Xylosandrus Crassiusculus Research Articles

Comparison of Baited Bottle and Multiple-Funnel Traps for Ambrosia Beetles (Coleoptera: Curculionidae: Scolytinae) in Eastern United States1

Abstract We compared bottle traps to 4-unit multiple-funnel traps (both baited with ethanol and conophthorin) for relative efficacy in catching ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) at four locations in the eastern United States. Our results were geographically inconsistent for three target species. Catches of Xylosandrus germanus (Blandford) in Ohio were greater in bottle traps than in funnel traps while the opposite occurred in Virginia, with no difference in Indiana. Catches of Xyleborinus saxesenii (Ratzeburg) were greater in funnel traps than in bottle traps in Georgia, Indiana, and Virginia but no different in Ohio. Similarly, catches of Xylosandrus crassiusculus (Motschulsky) were greater in funnel traps than in bottle traps in Georgia and Virginia but not in Indiana. Bottle traps caught more Anisandrus maiche Stark in Ohio and Anisandrus sayi (Hopkins) in Indiana whereas more of the following species were caught in funnel traps: Ambrosiophilus atratus (Eichhoff) in Virginia, Cy...

Plasticity of mycangia in Xylosandrus ambrosia beetles

Insects that depend on microbial mutualists evolved a variety of organs to transport the microsymbionts while dispersing. The ontogeny and variability of such organs is rarely studied, and the microsymbiont's effects on the animal tissue development remain unknown in most cases. Ambrosia beetles (Coleoptera: Curculionidae: Scolytinae or Platypodinae) and their mutualistic fungi are an ideal system to study the animal-fungus interactions. While the interspecific diversity of their fungus transport organ-mycangia-is well-known, their developmental plasticity has been poorly described. To determine the ontogeny of the mycangium and the influence of the symbiotic fungus on the tissue development, we dissected by hand or scanned with micro-CT the mycangia in various developmental stages in five Xylosandrus ambrosia beetle species that possess a large, mesonotal mycangium: Xylosandrus amputatus, Xylosandrus compactus, Xylosandrus crassiusculus, Xylosandrus discolor, and Xylosandrus germanus. We processed 181 beetle samples from the United States and China. All five species displayed three stages of the mycangium development: (1) young teneral adults had an empty, deflated and cryptic mycangium without fungal mass; (2) in fully mature adults during dispersal, the pro-mesonotal membrane was inflated, and most individuals developed a mycangium mostly filled with the symbiont, though size and symmetry varied; and (3) after successful establishment of their new galleries, most females discharged the bulk of the fungal inoculum and deflated the mycangium. Experimental aposymbiotic individuals demonstrated that the pronotal membrane invaginated independently of the presence of the fungus, but the fungus was required for inflation. Mycangia are more dynamic than previously thought, and their morphological changes correspond to the phases of the symbiosis. Importantly, studies of the fungal symbionts or plant pathogen transmission in ambrosia beetles need to consider which developmental stage to sample. We provide illustrations of the different stages, including microphotography of dissections and micro-CT scans.

Spore Acquisition and Survival of Ambrosia Beetles Associated with the Laurel Wilt Pathogen in Avocados after Exposure to Entomopathogenic Fungi.

Laurel wilt is a disease threatening the avocado industry in Florida. The causative agent of the disease is a fungus vectored by ambrosia beetles that bore into the trees. Until recently, management strategies for the vectors of the laurel wilt fungus relied solely on chemical control and sanitation practices. Beneficial entomopathogenic fungi (EPF) are the most common and prevalent natural enemies of pathogen vectors. Laboratory experiments demonstrated that commercial strains of EPF can increase the mortality of the primary vector, Xyleborus glabratus, and potential alternative vectors, Xylosandrus crassiusculus, Xyleborus volvulus and Xyleborus bispinatus (Coleoptera: Curculionidae: Scolytinae). Our study provides baseline data for three formulated commercially-available entomopathogenic fungi used as potential biocontrol agents against X. crassiusculus, X. volvulus and X. bispinatus. The specific objectives were to determine: (1) the mean number of viable spores acquired per beetle species adult after being exposed to formulated fungal products containing different strains of EPF (Isaria fumosorosea, Metarhizium brunneum and Beauveria bassiana); and (2) the median and mean survival times using paper disk bioassays. Prior to being used in experiments, all fungal suspensions were adjusted to 2.4 × 106 viable spores/mL. The number of spores acquired by X. crassiusculus was significantly higher after exposure to B. bassiana, compared to the other fungal treatments. For X. volvulus, the numbers of spores acquired per beetle were significantly different amongst the different fungal treatments, and the sequence of spore acquisition rates on X. volvulus from highest to lowest was I. fumosorosea > M. brunneum > B. bassiana. After X. bispinatus beetles were exposed to the different suspensions, the rates of acquisition of spores per beetle amongst the different fungal treatments were similar. Survival estimates (data pooled across two tests) indicated an impact for each entomopathogenic fungus per beetle species after exposure to a filter paper disk treated at the same fungal suspension concentration. Kaplan–Meier analysis (censored at day 7) revealed that each beetle species survived significantly shorter in bioassays containing disks treated with EPF compared to water only. This study demonstrated that ambrosia beetles associated with the laurel wilt pathogen in avocados are susceptible to infection by EPF under laboratory conditions. However, the EPF needs to be tested under field conditions to confirm their efficacy against the beetles.

Partnerships Between Ambrosia Beetles and Fungi: Lineage-Specific Promiscuity Among Vectors of the Laurel Wilt Pathogen, Raffaelea lauricola.

Nutritional mutualisms that ambrosia beetles have with fungi are poorly understood. Although these interactions were initially thought to be specific associations with a primary symbiont, there is increasing evidence that some of these fungi are associated with, and move among, multiple beetle partners. We examined culturable fungi recovered from mycangia of ambrosia beetles associated with trees of Persea humilis (silk bay, one site) and P. americana (avocado, six commercial orchards) that were affected by laurel wilt, an invasive disease caused by a symbiont, Raffaelea lauricola, of an Asian ambrosia beetle, Xyleborus glabratus. Fungi were isolated from 20 adult females of X. glabratus from silk bay and 70 each of Xyleborus affinis, Xyleborus bispinatus, Xyleborus volvulus, Xyleborinus saxesenii, and Xylosandrus crassiusculus from avocado. With partial sequences of ribosomal (LSU and SSU) and nuclear (β-tubulin) genes, one to several operational taxonomic units (OTUs) of fungi were identified in assayed individuals. Distinct populations of fungi were recovered from each of the examined beetle species. Raffaelea lauricola was present in all beetles except X. saxesenii and X. crassiusculus, and Raffaelea spp. predominated in Xyleborus spp. Raffaelea arxii, R. subalba, and R. subfusca were present in more than a single species of Xyleborus, and R. arxii was the most abundant symbiont in both X. affinis and X. volvulus. Raffaelea aguacate was detected for the first time in an ambrosia beetle (X. bispinatus). Yeasts (Ascomycota, Saccharomycotina) were found consistently in the mycangia of the examined beetles, and distinct, putatively co-adapted populations of these fungi were associated with each beetle species. Greater understandings are needed for how mycangia in ambrosia beetles interact with fungi, including yeasts which play currently underresearched roles in these insects.

First records of Cyclorhipidion fukiense (Eggers) (Coleoptera: Curculionidae: Scolytinae: Xyleborini), an ambrosia beetle native to Asia, in North America.

The Asian ambrosia beetle, Cyclorhipidion fukiense (Eggers) was detected for the first time in North America based on three specimens trapped in 2012 from three localities in South Carolina and two other specimens intercepted at the port of Savannah, Georgia, in 2010. The species is characterized, illustrated with high-resolution images, and compared with two other congeneric, adventive species (C. bodoanum and C. pelliculosum) presently established in eastern North America. Morphometric measurements are provided and a provisional key is presented to the species of Cyclorhipidion occurring in North America.

Vertical Distribution and Daily Flight Periodicity of Ambrosia Beetles (Coleoptera: Curculionidae) in Florida Avocado Orchards Affected by Laurel Wilt.

Ambrosia beetles have emerged as significant pests of avocado ((Persea americana Mill. [Laurales: Lauraceae])) due to their association with pathogenic fungal symbionts, most notably Raffaelea lauricola T.C. Harr., Fraedrich & Aghayeva (Ophiostomatales: Ophiostomataceae), the causal agent of the laurel wilt (LW) disease. We evaluated the interaction of ambrosia beetles with host avocado trees by documenting their flight height and daily flight periodicity in Florida orchards with LW. Flight height was assessed passively in three avocado orchards by using ladder-like arrays of unbaited sticky traps arranged at three levels (low: 0-2 m; middle: 2-4 m; high: 4-6 m). In total, 1,306 individuals of 12 Scolytinae species were intercepted, but six accounted for ~95% of the captures: Xyleborus volvulus (Fabricius) (Coleoptera: Curculionidae), Xyleborinus saxesenii Ratzeburg (Coleoptera: Curculionidae), Euplatypus parallelus (Fabricius) (Coleoptera: Curculionidae), Xyleborus bispinatus Eichhoff (Coleoptera: Curculionidae), Xyleborus affinis Eichhoff (Coleoptera: Curculionidae), and Hypothenemus sp. (Coleoptera: Curculionidae). The primary vector of R. lauricola, Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae), was not detected. Females of X. volvulus showed a preference for flight at low levels and X. bispinatus for the low and middle levels; however, captures of all other species were comparable at all heights. At a fourth orchard, a baiting method was used to document flight periodicity. Females of X. saxesenii and Hypothenemus sp. were observed in flight 2-2.5 h prior to sunset; X. bispinatus, X. volvulus, and X. affinis initiated flight at ~1 h before sunset and Xylosandrus crassiusculus (Motschulsky) (Coleoptera: Curculionidae) at 30 min prior to sunset. Results suggest that ambrosia beetles in South Florida fly near sunset (when light intensity and wind speed decrease) at much greater heights than previously assumed and have species-specific patterns in host-seeking flight.

Fusarium oligoseptatum sp. nov., a mycosymbiont of the ambrosia beetle Euwallacea validus in the Eastern U.S. and typification of F. ambrosium.

Fusarium oligoseptatum sp. nov. was isolated from the invasive Asian ambrosia beetle Euwallacea validis (Coleoptera, Scolytinae, Xyleborini) and from the galleries that females had constructed in dying Ailanthus altissima (tree-of-heaven) symptomatic for Verticillium wilt in south-central Pennsylvania, USA. This ambrosia fungus was cultivated by Euwallacea validis as the primary source of nutrition together with a second symbiont, Raffaelea subfusca . Female beetles transport their fungal symbionts within and from their natal galleries in paired pre-oral mycangia. Fusarium oligoseptatum was distinguished phenotypically from the 11 other known members of the Ambrosia Fusarium Clade (AFC) by uniquely producing mostly 1-2 septate clavate sporodochial conidia that were swollen apically. Phylogenetic analysis of multilocus DNA sequence data resolved F. oligoseptatum as a genealogically exclusive species-level lineage but evolutionary relationships with other members of the AFC were unresolved. Published studies have shown that F. oligoseptatum can be identified via phylogenetic analysis of multilocus DNA sequence data or a PCR multiplex assay employing species-specific oligonucleotide primers. In addition, to provide nomenclatural stability, an epitype was prepared from an authentic strain of F. ambrosium that was originally isolated from a gallery constructed in Chinese tea (Camellia sinensis ) by E. fornicatus in India, together with its lectotypification based on a published illustration.

Cryptic genetic variation in an inbreeding and cosmopolitan pest, Xylosandrus crassiusculus, revealed using ddRADseq.

Each year new exotic species are transported across the world through global commerce, causing considerable economic and ecological damage. An important component of managing invasion pathways is to identify source populations. Some of the most widespread exotic species are haplodiploid ambrosia beetles. The ability to mate with siblings (inbreed) and their transportable food source (symbiotic fungus) have enabled them to colonize most of the world and become pests of plant nurseries, lumber, and forests. One of the fastest spreading ambrosia beetles is Xylosandrus crassiusculus. In order to discover the source populations of this globally invasive species, track its movement around the world, and test biogeographical scenarios, we combined restriction site‐associated DNA sequencing (RADseq) with comprehensive sampling across the species native and introduced range. From 1,365 genotyped SNP loci across 198 individuals, we determined that in its native range, X. crassiusculus is comprised of a population in Southeast Asia that includes mainland China, Thailand, and Taiwan, and a second island population in Japan. North America and Central America were colonized from the island populations, while Africa and Oceania were colonized from the mainland Asia, and Hawaii was colonized by both populations. Populations of X. crassiusculus in North America were genetically diverse and highly structured, suggesting (1) numerous, repeated introductions; (2) introduction of a large founding population; or (3) both scenarios with higher than expected outcrossing. X. crassiusculus, other wood‐boring insects, and indeed many other pests with unusual genetic structure continue to spread around the world. We show that contemporary genetic methods offer a powerful tool for understanding and preventing pathways of future biosecurity threats.

Interaction of Insecticide and Media Moisture on Ambrosia Beetle (Coleoptera: Curculionidae) Attacks on Selected Ornamental Trees.

Exotic ambrosia beetles, particularly Xylosandrus crassiusculus (Motschulsky) (Coleoptera: Curculionidae: Scolytinae) and Xylosandrus germanus (Blandford) (Coleoptera: Curculionidae: Scolytinae), are among the most damaging pests of ornamental trees in nurseries. Growers have had few tactics besides insecticide applications to reduce ambrosia beetle attacks but recent research has shown that attacks may be reduced by maintaining media moisture below a 50% threshold thereby reducing flood stress. We compared the efficacy of managing media moisture and insecticide applications for reducing ambrosia beetle attacks on three ornamental tree species in North Carolina. During trials in spring 2013 and 2015, flooded Cornus florida and Cornus kousa were heavily attacked despite sprays with permethrin, but nonflooded C. kousa or C. florida were not attacked. In spring 2015 trials, both nonflooded and flooded Styrax japonicus were heavily attacked regardless of permethrin applications. Although ethanol emissions were not measured, the apparently healthy nonflooded S. japonicus trees may have been exposed to an unknown physiological stress, such as low temperature injury, the previous winter, which predisposed them to beetle attack. However, ethanol levels within host tissues were not measured as part of the current study. X. crassiusculus (75%), Xyloborinus saxesenii Ratzburg (13%), and X. germanus (9%) were the most abundant species collected in ethanol baited traps deployed in 2015, while X. crassiusculus (63%) and X. germanus (36%) were the predominant species reared from attacked trees. Results indicate that managing media moisture levels at or below 50%, and maximizing tree health overall, may provide significant protection against Xylosandrus spp. attacks in flood intolerant tree species.

Nutritional symbionts of a putative vector, Xyleborus bispinatus, of the laurel wilt pathogen of avocado, Raffaelea lauricola

Ambrosia beetles subsist on fungal symbionts that they carry to, and cultivate in, their natal galleries. These symbionts are usually saprobes, but some are phytopathogens. Very few ambrosial symbioses have been studied closely, and little is known about roles that phytopathogenic symbionts play in the life cycles of these beetles. One of the latter symbionts, Raffaelea lauricola, causes laurel wilt of avocado, Persea americana, but its original ambrosia beetle partner, Xyleborus glabratus, plays an uncertain role in this pathosystem. We examined the response of a putative, alternative vector of R. lauricola, Xyleborus bispinatus, to artificial diets of R. lauricola and other ambrosia fungi. Newly eclosed, unfertilized females of X. bispinatus were reared in no-choice assays on one of five different symbionts or no symbiont. Xyleborus bispinatus developed successfully on R. lauricola, R. arxii, R. subalba and R. subfusca, all of which had been previously recovered from field-collected females of X. bispinatus. However, no development was observed in the absence of a symbiont or on another symbiont, Ambrosiella roeperi, recovered from another ambrosia beetle, Xylosandrus crassiusculus. In the no-choice assays, mycangia of foundress females of X. bispinatus harbored significant colony-forming units of, and natal galleries that they produced were colonized with, the respective Raffaelea symbionts; with each of these fungi, reproduction, fecundity and survival of the beetle were positively impacted. However, no fungus was recovered from, and reproduction did not occur on, the A. roeperi and no symbiont diets. These results highlight the flexible nature of the ambrosial symbiosis, which for X. bispinatus includes a fungus with which it has no evolutionary history. Although the “primary” symbiont of the neotropical X. bispinatus is unclear, it is not the Asian R. lauricola.

First record of the Granulate Ambrosia Beetle, Xylosandrus crassiusculus(Coleoptera: Curculionidae, Scolytinae), in the Iberian Peninsula.

The Granulate Ambrosia Beetle Xylosandrus crassiusculus, an alien species of Asian origin, was recorded for first time in the Iberian Peninsula. Many specimens were collected in October 2016 in the Valencia region (Spain) from infested carob trees. The species is included in the EPPO Alert List as causing serious damage in many Mediterranean regions. A key for the morphological identification of the Xylosandrus species occurring in Europe is also reported.

Development of Microsatellites for Population Genetic Analyses of the Granulate Ambrosia Beetle (Coleoptera: Curculionidae).

Limited male dispersal and local mating in ambrosia beetles are expected to result in extreme inbreeding and highly structured populations. In this study, we developed microsatellite markers for the granulate ambrosia beetle, Xylosandrus crassiusculus (Motschulsky), for use in future studies into population and family structure of this invasive pest species. We employed de novo next-generation sequencing to generate whole genome shotgun sequences for the characterization of microsatellite loci. Approximately 6% of the 84,024 contigs generated from Hi-Seq Illumina 2x250bp sequencing contained microsatellites with at least four repeats of di-, tri-, tetra-, penta-, and hexamers. Primers were synthesized for 40 microsatellite loci with trimer repeat units. Twenty-four primer pairs yielded consistent PCR products of unique loci and were validated for population genetic application using three sample groups each containing 20 X. crassiusculus individuals from Mississippi. Thirteen loci were found to be polymorphic with up to five alleles per population. The two beetle sample groups from Pearl River County (Poplarville and McNeill) belonged genetically to the same population. The population from Lamar County (Purvis) was genetically distinct, separated by a moderate genetic distance (FST = 0.11) and five unique alleles (with >5% frequency). Consistent with the perceived mating structure (incest of females with flightless males), the populations showed homozygote excess at most loci, as indicated by the coefficients of inbreeding (FIT = 0.45 and FIS = 0.37) and high mean relatedness among individuals (r = 0.15).

Laurel Wilt in Natural and Agricultural Ecosystems: Understanding the Drivers and Scales of Complex Pathosystems

Laurel wilt kills members of the Lauraceae plant family in the southeastern United States. It is caused by Raffaelea lauricola T.C. Harr., Fraedrich and Aghayeva, a nutritional fungal symbiont of an invasive Asian ambrosia beetle, Xyleborus glabratus Eichhoff, which was detected in Port Wentworth, Georgia, in 2002. The beetle is the primary vector of R. lauricola in forests along the southeastern coastal plain of the United States, but other ambrosia beetle species that obtained the pathogen after the initial introduction may play a role in the avocado (Persea americana Miller) pathosystem. Susceptible taxa are naïve (new-encounter) hosts that originated outside Asia. In the southeastern United States, over 300 million trees of redbay (P. borbonia (L.) Spreng.) have been lost, and other North American endemics, non-Asian ornamentals and avocado—an important crop that originated in MesoAmerica—are also affected. However, there are no reports of laurel wilt on the significant number of lauraceous endemics that occur in the Asian homeland of R. lauricola and X. glabratus; coevolved resistance to the disease in the region has been hypothesized. The rapid spread of laurel wilt in the United States is due to an efficient vector, X. glabratus, and the movement of wood infested with the insect and pathogen. These factors, the absence of fully resistant genotypes, and the paucity of effective control measures severely constrain the disease’s management in forest ecosystems and avocado production areas.

Management of laurel wilt of avocado, caused by Raffaelea lauricola

Laurel wilt is caused by Raffaelea lauricola, a nutritional symbiont of an Asian ambrosia beetle, Xyleborus glabratus. American members of the Lauraceae plant family are most susceptible and 300 million trees have been killed by the disease in the southeastern USA since 2003. Recently, commercial production of an important crop in the laurel family, avocado (Persea americana), has been affected in southern Florida. We summarize studies in which diverse measures were tested for managing the disease. In all studies, trees were treated with potential laurel wilt control measures and subsequently inoculated with R. lauricola. On potted plants in greenhouse experiments, commercial nutritional products (Greenstim and Keyplex 350) and SAR products (Agri-Fos and Nutri-Phite), when applied as soil drenches or foliar sprays, had either no impact on, or increased laurel wilt symptom development compared to non-treated control treatments. Bark applications of Tilt (a propiconazole fungicide for which emergency registration had been obtained in 2010) in a surfactant (Pentrabark) enabled significant laurel wilt protection in greenhouse studies on small potted plants, but Pentrabark and other surfactants moved little propiconazole into the xylem of fruit-bearing trees in field studies. In efficacy studies in the field, Propiconazole Pro (an injectable formulation of propiconazole), Tilt, and two experimental formulations of another triazole fungicide, tebuconazole, decreased the development of laurel wilt compared to nontreated control trees when applied as undiluted injections into branches and scaffold limbs (microinjection), or injection of dilute fungicide into tree flare roots (macroinfusion). However, symptoms developed in all treated trees by 10–11 months after inoculation with R. lauricola, indicating that trees would need to be re-treated at least on an annual basis. Regardless of how fungicides were applied, insignificant levels of different active ingredients entered fruit. Although fungicide treatment of fruit-bearing avocado trees is not a concern for food safety and several triazole and DMI fungicides can protect avocado trees from laurel wilt, cost-effective measures with which the xylem could be loaded with and protected by these products remains a challenge. Management of laurel wilt in commercial avocado production areas is discussed.

Comparative Morphology and Distribution of Antennal Sensilla onXylosandrus germanusandXylosandrus crassiusculus(Coleoptera: Curculionidae: Scolytinae)

The nonnative ambrosia beetles Xylosandrus germanus (Blandford) and Xylosandrus crassiusculus (Motschulsky) are destructive pests of plants and trees growing in ornamental nurseries and tree fruit orchards. Perception of stress-induced volatiles plays an important role in aiding female X. germanus and X. crassiusculus in locating vulnerable hosts, while adult males of both species are flightless and not involved in host selection. Scanning electron microscopy was used to characterize the antennae of both species, which consisted of a scape, funicle, and club. Emphasis was placed on the type, structure, and distribution of sensilla associated with the antennal clubs of female and male X. germanus and X. crassiusculus . Sensilla observed on the anterior surface of the club for females and males of both species include one type of sensillum chaeticum (SC1), one type of sensillum trichodeum (ST1), and five types of sensilla basiconica (SB1–5). Sensilla are distributed in association with two sensory bands and/or a basal cluster. SB1, the most abundant sensilla type found on female and male clubs for both species, appears to be highly porous. No obvious sexual dimorphism was observed regarding sensilla type, but most types are more abundant on the antennal clubs of females compared with males for X. germanus and X. crassiusculus . Possible functions of the sensilla types are discussed based on morphology. These results provide an improved understanding of sensilla associated with X. germanus and X. crassiusculus that will aid electrophysiological investigations into their host selection behavior.

Competition between biological control fungi and fungal symbionts of ambrosia beetles Xylosandrus crassiusculus and X. germanus (Coleoptera: Curculionidae): Mycelial interactions and impact on beetle brood production

Ambrosia beetles Xylosandrus crassiusculus and X. germanus are among the most important exotic pests of orchards and nurseries in the US and are difficult to control using conventional insecticides because of their cryptic habits. The use of biological control agents may prove effective by targeting both beetles and fungal symbionts inside tree galleries: entomopathogenic fungi could be used to target beetle foundresses and their brood, or mycoparasitic fungi, e.g., Trichoderma harzianum, could be used to target their associated fungal symbionts. We used a combination of in vitro assays and beetle bioassays to examine competition between symbionts and biological control fungi and the impact of biological control fungi on beetle brood production. The in vitro assays showed T. harzianum outcompeted different strains of Ambrosiella roeperi and A. grosmanniae associated with X. crassiusculus and X. germanus, respectively, whether in primary or secondary resource capture assays. In contrast, entomopathogenic fungi Beauveria bassiana and Metarhizium brunneum blocked the spread of symbionts only in primary competition assays. Complementary beetle bioassays showed that beetle galleries in T. harzianum-treated beech stems had sparse symbiont growth, many with no or only a small number of eggs present. Brood numbers produced by foundresses in T. harzianum-treated stems were comparable to those in stems treated with either entomopathogen at the higher dosages, in which brood reduction was likely due to foundress mortality prior to laying eggs or after laying only a small number of eggs. These results show the potential of using biological control fungi in targeting ambrosia beetle populations either directly by killing foundresses and reducing brood production or indirectly by suppressing symbiont growth in their galleries.

Survey of Twig-Inhabiting Coleoptera in Louisiana, USA

Abstract Twigs are an understudied habitat utilized by many beetle species. Samples of twigs were collected in all six Level III Ecoregions in Louisiana during April and May 2013. The twigs were maintained in emergence chambers from which 942 specimens of adult Coleoptera were obtained, representing 31 families, 111 genera, and 128 species. Beetle richness and composition were not significantly different among ecoregions. Three species collected represent new state records: Pseudochoragus nitens (LeConte) (Anthribidae); Dryotribus mimeticus Horn (Curculionidae); and Narthecius grandiceps LeConte (Laemophloeidae). Four non-native species, all Curculionidae, were collected: Cyrtepistomus castaneus (Roelofs) (Entiminae); Cnestus mutilatus (Blandford) (Scolytinae); Xylosandrus crassiusculus (Motschulsky) (Scolytinae); and Xylosandrus germanus (Blandford) (Scolytinae).

Developing a Media Moisture Threshold for Nurseries to Reduce Tree Stress and Ambrosia Beetle Attacks.

Exotic ambrosia beetles are among the most damaging pests of trees grown in nurseries. The primary pests Xylosandrus crassiusculus Motschulsky and Xylosandrus germanus Blandford use ethanol to locate vulnerable trees. Research, primarily with X. germanus, has shown that flood-stressed trees emit ethanol and are preferentially attacked by ambrosia beetles. Our goal was to develop a media (also called potting soil) moisture threshold as an integrated pest management (IPM) tactic and assess grower practices that lead to ambrosia beetle attacks. Flooded Cornus florida L., Cornus kousa Burg., and Magnolia grandiflora L. trees incurred more attacks than unflooded trees that were not attacked. To determine optimal media moisture levels, we grew flood-tolerant Acer rubrum L. and flood-intolerant C. florida in containers with 10, 30, 50, 70, or 90% media moisture. No flooded or unflooded A. rubrum were attacked. However, C. florida grown in 70 or 90% moisture were attacked and died, whereas trees at 30 and 50% moisture were not attacked. Thus, we suggest an upper moisture threshold of 50% when growing C. florida and other flood-intolerant trees. However, during peak ambrosia beetle flight activity in spring 2013 and 2014, we found that media moisture levels in commercial nurseries were often between 50 and 90%. Implementing a media moisture threshold, as a new IPM tool, could reduce ambrosia beetle attacks and the need for insecticide applications, which is currently the only available management tactic. Future research should focus on how changes in substrates, irrigation, and other practices could help growers meet this threshold.

Redbay Survival Eleven Years after Infection with an Exotic Disease on St. Catherines Island, Georgia, USA

<p class="1Body">Introduced to the United States in 2002, laurel wilt (<em>Raffaelea lauricola</em>) is a fungus that causes life threatening defensive responses in the vascular system of trees within the Lauraceae family, and it is introduced to the tree by the Asian ambrosia beetle (<em>Xyleborus glabratus)</em>. Redbay (<em>Persea borbonia)</em> is the preferred host species within the US coastal plains and maritime forests, and it has experienced rapid mortality throughout its range in the southeastern United States since the introduction of the ambrosia beetle and associated fungus. In this study, we inventoried all dead and live redbay trees from replicated transects inside a maritime forest, a successional old-field forest (both located on the island’s Pleistocene core), and a Holocene hammock to examine the role of soils, prior land use and landscape position on redbay survival eleven years after the introduction of the exotic beetle and fungus on the island. Results indicated that the maritime forest had a significantly higher number of redbay trees prior to infection compared to the hammock or old-field sites. Eleven years post-infection, all three sites had similar densities of redbay trees and the surviving trees had similar diameter distributions among the three sites. Soils under the maritime forest had significantly higher phosphorous (P) and pH concentrations, and the Holocene hammock had a higher water table compared to the sites on the Pleistocene core. Almost all living trees at each site had signs of invertebrate herbivory and twig borer damage. Prior land use history and soils affected redbay densities before laurel wilt infection, but eleven years post-infection, all three site types had similar redbay densities, diameters, basal areas, and levels of herbivory and surviving trees did not demonstrate signs of photosynthetic stress.</p>

Tea Shot-Hole Borer Euwallacea fornicatus (Eichhoff, 1868) (Insecta: Coleoptera: Curculionidae: Scolytinae)

The tea shot-hole borer is an Asian ambrosia beetle introduced to Florida in the early 2000s. In Florida it does not have any known economic impact, but it is a serious pest of tea around the world and is one of the few ambrosia beetles that can infest healthy plants. The tea shot hole borer has a symbiotic relationships with the ambrosia fungus Fusarium ambrosium (Gadd & Loos), which is also a weak plant pathogen. This 4-page fact sheet includes a diagnosis section with guidance for avoiding misidentification. Written by You Li, Andrea Lucky, and Jiri Hulcr, and published by the UF Department of Entomology and Nematology, June 2015.