Platypus quercivorus ambrosia beetles use leaf volatiles in host selection

Although chemical volatiles emitted from host and non-host trees have been suggested as important cues for bark and ambrosia beetles, their responses to leaf volatiles is poorly understood. The oak ambrosia beetle, Platypus quercivorus (Murayama) (Coleoptera: Curculionidae), is a vector for the fungus that causes Japanese oak wilt. Using a Y-tube olfactometer, we tested the behavioral response of P. quercivorus to leaf volatiles emitted from four host trees – Quercus crispula Blume, Quercus serrata Murray, Quercus salicina Blume, and Castanea crenata Sieb. & Zucc. (all Fagaceae) – and two non-host trees, Fagus crenata Blume (Fagaceae) and Cryptomeria japonica D. Don (Cupressaceae). A flight mill was used to evaluate the effect of flight on the behavioral response to leaf volatiles. The bioassays were repeated 10× before and 10× after flight in the flight mill for each of the 54 individual beetles. Leaf volatile components were analyzed using gas chromatography–mass spectrometry. The bioassay results supported our hypothesis: P. quercivorus was attracted by the leaf volatiles of hosts and was deterred by the leaf volatiles of non-hosts. The behavioral response of P. quercivorus to the leaf volatiles was stronger after flight. Males had a stronger behavioral response than females to leaf volatiles. The leaf volatile chemical profile of the non-host C. japonica differed from the profile of the host plants. However, the chemical profile of the non-host F. crenata was similar to the profile of the hosts. Our findings provide insight into the functions of leaf chemical volatiles in the interaction of P. quercivorus with its hosts and non-hosts and may help improve the control of P. quercivorus and Japanese oak wilt.     

Effects of leaf conditions and flight activity on the behaviour of Platypus quercivorus (Murayama) (Coleoptera: Platypodidae)

The important role of semiochemicals in the interactions between plants and insects has been extensively investigated. The volatiles produced by oak trees are thought to attract the ambrosia beetle Platypus quercivorus (Murayama), which causes wilt disease in Quercus trees, resulting in widespread damage. In the present study, we hypothesized that (a) P. quercivorus is attracted to the leaf volatiles emitted by host trees and (b) the response of P. quercivorus to leaf volatiles is affected by flight. An experiment was performed to survey the preferences of both sexes of P. quercivorus for the leaf volatiles of Quercus crispula Blume at various stages of leaf deterioration, represented by different number of days after cutting. Additionally, the effect of flight on both sexes was evaluated by testing the beetle flight on a flight mill. The results showed that P. quercivorus was attracted to the volatiles emitted from fresh leaves and was not attracted to those emitted from dry leaves. This suggests that leaf volatiles from healthy hosts are primary attractants for P. quercivorus. Further, males exhibited increased olfactory responses to leaf volatiles as their flight duration increased, whereas the opposite pattern was observed in females. These results suggest that the different ecological roles of the sexes contribute to differences in olfactory responses.     

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

We 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.     

Raffaelea quercivora sp. nov. associated with mass mortality of Japanese oak, and the ambrosia beetle (Platypus quercivorus)

 A hyphomycete consistently isolated from dead oak trees (Quercus serrata and Q. mongolica var. grosseserrata) attacked by the ambrosia beetle Platypus quercivorus in Japan is described and illustrated as Raffaelea quercivora sp. nov. The new species is characterized by having small obovoid to pyriform sympodioconidia and slender, long conidiophores that taper to a point. The fungus has been isolated from the body surfaces and mycangia of the beetle. It is likely that the fungus was transferred to oak trees by P. quercivorus. Received: August 20, 2001 / Accepted: March 14, 2002     

Ambrosia beetles (Curculionidae: Scolytinae and Platypodinae) on Fagus crenata Blume: community structure,seasonal population trends and resource utilization patterns

Ambrosia beetles (many Scolytinae and all Platypodinae) are one of the most important insect pests for forestry worldwide, but little is known about the community structure of ambrosia beetles in terms of their vertical variations and resource utilization. We clarified the community structure and seasonal population trends of ambrosia beetles on 11 living and three newly dead Fagus crenata Blume trees using individual tube traps placed up to 10 m high from May to November in 2007 and 2008. We captured seven scolytine species (Ambrosiodmus lewisi (Blandford), Euwallacea validus (Eichhoff), Trypodendron proximum (Niisima), Xyleborinus saxeseni (Ratzeburg), Xyleborus atratus Eichhoff, Xylosandrus brevis (Eichhoff) and Xylosandrus germanus (Blandford)) and three platypodine species (Crossotarsus niponicus Blandford, Platypus hamatus Blandford and Platypus severini Blandford). The ambrosia beetles were suggested to breed at species‐specific height ranges, with the equal host resource use per individual among the species. Of the three major species, C. niponicus, P. hamatus and P. severini, two (C. niponicus and P. hamatus) had male‐biased sex ratios, which is considered a reproductive strategy to increase maternal fitness. Morphological characteristics of the mandibles may play an important role in the difference of sex roles on reproduction in the three major species.     

Phototactic behavior of the ambrosia beetle <Emphasis Type="Italic">Platypus quercivorus</Emphasis> (Murayama) (Coleoptera: Platypodidae) before and after flight

The ambrosia beetle Platypus quercivorus (Coleoptera: Platypodidae) is a vector of the pathogenic fungi, Raffaelea quercivora (Ophiostomatales: Ophiostomataceae), which causes Japanese oak wilt disease. Previous studies have shown that the beetle displays positive phototactic behavior; however, the adaptive significance of this behavior remains unclear. We postulated that positive phototaxis is necessary to allow the beetle to fly skyward immediately after emergence from a tree, and that this taxis changes following a certain period of flight. The present study aimed to clarify the changes in phototactic behavior of P. quercivorus before and after flight by using individual beetles emerging from the trunk of a Quercus crispula (Fagales: Fagaceae) tree that was attacked in 2014. The response of 60 beetles to light was tested ten times each, before and after flight in a flight mill. A generalized linear mixed model was constructed to predict the probability of positive phototaxis of P. quercivorus before and after flight. A best-fit model showed that the probability of positive phototaxis was lower after flight than before. The results suggest that positive phototaxis of P. quercivorus is decreased after flight.     

The effect of stem density on the probability of attack by the ambrosia beetle Platypus quercivorus varies with spatial scale

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Identification of the ambrosia fungus of <Emphasis Type="Italic">Xyleborus monographus</Emphasis> and <Emphasis Type="Italic">X. dryographus</Emphasis> (Coleoptera: Curculionidae,Scolytinae)

The scolytid ambrosia beetles Xyleborus monographus and X. dryographus were investigated to identify their nutritional ambrosia fungi. The examination of the oral mycetangia of the beetles, the specialized organs for fungal transport, revealed the dominant occurrence of Raffaelea montetyi, a fungus that was also predominant in the beetle tunnels in the immediate vicinity of the feeding larvae. R. montetyi was previously known only as the ambrosia fungus of the platypodid ambrosia beetle, Platypus cylindrus. These beetle species inhabit the same habitat, mainly trunks of oaks in the Western Palaeartic. The possibility of an exchange of the symbiotic fungus between the ambrosia beetles within their common breeding place is discussed. Consequently, the previous hypothesis of a species-specific association of a single ambrosia fungus with a single beetle species is questioned. A phylogenetic analysis based on DNA sequences classified R. montetyi within the Ophiostomatales of the ascomycetes. The investigation of conidiogenesis of R. montetyi by SEM supported this taxonomic placement and showed the development of the conidia by annellidic percurrent proliferation, identical to the conidiogenesis reported for many anamorph states of the Ophiostomatales.     

Development and characterization of 12 compound microsatellite markers in <Emphasis Type="Italic">Platypus </Emphasis><Emphasis Type="Italic">quercivorus</Emphasis> (Murayama) (Coleoptera: Platypodidae)

Twelve compound microsatellite loci were isolated from the ambrosia beetle Platypus quercivorus. Every locus was polymorphic among 50 individuals from two localities, with two to six alleles per locus, without linkage disequilibrium. The observed and expected heterozygosities ranged from 0.140 to 0.740 and from 0.255 to 0.731, respectively. These markers will be available for population genetic studies and parentage analysis of this beetle.     

Ethanol‐injection induces attacks by ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) on a variety of tree species

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Attraction of ambrosia and bark beetles to coast live oaks infected by Phytophthora ramorum

1 Sudden oak death is caused by the apparently introduced oomycete, Phytophthora ramorum. We investigated the role of bark and ambrosia beetles in disease progression in coast live oaks Quercus agrifolia. 2 In two Marin County, California sites, 80 trees were inoculated in July 2002 with P. ramorum and 40 were wounded without inoculation. Half of the trees in each group were sprayed with the insecticide permethrin [cyclopropanecarboxylic acid, 3‐(2,2‐dichloroethenyl)‐2,2‐dimethyl‐(3‐phenoxyphenyl) methyl ester] to prevent ambrosia and bark beetle attacks, and then were sprayed twice per year thereafter. After each treatment, sticky traps were placed on only the permethrin‐treated trees. Beetles were collected periodically in 2003. 3 Inoculated trees accounted for 95% of all beetles trapped. The ambrosia beetles Monarthrum scutellare and Xyleborinus saxeseni and the western oak bark beetle Pseudopityophthorus pubipennis were the most abundant of the seven species trapped. 4 Permethrin treatment delayed initiation of beetle attacks and significantly reduced the mean number of attacks per tree. Beetles did not attack any wounded or noncankered inoculated trees. 5 Trees with larger cankers trapped more beetles early in the disease. Once permethrin lost effectiveness, the number of beetle entrance tunnels was a more reliable predictor of subsequent trap catch than was canker size. 6 Beetles were initially attracted to P. ramorum cankers in response to kairomones generated in the host‐pathogen interaction. After beetles attacked the permethrin‐treated trees, aggregation pheromones most probably were the principal factor in beetle colonization behaviour.     

Freeze stress of deciduous trees induces attacks by opportunistic ambrosia beetles

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Suitability of California bay laurel and other species as hosts for the non‐native redbay ambrosia beetle and granulate ambrosia beetle

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Ability of stress‐related volatiles to attract and induce attacks by Xylosandrus germanus and other ambrosia beetles

• 1 Xylosandrus germanus typically colonizes physiologically‐stressed deciduous hosts but it is increasingly being recognized as a key pest of ornamental nursery stock. We tested the attractiveness of common plant stress‐related volatiles to ambrosia beetles occupying the nursery agroecosystem, as well as their ability to induce attacks on selected trees. Experiments were conducted in Ohio, U.S.A.
• 2 Stress volatile attractiveness was first assessed by positioning traps baited with acetaldehyde, acetone, ethanol and methanol in ornamental nurseries. Cumulative trap counts confirmed that ethanol was the most attractive stress‐related volatile to X. germanus. Methanol‐baited traps were slightly attractive to X. germanus, whereas traps baited with acetaldehyde and acetone were not attractive to any ambrosia beetle.
• 3 A series of tree injection experiments were also conducted to determine the ability of these volatiles to induce attacks by ambrosia beetles under field conditions. Injection of ethanol into Magnolia virginiana induced the largest number of attacks, whereas injection of acetaldehyde induced more attacks than methanol or acetone. Xylosandrus germanus was the most predominant species emerging from M. virginiana injected with each of the stress‐related volatiles. No attacks by wood‐boring beetles were observed on water injected or uninjected control trees.
• 4 Solid‐phase microextraction–gas chromatography–mass spectrometry confirmed the emission of acetaldehyde, acetone, ethanol and methanol after their injection into M. virginiana.
• 5 Xylosandrus germanus has an efficient olfactory‐based mechanism for differentiating among host volatile cues. Injecting select trees with stress‐related volatiles, particularly ethanol, shows promise as a trap tree strategy for X. germanus and other ambrosia beetles.

     

Ambrosia beetle response to ethanol concentration and host tree species

Ethanol emitted by stressed trees is an olfactory cue used by ambrosia beetles (Coleoptera; Curculionidae; Scolytinae) to locate susceptible hosts to colonize. In addition, ethanol enhances the growth of ambrosia beetle fungal symbionts, improving colonization. Whether host selection and colonization are affected also by the amount of ethanol produced by stressed trees and by tree species is unclear. To investigate these mechanisms, we induced attacks by ambrosia beetles in bolts of eight tree species by coring and filling them with either 5% or 90% ethanol solutions in water. For each ethanol concentration, bolts of the eight different tree species were replicated six times in a randomized complete block design. Entry holes were used as a proxy for host selection whereas gallery development stage was used as a proxy for colonization. Ethanol concentration differentially affected host selection of the three ambrosia beetles that were active during this study. Anisandrus dispar Fabricius preferentially attacked bolts with 90% ethanol concentration, Xylosandrus crassiusculus (Motschulsky) preferentially attacked bolts with 5% ethanol concentration, and Xyleborinus saxesenii (Ratzeburg) attacked bolts irrespective of ethanol concentration. Colonization of X. crassiusculus reflected the same pattern observed for entry holes. The effect of host tree species on host selection was most prominent for X. saxesenii, while X. crassiusculus established a higher number of developed galleries in Ostrya carpinifolia Scopoli bolts than on five of the other tested tree species. Our results suggest that ethanol concentration and host tree species may influence ecological niche partitioning among ambrosia beetle species.     

Real‐time PCR identification of the ambrosia beetles,Trypodendron domesticum (L.) and Trypodendron lineatum (Olivier) (Coleoptera: Scolytidae)

The European hardwood ambrosia beetle (Trypodendron domesticum) and the striped ambrosia beetle (Trypodendron lineatum) are wood‐boring pests that can cause serious damage to lumber, resulting in a need for management of these pests in logging and lumber industries. Natural populations of ambrosia beetles exist throughout the world, but movement of ambrosia beetles into new habitats, particularly via international trade, can result in the establishment of invasive species that have the potential to spread into new territory. Efforts to monitor ambrosia beetle populations are time‐consuming and could be greatly enhanced by the use of molecular methods, which would provide accurate and rapid identification of potentially problematic species. Here, we present new real‐time PCR assays for the detection and identification of T. domesticum and T. lineatum. The methods described herein can be used with a variety of sampling strategies to enable timely and well‐informed decision‐making in efforts to control these ambrosia beetles.     

Development of microsatellite markers for Pasania edulis (Makino) Makino, one of the dominant species of lucidphyllous forests in southern Kyushu, Japan

Pasania edulis (Makino) Makino is a Fagaceous tree species endemic to Japan and one of the dominant species in lucidphyllous forests in southern Kyushu, Japan. Recently, P. edulis was attacked by ambrosia beetles, Platypus quereivorus (Murayama) and mass mortality occurred in several areas in southern Kyushu. We isolated and characterized ten microsatellite loci in this species to reveal the genetic structure and gene flow. The number of alleles ranged from 3 to 11 and expected heterozygosities from 0.3761 to 0.8346. The markers described here will be useful for investigating the genetic diversity, genetic structure and gene flow, and planning for conservation of viable population of P. edulis.     

Continuous population estimates forDendroctonus frontalis Zimm. (Coleoptera: Scolytidae) occurring in infestations

Infestations of Dendroctonus frontalisZimm. are often observed to enlarge continuously by the colonization of new hosts in a pattern similar to a forest fire. This pattern of infestation growth presents unique problems in quantitatively estimating populations of D. frontalis. Beetle populations on each infested tree in an infestation go through five processes: attack, oviposition, reemergence, survivorship, and emergence. These processes, which have been described mathematically in the literature, each take several days for completion. In order to follow the distribution and abundance of D. frontalis throughout the course of development of a spot, we need a daily estimate of the number of beetles involved in each process on every tree. Since it is not practical to sample each tree daily, we developed a procedure whereby quantitative estimation procedures for within-tree populations were used in combination with the mathematical models for the life processes to produce a daily record of the number of adults successfully attacking trees, the number of eggs oviposited, the number of beetles reemerging, number of beetles surviving within the trees, and the number of beetles emerging. These daily estimates were then summarized for all trees in the spot for the duration of the infestation. The daily record of populations of D. frontalis, used with information on infestation geometry, were suggested to be of value in describing and elucidating several important facets of population dynamics including dispersal patterns within infestations, between tree beetle loss (mortality), and time lags among the various population processes. The information reported can be used to develop simulation models of population dynamics or to validate existing models.     

Fungus Symbionts Colonizing the Galleries of the Ambrosia Beetle <Emphasis Type="Italic">Platypus quercivorus</Emphasis>

Isolations were made to determine the fungal symbionts colonizing Platypus quercivorus beetle galleries of dead or dying Quercus laurifolia, Castanopsis cuspidata, Quercus serrata, Quercus crispula, and Quercus robur. For these studies, logs from oak wilt-killed trees were collected from Kyoto Prefecture, Japan. Fungi were isolated from the: (1) entrances of beetle galleries, (2) vertical galleries, (3) lateral galleries, and (4) the larval cradle of P. quercivorus in each host tree. Among the fungus colonies which appeared on YM agar plates, 1,219 were isolated as the representative isolates for fungus species inhabiting in the galleries based on their cultural characteristics. The validity of the visual classification of the fungus colonies was checked and if necessary properly corrected using microsatellite-primed PCR fingerprints. The nucleotide sequence of the D1/D2 region of the large subunit nuclear rRNA gene detected 38 fungus species (104 strains) of which three species, i.e., Candida sp. 3, Candida kashinagacola (both yeasts), and the filamentous fungus Raffaelea quercivora were isolated from all the tree species. The two yeasts were most prevalent in the interior of galleries, regardless of host tree species, suggesting their close association with the beetle. A culture-independent method, terminal restriction fragment length polymorphism (T-RFLP) analysis was also used to characterize the fungus flora of beetle galleries. T-RFLP patterns showed that yeast species belonging to the genus Ambrosiozyma frequently occurred on the gallery walls along with the two Candida species. Ours is the first report showing the specific fungi inhabiting the galleries of a platypodid ambrosia beetle.     

Ambrosia beetle (Coleoptera: Scolytidae) species, flight, and attack on living eastern cottonwood trees

In spring 2002, ambrosia beetles (Coleoptera: Scolytidae) infested an intensively managed 22-ha tree plantation on the upper coastal plain of South Carolina. Nearly 3,500 scolytids representing 28 species were captured in ethanol-baited traps from 18 June 2002 to 18 April 2004. More than 88% of total captures were exotic species. Five species [Dryoxylon onoharaensum (Murayama), Euwallacea validus (Eichhoff), Pseudopityophthorus minutissimus (Zimmermann), Xyleborus atratus Eichhoff, and Xyleborus impressus Eichhoff]) were collected in South Carolina for the first time. Of four tree species in the plantation, eastern cottonwood, Populus deltoides Bartram, was the only one attacked, with nearly 40% of the trees sustaining ambrosia beetle damage. Clone ST66 sustained more damage than clone S7C15. ST66 trees receiving fertilization were attacked more frequently than trees receiving irrigation, irrigation + fertilization, or controls, although the number of S7C15 trees attacked did not differ among treatments. The study location is near major shipping ports; our results demonstrate the necessity for intensive monitoring programs to determine the arrival, spread, ecology, and impact of exotic scolytids.