled from five female adult beetles. The genotypes of the R. quercivora isolates from the wood chips and pronota were identified using the microsatellite makers. The genotypic analysis showed that each gallery was inhabited patchily by 5–10 genotypes of R. quercivora, and the mycangia of each beetle contained 3–6 genotypes. These results indicate that diverse R. quercivora genotypes are unloaded repeatedly from the mycangia of female beetles onto the gallery wall, which results in their patchy distribution on the walls. When the offspring leave the host tree, the fungal clones that proliferate in the walls are also loaded repeatedly into the mycangia of the mature beetles.