Verbenone reduces landing of the redbay ambrosia beetle,vector of the laurel wilt pathogen,on live standing redbay trees

1. Laurel wilt is a disease that has caused extensive mortality of redbay Persea borbonia in the southeastern U.S.A. The redbay ambrosia beetle Xyleborus glabratus is the vector of the causal agent of laurel wilt, the fungus Raffaelea lauricola.
2. We tested two potential repellents to the redbay ambrosia beetle, verbenone and methyl salicylate (MeSA) in an 8‐month large‐scale experiment conducted in three locations in Florida. In each location, redbay trees were treated with a single or double application of SPLAT (Specialized Pheromone and Lure Application Technology; ISCA Technologies, Riverside, California) verbenone, as well as SPLAT with a 1:2 mix of MeSA and verbenone.
3. The MeSA + verbenone mixes did not reduce beetle captures compared with the control treatment, whereas SPLAT verbenone alone significantly reduced the number of beetles captured on sticky traps placed on redbay trees in the three locations. The reduction of beetle capture was similar regardless of one or two treatments of SPLAT verbenone. The reduction of tree death with the SPLAT verbenone treatment was not statistically significant.
4. The results of the present study suggest that trunk application of verbenone can reduce landing rates of the redbay ambrosia beetle on live redbay trees and shows promise for use in an integrated pest management strategy against laurel wilt.

     

Entomopathogenic fungi as biological control agents for the vector of the laurel wilt disease,the redbay ambrosia beetle,Xyleborus glabratus (Coleoptera: Curculionidae)

The redbay ambrosia beetle (RAB), Xyleborus glabratus, is a wood-boring insect that vectors the fungal pathogen, Raffaelea lauricola, which causes laurel wilt, a lethal disease of avocado. The objective of this study was to determine the susceptibility of RAB to infection and subsequent death by exposure to three commercial strains of entomopathogenic fungi [two strains of Isaria fumosorosea (Ifr 3581 and PFR), and strain GHA of Beauveria bassiana]. RAB females were dipped in fungal spore solutions and their median survivorship times (MST) determined. Contact with any of the biopesticides resulted in death of all RAB females. MSTs of RAB females ranged from 3 days (B. bassiana) to 5 days (I. fumosorosea PFR). B. bassiana killed RAB females faster, followed by Ifr 3581 and PFR. RAB females dipped in B. bassiana suspensions had the highest number of viable spores attached to their bodies, followed by Ifr 3581. Beetles dipped in PFR suspension had significantly less viable spores attached to their bodies. No significant differences were observed in the mortality of beetles exposed to entomopathogenic fungi by dipping in a fungal suspension or walking on treated avocado bolts. Beetles bored into the logs and constructed galleries, but they were found dead inside the galleries a few days after exposure to the entomopathogens. Entomopathogenic fungal infection in dead beetles was confirmed through molecular techniques. This is the first study to demonstrate that entomopathogenic fungi are potential biological control agents against RAB.     

Risk assessment of Hass avocado and Mexican Lauraceae for attack by redbay ambrosia beetle (Coleoptera: Curculionidae: Scolytinae)

1. The redbay ambrosia beetle, Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae), vectors the mycopathogen that causes laurel wilt, a lethal vascular disease of trees in the Lauraceae. Since being detected in Georgia, USA in 2002, this invasive pest has become established in 11 additional states.
2. With continued spread, X. glabratus will likely enter Mexico. In advance of this event, this study was initiated to assess the risk posed to eight native laurels and Hass avocados, the predominant cultivar grown in Mexico.
3. Wood bolts from each species were used in (a) field tests to determine the relative attraction of female X. glabratus, (b) laboratory bioassays to evaluate boring preferences, and (c) GC–MS analyses to identify host kairomones. For comparison, tests included control bolt treatments consisting of silkbay (an attractive U.S. laurel) and Simmonds avocado (a Florida cultivar susceptible to laurel wilt).
4. Hass avocado and two native laurels (Persea schiedeana and Ocotea heribertoi vel aff.) were highly attractive to females and elicited strong boring responses. These species were high in sesquiterpene hydrocarbons, including α-copaene and α-cubebene.
5. Results of this study suggest that X. glabratus could become a serious agricultural and forest pest upon incursion into Mexico, with severe economic and ecological impacts.

     

Evaluation of repellents for the redbay ambrosia beetle,Xyleborus glabratus,vector of the laurel wilt pathogen

The redbay ambrosia beetle, Xyleborus glabratus, is the vector of the laurel wilt disease fungal pathogen, Raffaelea lauricola. Since the vector's initial detection in the USA in the early 2000s, laurel wilt has killed millions of redbay, Persea borbonia, trees and other members of the plant family Lauraceae. To protect host trees from beetle attack and laurel wilt infection, we tested the efficacy of host‐ and non‐host‐derived and commercial compounds as X. glabratus repellents in field experiments. In our first trial, the major constituents of the non‐host tree, longleaf pine, Pinus palustris, and SPLAT Verb (verbenone 10%) were paired with manuka oil attractants and beetle captures were counted. Verbenone and a 1 : 1 blend of myrcene and camphene were intermediate to both the manuka positive and blank negative controls. Subsequently, we tested different blends of methyl salicylate (MeSA), a host defence and signalling compound, and verbenone in SPLAT dispensers using freshly cut redbay bolts as an attractant. All treatments reduced X. glabratus captures and boring holes as compared to the redbay (‐) repellent positive control; however, SPLAT Verb and SPLAT MeSA‐Verb (5% each) achieved the highest repellency, with results comparable to that of the non‐host (laurel oak). These trials establish that host‐derived and commercially available repellent compounds can reduce X. glabratus attacks and therefore have potential as part of an integrated management strategy against laurel wilt and its vector.     

Effect of trap type, trap position, time of year, and beetle density on captures of the redbay ambrosia beetle (Coleoptera: Curculionidae: Scolytinae)

The exotic redbay ambrosia beetle, Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae), and its fungal symbiont Raffaellea lauricola Harrington, Fraedrich, and Aghayeva are responsible for widespread redbay, Persea borbonia (L.) Spreng., mortality in the southern United States. Effective traps and lures are needed to monitor spread of the beetle and for early detection at ports-of-entry, so we conducted a series of experiments to find the best trap design, color, lure, and trap position for detection of X. glabratus. The best trap and lure combination was then tested at seven sites varying in beetle abundance and at one site throughout the year to see how season and beetle population affected performance. Manuka oil proved to be the most effective lure tested, particularly when considering cost and availability. Traps baited with manuka oil lures releasing 5 mg/d caught as many beetles as those baited with lures releasing 200 mg/d. Distributing manuka oil lures from the top to the bottom of eight-unit funnel traps resulted in similar numbers of X. glabratus as a single lure in the middle. Trap color had little effect on captures in sticky traps or cross-vane traps. Funnel traps caught twice as many beetles as cross-vane traps and three times as many as sticky traps but mean catch per trap was not significantly different. When comparing height, traps 1.5 m above the ground captured 85% of the beetles collected but a few were caught at each height up to 15 m. Funnel trap captures exhibited a strong linear relationship (r2 = 0.79) with X. glabratus attack density and they performed well throughout the year. Catching beetles at low densities is important to port of entry monitoring programs where early detection of infestations is essential. Our trials show that multiple funnel traps baited with a single manuka oil lure were effective for capturing X. glabratus even when no infested trees were visible in the area.     

Effect of tree species and end seal on attractiveness and utility of cut bolts to the redbay ambrosia beetle and granulate ambrosia beetle (coleoptera: Curculionidae: Scolytinae)

The redbay ambrosia beetle, Xyleborus glabratus Eichhoff, is a non-native invasive pest and vector of the fungus that causes laurel wilt disease in certain trees of the family Lauraceae. This study assessed the relative attractiveness and suitability of cut bolts of several tree species to X. glabratus. In 2009, female X. glabratus were equally attracted to traps baited with swampbay (Persea palustris (Rafinesque) Sargent) and camphortree (Cinnamomum camphora (L.) J. Presl), which were more attractive than avocado (Persea americana Miller), lancewood (Ocotea coriacea (Swartz) Britton), and sweetbay (Magnolia virginiana L.). These species were more attractive than loblolly bay (Gordonia lasianthus (L.) J. Ellis). X. glabratus entrance hole density and emergence from caged bolts were highest on swampbay and camphortree. In 2010, swampbay was significantly more attractive to X. glabratus than sassafras (Sassafras albidum (Nuttall) Nees), yellow poplar (Liriodendron tulipifera L.), and eastern redbud (Cercis canadensis L.). Sassafras bolts end sealed with a liquid wax-and-water emulsion were more attractive to X. glabratus than end-sealed bolts of yellow poplar and redbud. Relative to unsealed bolts, end seal decreased X. glabratus entrance hole density on swampbay and decreased granulate ambrosia beetle (Xylosandrus crassiusculus (Motschulsky)) trap catch, entrance hole density, and adult emergence from swampbay. X. crassiusculus was not attracted to sassafras, yellow poplar, and redbud and was not more attracted to manuka oil than to unbaited traps. Sassafras was more attractive to X. glabratus than previously reported and supported reproducing populations of the insect. End sealing bolts with a wax-and-water emulsion may not be optimal for attracting and rearing ambrosia beetles in small logs.     

The influence of forest stand and site characteristics on the composition of exotic dominated ambrosia beetle communities (Coleoptera: Curculionidae: Scolytinae)

Economic and biological consequences are associated with exotic ambrosia beetles and their fungal associates. Despite this, knowledge of ambrosia beetles and their ecological interactions remain poorly understood, especially in the oak-hickory forest region. We examined how forest stand and site characteristics influenced ambrosia beetle habitat use as evaluated by species richness and abundance of ambrosia beetles, both the native component and individual exotic species. We documented the species composition of the ambrosia beetle community, flight activity, and habitat use over a 2-yr period by placing flight traps in regenerating clearcuts and older oak-hickory forest stands differing in topographic aspect. The ambrosia beetle community consisted of 20 species with exotic ambrosia beetle species dominating the community. Similar percentages of exotic ambrosia beetles occurred among the four forest habitats despite differences in stand age and aspect. Stand characteristics, such as stand age and forest structure, influenced ambrosia beetle richness and the abundances of a few exotic ambrosia beetle species and the native ambrosia beetle component. Topographic aspect had little influence on ambrosia beetle abundance or species richness. Older forests typically have more host material than younger forests and our results may be related to the amount of dead wood present. Different forms of forest management may not alter the percent contribution of exotic ambrosia beetles to the ambrosia beetle community.     

Semiochemical emission from individual galleries of the southern pine beetle, (Coleoptera: Curculionidae: Scolytinae), attacking standing trees

We collected, identified, and quantified volatiles arising from individual gallery entrances of the monogamous bark beetle Dendroctonus frontalis Zimmermann. Samples were collected while the insects were mass attacking mature loblolly pines (Pinus taeda L.) in an established infestation in western Mississippi, 1 August through 3 October 2005. Following volatile sample collection, the entrances were dissected and categorized according to those that 1) contained a solitary female (the gallery initiating sex), 2) contained a pair that had not yet produced an egg gallery, 3) led to an egg gallery with niches and/or eggs, or 4) represented failed attacks (either abandoned or containing dead beetles). The greatest mean release rate of the female-produced aggregation pheromone components frontalin (74 ng/h) and trans-verbenol (0.35 microg/h) was detected from entrances of solitary females, whereas the highest mean quantities of the male-produced multifunctional pheromone components endo-brevicomin (18 ng/h) and verbenone (0.15 microg/h) were detected from entrances of preoviposition beetle pairs. Alpha-pinene, a host-produced monoterpene that functions as a synergist for the aggregation attractant for D. frontalis, was detected from entrances of solitary females and preoviposition pairs at a rate of 0.6 mg/h, or 3-4 orders of magnitude greater than the insect-produced components of the attractant. Our results indicate that the release rates of pheromone components used in published field studies of the chemical ecology of D. frontalis (generally > 0.1 mg/h) represent thousands of 'attack equivalents' or production rates on the scale of a beetle mass attack on a single host. Additionally, our data suggest that the loss in attractiveness of host tissue fully colonized by D. frontalis is because of the disappearance of attractants rather than an increase in inhibitors.     

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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Phenological observations and trapping tactics for the granulate ambrosia beetle Xylosandrus crassiusculus (Coleoptera: Curculionidae,Scolytinae) in New Zealand

1. The granulate ambrosia beetle (GAB) Xylosandrus crassiusculus, was first formally detected in New Zealand in 2019. Since then, GAB has subsequently been found infesting numerous tree species in the Auckland region.
2. Flight intercept traps baited with ethanol lures were deployed from October 2019 to May 2021 at three sites in the Auckland region to ascertain the phenology of GAB in New Zealand. Two distinct peak flight periods were identified in early and late summer, while a smaller and inconsistent third peak was detected in early autumn. Logistical analysis of GAB captures in the ethanol-lured traps and degree-day (DD) accumulation indicated that 90% of flight activity is completed by 800 DD.
3. To assess monitoring tactics, flight intercept traps were baited with three different ethanol lures with varying release rates or ethanol-soaked or non-soaked wood bolts from three species of trees. A lure releasing 2 g ethanol per day was most effective at capturing GAB. Ethanol-soaked bolts were less effective than the lures.
4. Xylosandrus crassiusculus represents a significant risk for shrubs and trees native to New Zealand, as well as commercial horticultural and forestry trees. We recommend using ethanol-lured panel traps for monitoring purposes.

     

Isolations from the redbay ambrosia beetle, Xyleborus glabratus, confirm that the laurel wilt pathogen, Raffaelea lauricola, originated in Asia

The laurel wilt pathogen Raffaelea lauricola was hypothesized to have been introduced to the southeastern USA in the mycangium of the redbay ambrosia beetle, Xyleborus glabratus, which is native to Asia. To test this hypothesis adult X. glabratus were trapped in Taiwan and on Kyushu Island, Japan, in 2009, and dead beetles were sent to USA for isolation of fungal symbionts. Individual X. glabratus were macerated in glass tissue grinders, and the slurry was serially diluted and plated onto malt agar medium amended with cycloheximide, a medium semiselective for Ophiostoma species and their anamorphs, including members of Raffaelea. R. lauricola was isolated from 56 of 85 beetles in Taiwan and 10 of 16 beetles in Japan at up to an estimated 10 000 CFUs per beetle. The next most commonly isolated species was R. ellipticospora, which also has been recovered from X. glabratus trapped in the USA, as were two other fungi isolated from beetles in Taiwan, R. fusca and R. subfusca. Three unidentified Raffaelea spp. and three unidentified Ophiostoma spp. were isolated rarely from X. glabratus collected in Taiwan. Isolations from beetles similarly trapped in Georgia, USA, yielded R. lauricola and R. ellipticospora in numbers similar to those from beetles trapped in Taiwan and Japan. The results support the hypothesis that R. lauricola was introduced into the USA in mycangia of X. glabratus shipped to USA in solid wood packing material from Asia. However differences in the mycangial mycoflora of X. glabratus in Taiwan, Japan and USA suggest that the X. glabratus population established in USA originated in another part of Asia.     

Biology of two members of the Euwallacea fornicatus species complex (Coleoptera: Curculionidae: Scolytinae), recently invasive in the U.S.A., reared on an ambrosia beetle artificial diet

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The infestation and habitat of the ambrosia beetle Euwallacea interjectus (Coleoptera: Curculionidae: Scolytinae) in the riparian zone of Shanghai,China

1. Extensive boring damage into trunks of living poplar trees in the urban forest of Shanghai, eastern China, was investigated in 2017.
2. In order to determine the taxonomic identity of the pest, we used morphological identification and sequenced mitochondrial COI gene. Based on both morphology and molecular data, it was concluded that the pest boring into the poplars was the ambrosia beetle Euwallacea interjectus (Blandford).
3. Its occurrence and damage on poplar across Shanghai were also investigated. In the Pudong District, a total of 104.52 ha of urban forest were investigated thoroughly, and 16.22% of surveyed forests were found to be infested. This insect species is an important native pest capable of causing damage across the Shanghai area.
4. Observations in the field suggested that the damage may be related to distance to water sources. Our statistical analysis confirmed this hypothesis, as the close distance to water bodies correlated with higher levels of damage. We conclude that E. interjectus prefers host trees stressed by an occasional excessive abundance of water, and acts as a parasite on living trees without killing them.

     

An attack of Ips amitinus (Coleoptera: Curculionidae: Scolytinae) on arboretum in West Siberia: New host of invasive bark beetle among exotic conifers

Invasive populations of small spruce bark beetle Ips amitinus were first registered in 2019 in the southeast of Western Siberia. In natural stands of Siberian pine (Pinus sibirica Du Tour), several hundred hectares of outbreak foci of the alien bark beetle were identified. In 2020, a local focus of the bark beetle was found in the conifer collection in the arboretum “Kedr” of the Institute of Monitoring Climatic and Ecological Systems SB RAS, 30 km from Tomsk. The bark beetle caused the main damage to the collection of pines. I. amitinus colonized both host plants Scotch pine (Pinus sylvestris L.) and mountain pine (Pinus mugo Turra), which were previously known to it in the native range in Europe, and the local Siberian species Siberian pine (Pinus sibirica Du Tour), Siberian spruce (Picea obovata Ledeb.) and introduced Far Eastern Korean pine (Pinus koraiensis Sieb. et Zucc.). Demographic characteristics of I. amitinus studied on damaged trees indicate its high reproduction potential in Siberia. The bark beetle outbreak focus was suppressed; however, this plantation requires further annual monitoring of pest abundance and distribution, both to preserve the scientific dendroecological field station and to study the implementation of sential plant conception in relation to the invasion of I. amitinus.     

Fitness consequences of pheromone production and host selection strategies in a tree-killing bark beetle (Coleoptera: Curculionidae: Scolytinae)

Timing of arrival at a resource often determines an individual’s reproductive success. Tree-killing bark beetles can reproduce in healthy trees by attacking in adequate numbers to overcome host defences that could otherwise be lethal. This process is mediated by aggregation and antiaggregation pheromones. Beetles that arrive early in such a “mass attack” must contend with undiminished tree defences, and produce enough pheromones to attract more beetles, but have a head start on gallery construction and egg-laying. Beetles that arrive late may be impeded by competition and diminishing availability of phloem, but should experience fewer costs associated with pheromone production and battling tree defences. We investigated relationships between timing of arrival, body size, pheromone production and fitness in the southern pine beetle, Dendroctonus frontalis. In field experiments, we captured beetles that arrived early (pioneers) and late on slash pine trees, Pinus elliottii, and measured pheromone amounts in their hindguts. We marked gallery entrances of beetles as they landed on a tree and measured their reproductive success after the attack terminated. We found no difference in body size or pheromone amounts between early and late arrivers. Most beetles arrived at the middle of the attack sequence, and excavated longer galleries per day than early arrivers. The number of offspring produced per day by beetles that established galleries midway through mass attack was higher than those that arrived early or very late in the sequence. Our results suggest that beetles do not exhibit adaptive phenotypic plasticity in pre-landing pheromone production, depending on the extent of previous colonisation of a host. Rather, it appears that stabilising selection favours beetles that attack in the middle of the sequence, and contributes to attack synchrony. Synchronous attack on trees is essential before population booms characteristic of tree-killing bark beetles can occur in nature.     

External microstructure of the ambrosia beetle Platypus koryoensis (Coleoptera: Curculionidae: Platypodinae)

Platypus koryoensis is a minute ambrosia beetle found in forests. It can cause significant economic damage to oak trees. Recently in Korea, it has been reported as a major pest of oak trees, because it causes sooty mold of oak by introducing the pathogenic fungus Raffaelea sp. In this paper, we demonstrate the fine structural aspects of the external body of the ambrosia beetle using field emission scanning electron microscopy, as a part of basic research into this pest so that strategies for its control might be developed. This beetle has a sensory system well developed to respond to both visual and chemical stimuli. Both sexes have a pair of faceted compound eyes and a pair of knobbed antennae, but simple eyes are absent. The mouthparts on its distinct snouts are effective devices for penetration and for boring holes. The mouthparts consist of the labrum, a pair of mandibles, a pair of maxillae and the labium. Both the maxillary and the labial palpi have the function of directing the food to the mouth and holding it while the mandibles chew the food. The distal ends of these palpi are flattened and have shovel‐like setae. The thorax has a particularly hard exoskeleton and hard elytra, including powerful muscles that operate both the wings and the legs. The legs are multi‐segmented and have a strong femur and tibia, including one pair of claws on the end of each tarsal segment. Characteristically, both male and female beetles have mycangial cavities for storing spores and other microorganisms, but only females have three pairs of large depressions on their dorsal thorax.     

危害猕猴桃的新害虫——端齿材小蠹

【目的】本文描述了首次在贵州猕猴桃上发生的一种害虫——端齿材小蠹Anisandrus apicalis(Blandford)。【方法】通过对当地修文县谷堡乡平滩村猕猴桃病树上小蠹的观察和形态研究,进行分类和鉴定。【结果】此次发现的端齿材小蠹是贵州省境内第一次报道,也是首次发现在猕猴桃病枝上发生。本文提供了该小蠹的分类和鉴别,附有相关近缘种的形态特征图和检索表,并介绍了其寄主和分布,以及在贵阳修文猕猴桃的危害和发生等情况。【结论】此次发生在猕猴桃上的端齿材小蠹是贵州省境内的首例,本文结果可以为当地植物检疫和猕猴桃种植管理提供参考。虽然此次端齿材小蠹在猕猴桃上发生,但是未发现其会直接为害猕猴桃健康植株,需要在将来进行深入的实验调查。     

Phylogeography of the bark beetle Dendroctonus mexicanus Hopkins (Coleoptera: Curculionidae: Scolytinae)

Dendroctonus mexicanus is polyphagous within the Pinus genus and has a wide geographical distribution in Mexico and Guatemala. We examined the pattern of genetic variation across the range of this species to explore its demographic history and its phylogeographic pattern. Analysis of the mtDNA sequences of 173 individuals from 25 Mexican populations allowed to us identify 53 geographically structured haplotypes. High haplotype and low nucleotide diversities and Tajima’s D indicate that D. mexicanus experienced rapid population expansion during its dispersal across mountain systems within its current range. The nested clade phylogeographic analysis indicates that the phylogeographic pattern of D. mexicanus is explained by continuous dispersion among lineages from the Sierra Madre Occidental, the Sierra Madre Oriental and the Trans-Mexican Volcanic Belt. However, we also observed isolation events among haplotypes from the Cofre de Perote/Trans-Mexican Volcanic Belt/Sierra Madre Oriental and the Trans-Mexican Volcanic Belt/Sierra Madre del Sur, which is consistent with the present conformation of mountain systems in Mexico and the emergence of geographical barriers during the Pleistocene.     

Genetic structure of Japanese populations of an ambrosia beetle,Xylosandrus germanus (Curculionidae: Scolytinae)

We examined the genetic structures of 13 Japanese populations of an ambrosia beetle, Xylosandrus germanus (Curculionidae: Scolytinae), to understand the effects of geographical barriers on the colonization dynamics of this species. The genetic structure was studied using portions of the mitochondrial cytochrome oxidase I (COI) gene. A phylogenetic analysis revealed three distinct lineages (clades A, B and C) within X. germanus. Clade A contained 21 haplotypes from all 13 populations; whereas clade B contained eight haplotypes from Hokkaido (Sapporo and Furano), Iwate and Nagano populations; and clade C contained only a single a haplotype from the Hokkaido (Furano) population. In the analysis of molecular variance (amova ), the greatest amount of genetic variation was detected between populations in Hokkaido and those in Honshu and other southern islands. Between these two groups of populations, all the values of the coefficient of gene differentiation were significantly larger than zero, except for the Hokkaido (Sapporo) versus Nagano comparison. Our results confirm that for X. germanus, gene flow has been interrupted between Hokkaido and Honshu since the last glacial maximum.     

Mycangia of the ambrosia beetle, Austroplatypus incompertus (Schedl) (Coleoptera: Curculionidae: Platypodinae)

Abstract  Ambrosia beetles have an obligate relationship with the ambrosia fungi that they feed on. This requires that the beetles have means to transport those fungi when they colonise new hosts. Some ambrosia beetles have special structures called mycangia to transport fungi in. This paper describes the mycangia of the ambrosia beetle Austroplatypus incompertus and illustrates how the mycangical hairs are probably used by the beetle to acquire fungal spores for transport. The mycangia and probable method of fungal acquisition of this species are compared with those of other ambrosia beetles.