Laurel Wilt Research Articles

Temporal Analysis of Sesquiterpene Emissions From Manuka and Phoebe Oil Lures and Efficacy for Attraction of Xyleborus glabratus (Coleoptera: Curculionidae: Scolytinae)

Redbay ambrosia beetle, Xyleborus glabratus Eichhoff, is an exotic wood-borer that vectors the fungal agent (Raffaelea lauricola) responsible for laurel wilt. Laurel wilt has had severe impact on forest ecosystems in the southeastern United States, killing a large proportion of native Persea trees, particularly redbay (P. borbonia) and swampbay (P. palustris), and currently poses an economic threat to avocado (P. americana) in Florida. To control the spread of this lethal disease, effective attractants are needed for early detection of the vector. Two 12-wk field tests were conducted in Florida to evaluate efficacy and longevity of manuka and phoebe oil lures, and to relate captures of X. glabratus to release rates of putative sesquiterpene attractants. Two trap types were also evaluated, Lindgren funnel traps and sticky panel traps. To document lure emissions over time, a separate set of lures was aged outdoors for 12 wk and sampled periodically to quantify volatile sesquiterpenes using super-Q adsorbant and gas chromatography-mass spectroscopy analysis. Phoebe lures captured significantly more X. glabratus than manuka lures, and sticky traps captured more beetles than funnel traps. Phoebe lures captured X. glabratus for 10-12 wk, but field life of manuka lures was 2-3 wk. Emissions of alpha-copaene, alpha-humulene, and cadinene were consistently higher from phoebe lures, particularly during the 2-3 wk window when manuka lures lost efficacy, suggesting that these sesquiterpenes are primary kairomones used by host-seeking females. Results indicate that the current monitoring system is suboptimal for early detection of X. glabratus because of rapid depletion of sesquiterpenes from manuka lures.

Assessing the Survival of the Redbay Ambrosia Beetle and Laurel Wilt Pathogen in Wood Chips

What is the best way for homeowners to dispose of dead redbay trees to avoid spreading laurel wilt? This 4-page fact sheet summarizes a UF/IFAS study providing evidence that a simple technique — chipping the dead trees — can help contain the disease within a small area and that there is a low probability of long-distance movement of LW via wood chips. Written by Don Spence, Jason Smith, Albert Mayfield III, Jiri Huler, Randy Ploetz, and Lukasz Stelinski, and published by the UF Department of School of Forest Resources and Conservation, November 2011. Reviewed August 2014.

Impact of laurel wilt, caused by Raffaelea lauricola, on xylem function in avocado, Persea americana

SummaryLaurel wilt, caused by Raffaelea lauricola, is a lethal, vascular disease of avocado, Persea americana. Its impact on xylem function was examined in artificially inoculated plants of the ‘Simmonds’ cultivar. Three, 7, 14, 21 and 42 days after inoculation (dai), plants were rated externally and internally for disease severity on a subjective one (asymptomatic) to 10 (dead or 100% symptomatic) scale. Stems were then cut under water, 15 cm below the inoculation point, and placed in 0.1% aqueous solutions of acid fuschin in a greenhouse. After 48 h, the percentage of functional xylem was estimated 10 and 5 cm above and below the inoculation point by quantifying acid fuschin‐stained portions of digitized stem cross‐sections. Hydraulic conductivity was determined by placing the proximal end of 5‐cm‐long stem sections, harvested between 5 and 10 cm above the inoculation point, in water and quantifying the volume of water that was drawn over time through the distal end under partial pressure (350 mm Hg). Functional xylem decreased by 3 dai, well before the development of vascular discoloration (7 dai) and wilting of foliage (14 dai). By 14 dai, extensive vascular discoloration had developed and there was a dramatic reduction in functional xylem; plants with internal disease severities of 7 or greater had <20% functional xylem. Hydraulic conductivity decreased exponentially as non‐functional xylem and disease severity increased. In plants with internal severities >7, mean flow rates of water were 0.07 ml−1 min−1 cm−2vs. 42 ml−1 min−1 cm−2 in mock‐inoculated plants. The rapid development of these changes suggests that it may be difficult to manage laurel wilt in avocado once plants are infected by R. lauricola. Better understanding of the temporal and spatial development of infection and how the host responds to infection may assist efforts to select laurel wilt‐tolerant avocado cultivars.

Laurel Wilt, Caused by Raffaelea lauricola, is Confirmed in Miami-Dade County, Center of Florida's Commercial Avocado Production.

Laurel wilt, caused by Raffaelea lauricola, threatens native and nonnative species in the Lauraceae in the southeastern United States, including the important commercial crop, avocado, Persea americana (2,4). Although the pathogen's vector, Xyleborus glabratus, was detected in Miami-Dade County, FL in January 2010, laurel wilt had not been reported (4). In February 2011, symptoms of the disease were observed on native swampbay, P. palustris, in Miami-Dade County (25°72'N, 80°48'W). Externally, foliage was brown, necrotic, and did not abscise; internally, sapwood was streaked with dark gray-to-bluish discoloration; and, in dead trees, holes of natal galleries of the vector from which columns of frass were attached were evident. On a semiselective medium for R. lauricola, a fungus with the pathogen's phenotype was isolated from symptomatic sapwood. Colonies were slow growing, light cream in color, with dendritic, closely appressed mycelium and often a slimy surface. A representative strain of the fungus was further identified with PCR primers for diagnostic small subunit (SSU) rDNA (1) and its SSU sequence (100% match, GenBank Accession No. JN578863). In each of two experiments, plants of 'Simmonds' avocado, the most important cultivar in Florida, were inoculated with three strains of the fungus, as described previously (3). Symptoms of laurel wilt developed in all inoculated plants and the fungus was recovered from each. After aerial and further ground surveys, additional symptomatic swampbay trees, some of which had defoliated, were detected in the vicinity of the original site. Since swampbay defoliates only a year or more after symptoms develop (4), the 2010 detection of X. glabratus may have coincided with an undetected presence of the disease. As of July 2011, a 6-km-diameter disease focus was evident in the area, the southernmost edge of which is 5 km from the nearest commercial avocado orchard. In August 2011, a dooryard avocado tree immediately north of the above focus was affected by laurel wilt, and an SSU sequence confirmed the involvement of R. lauricola (GenBank Accession No. JN613280). The outbreak of laurel wilt in Miami-Dade County represents a 150 km southerly jump in the distribution of this disease in the United States ( http://www.fs.fed.us/r8/foresthealth/laurelwilt/dist_map.shtml ) and is the first time this disease has been found in close proximity to Florida's primary commercial avocado production area. Approximately 98% of the state's commercial avocados, worth nearly $54 million per year, are produced in Miami-Dade County. Since effective fungicidal and insecticidal measures have not been developed for large, fruit-bearing trees, mitigation efforts will focus on the rapid identification and destruction of infected trees (3,4).

First Report of Laurel Wilt Disease Caused by Raffaelea lauricola on Pondspice in Florida.

Laurel wilt is a fungal vascular disease of redbay (Persea borbonia (L.) Spreng) and other plants in the family Lauraceae in the southeastern United States (1). The disease is caused by Raffaelea lauricola T. C. Harr., Fraedrich & Aghayeva, which is vectored by the exotic redbay ambrosia beetle (Xyleborus glabratus Eichhoff) (2). Pondspice (Litsea aestivalis (L.) Fern.) is an obligate wetland shrub listed as endangered in Florida and Maryland and threatened in Georgia (4). On 29 August 2008, 369 of 430 (85%) pondspice trees observed at St. Marks Pond in St. John's County, Florida were dead and/or dying (4). Stem samples were collected from plants with wilted and reddened foliage, entrance holes with boring dust characteristic of ambrosia beetle attack, and dark discoloration in the outer sapwood. Discolored stem sections were surface disinfested for 30 s in a 5% sodium hypochlorite solution and then plated onto cycloheximide streptomycin malt extract agar (1). Smooth, cream-buff, submerge hyphae with uneven margins resembling R. lauricola (2) was observed growing from all sapwood pieces. DNA was extracted from a single isolate (PL 392) and the 18s small subunit rDNA was PCR amplified and sequenced with primers NS1 and NS4 (3), resulting in a 1,026-bp amplicon. A BLASTn search showed identical homology to R. lauricola strain PL 159 (GenBank Accession No. EU257806). The 18s small subunit rDNA sequence was deposited into GenBank (FJ514097). In May 2011, a spore suspension was made by flooding a single-spore culture plate of isolate PL 392 with 2 ml of sterile water, collecting the spores by pipette, and quantification by hemacyometer to 1.5 × 106 spores/ml. Pathogenicity tests were conducted on 1 to 1.5 m tall pondspice plants. Six saplings were wounded by a 3/32-inch drill bit, with four receiving 50 μl of the spore suspension and two serving as water-inoculated controls. All plants were kept in a greenhouse under ambient temperature. Within 21 days, all fungal-inoculated saplings displayed complete canopy wilt, typical of laurel wilt. R. lauricola was later recovered from all four infected plants, completing Koch's postulates. To determine if the vector can reproduce in pondspice, infected stem sections were placed in a plastic rearing box indoors at room temperature, and both callow and mature adult female X. glabratus emerged in October and November 2008. Although laurel wilt has been previously observed on pondspice in South Carolina and Georgia (1), this is the first confirmation of the disease on pondspice in Florida and the first confirmation of the vector from stem material of this host.

The Scent of a Partner: Ambrosia Beetles Are Attracted to Volatiles from Their Fungal Symbionts

Invasive fungus-growing ambrosia beetles are an emerging threat to forest ecosystems and fruit industries, but management tools are lacking. Here we explored the potential of beetle symbionts-ambrosia fungi-as a source of attractants. Our focus was the redbay ambrosia beetle, Xyleborus glabratus, and its symbiotic fungus, Raffaelea lauricola, which are devastating lauraceous hosts in the southeastern United States. We also tested three additional co-occurring beetle species and their symbionts. Each beetle species was consistently attracted to the odors of its symbiotic fungal species, occasionally also to symbionts of other species, but never to non-symbiotic Trichoderma. We further confirmed attraction to ethanol (positive control) in some species. Thus, ambrosia fungi produce volatiles attractive to their vector beetles, which may have potential as novel lures for ambrosia beetle management.

Chemical Control of the Redbay Ambrosia Beetle,Xyleborus glabratus, and Other Scolytinae (Coleoptera: Curculionidae)

ABSTRACT The redbay ambrosia beetle (RAB), Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae), is an adventive pest of Lauraceae in the southeastern U.S. This wood-boring insect vectors a lethal fungus, Raffaelea lauricola T. C. Harr., Fraedrich & Aghayeva, the causal agent of laurel wilt (LW) disease. The vector-pathogen complex is responsible for extensive mortality of native Persea trees in South Carolina, Georgia, and northern Florida, and now poses an imminent threat to the avocado (Persea americana Mill.) industry in south Florida. While chemical control of the vector is not viewed as the primary solution, control tactics should be made available to Florida avocado growers. Field and laboratory tests were conducted using avocado bolts, potted avocado trees, and field grown swampbay trees (Persea palustris (Raf.) Sarg.) treated with contact and systemic insecticides. Zeta-cypermethrin + bifenthrin and lambda-cyhalothrin + thiamethoxam provided the most consistent control of Scolytin...

Comparative Analysis of Terpenoid Emissions from Florida Host Trees of the Redbay Ambrosia Beetle,Xyleborus glabratus(Coleoptera: Curculionidae: Scolytinae)

ABSTRACT The redbay ambrosia beetle, Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae), is an exotic wood-boring insect that vectors Raffaelea lauricola, the fungal pathogen responsible for laurel wilt, a lethal disease of trees in the Lauraceae. First detected in the U.S. near Savannah, GA in 2002, X. glabratus has since spread throughout the southeastern coastal plain causing high mortality in native Persea species, particularly redbay (P. borbonia) and swampbay (P. palustris). Currently, breeding populations of X. glabratus pose an imminent threat to the avocado (P. americana) industry in south Florida. There is a critical need for effective attractants to detect, monitor, and control the spread of this invasive pest. In an effort to identify host-based attractants for dispersing female X. glabratus, we conducted a comparative study of the volatile chemicals emitted from wood of six species of Lauraceae found in Florida: avocado (Persea americana), redbay (P. borbonia), swampbay (P. ...

Responses of avocado to laurel wilt, caused byRaffaelea lauricola

Laurel wilt, caused byRaffaelea lauricola, threatens native and non‐native species in the Lauraceae in the south‐eastern USA. Avocado,Persea americana, is the most important agricultural suscept of laurel wilt. Grafted plants (clonal scions on seedling rootstocks) of 24 cultivars were screened against the disease in the field from 2008 to 2010. Disease was induced with either mycelial plugs or conidial suspensions ofR. lauricola. There were significant differences in the severity of disease that developed on different cultivars, and West Indian cultivars were most susceptible (P < 0·05). Simmonds, a West Indian cultivar that comprises 35% of the commercial production in Florida, was consistently susceptible and was used as a standard genotype in different studies. Disease severity increased significantly on cv. Simmonds as plant size (stem diameter) increased (P < 0·0042). In greenhouse studies, internal (sapwood) and external disease severities on cv. Simmonds were correlated (P < 0·0001), and a threshold was evident, in that external symptoms developed only after moderately severe symptoms had developed internally. Latent infection was uncommon;R. lauricolawas usually isolated on a semiselective medium or detected via qPCR only from discoloured xylem of inoculated cv. Simmonds. As basipetal movement of the pathogen was common, its movement among trees via root grafts is probable. Greater understanding is needed of the movement ofR. lauricolain naturally and artificially infected trees, and whether sufficient tolerance exists in avocado to assist in the management of this important new disease.

First Report of Laurel Wilt Caused by Raffaelea lauricola on Sassafras in Mississippi.

Laurel wilt is caused by the fungus Raffaelea lauricola T.C. Harrin., Aghayeva & Fraedrich and is lethal to redbay (Persea borbonia (L.) Spreng.), sassafras (Sassafras albidum (Nutt.) Nees), and other species in the Lauraceae (1). The fungus is carried by the redbay ambrosia beetle (Xyleborus glabratus Eichh.), which is native to Asia. After being discovered in Georgia in 2002 (1), X. glabratus and R. lauricola have spread rapidly, causing extensive redbay mortality in South Carolina, Georgia, Florida, and Mississippi (1,4). The disease has also been confirmed on sassafras in Florida, South Carolina (1), and Georgia. Questions remain as to whether laurel wilt will continue to spread on sassafras, which often occurs as scattered trees in the eastern United States. In June 2010, a homeowner reported that a sassafras tree north of Van Cleave, MS (30.668°N, 88.686°W) had begun wilting in late May. This landscape tree had three 10-m high stems (~20 cm in diameter at breast height). Dark staining in the xylem was observed around the entire circumference of all three stems and nearly all leaves were bronze colored and wilted. No ambrosia beetle tunnels were observed in the stems. No other symptomatic Lauraceae were encountered in the wooded area within 300 m. The nearest known location with laurel wilt on redbay was ~15 km away (4). A Lindgren funnel trap baited with manuka oil (2) was placed at the site in June and monitored biweekly until November, but no X. glabratus adults were captured. Chips from discolored xylem of the sassafras were surface sterilized, plated on cycloheximide-streptomycin malt agar, and R. lauricola was readily isolated (1). Identity of the fungus (isolate C2792 in collection of T. Harrington) was confirmed by using partial sequences of the 28S rDNA (3). The sassafras sequence was identical to that of all known sequences of R. lauricola in the United States, including GenBank No. EU123076 (the holotype isolate from redbay). To confirm pathogenicity, isolate C2792 was grown on malt extract agar and three redbay (average: 141 cm high and 12 mm in diameter at soil interface) and three sassafras (average: 170 cm high and 17 mm in diameter at soil interface) potted plants were wound inoculated with 0.2 ml of a spore suspension (4.9 × 106 conidia/ml) (1). Three control plants of each species were inoculated with sterile deionized water. After 8 weeks in a growth chamber at 26°C, all inoculated redbay and sassafras plants exhibited xylem discoloration above and below the inoculation point, two of the redbay and two of the sassafras had died, and the other plant of each species exhibited partial wilt (the main terminal or one or more branches). All control plants were asymptomatic. R. lauricola was reisolated from all inoculated symptomatic plants but not from controls. To our knowledge, this is the first report of laurel wilt on sassafras in Mississippi. Both redbay (4) and sassafras appear to be highly susceptible to the disease as it moves westward. Sassafras is less attractive than redbay to X. glabratus and it was thought that this might contribute to slowing the spread of laurel wilt once outside the range of redbay (2). Nonetheless, our observations confirm that sassafras can be infected where laurel wilt on redbay is not in the immediate vicinity.

Impact of Systemic Fungicides on Lesions Formed by Inoculation with the Bluestain Fungus (Ophiostoma minus) in Loblolly Pine (Pinus taeda L.)

Ophiostomatoid fungi are important components within the highly damaging insect-fungal complexes attacking trees in North America. This group includes the disease agents responsible for Dutch elm disease and laurel wilt, as well as a number of associates of tree-killing bark beetles. While systemic fungicides have been applied against ophiostomatoids in certain fungus-host systems, the breadth of their utility and their management implications for a wide array of fungus and host species remain uncertain. To evaluate the impact of commercially available fungicides against the bluestaining fungus Ophiostoma minus, an associate of the southern pine beetle, researchers conducted two experiments with loblolly pines (Pinus taeda; mean dbh 14.2 and 18.5 cm, respectively) in central Louisiana, U.S. The first experiment screened three fungicides (Alamo®, Arbotect® 20-S, and PHOSPHO-jet) for their systemic impacts on O. minus, and the second further evaluated the best performing product (Alamo) alone and in combination with Arbotect 20-S. In all cases, loblolly pines were stem-injected basally and challenged with inoculations of cultured O. minus at time periods ranging from 28 days to 738 days post-treatment. In both experiments, treatment of loblolly pines with Alamo produced the smallest lesion areas, indicating that this treatment was the most effective for limiting the within-tree growth of O. minus. This effect was still present more than two years post-treatment. The study authors conclude that Alamo is the most effective product of those evaluated for prophylactic treatment against O. minus, and suggest that evidence is building for the effectiveness of this product generally against ophiostomatoid fungi.

Susceptibility to Laurel Wilt and Disease Incidence in Two Rare Plant Species, Pondberry and Pondspice.

Laurel wilt, caused by Raffaelea lauricola, has been responsible for extensive losses of redbay (Persea borbonia) in South Carolina and Georgia since 2003. Symptoms of the disease have been noted in other species of the Lauraceae such as the federally endangered pondberry (Lindera melissifolia) and the threatened pondspice (Litsea aestivalis). Pondberry and pondspice seedlings were inoculated with R. lauricola from redbay, and both species proved highly susceptible to laurel wilt. Field assessments found substantial mortality of pondberry and pondspice, but in many cases the losses were not attributable to laurel wilt. R. lauricola was isolated from only 4 of 29 symptomatic pondberry plants at one site, but the fungus was not recovered from three plants at another site. R. lauricola was isolated from one of two symptomatic pondspice plants at one site, and from five of 11 plants at another site, but not from any plant at a third site. Insect bore holes, similar to those produced by Xyleborus glabratus (the vector of laurel wilt), were found in some pondberry and pondspice stems, but adults were not found. Damage caused by Xylosandrus compactus was found in pondberry stems, but this ambrosia beetle does not appear to be a vector of R. lauricola. Xyleborinus saxeseni adults were found in a dying pondspice with laurel wilt, and R. lauricola was recovered from two of three adults. Isolates of R. lauricola from pondberry, pondspice, and X. saxeseni had rDNA sequences that were identical to previously characterized isolates, and inoculation tests confirmed that they were pathogenic to redbay. Because pondberry and pondspice tend to be shrubby plants with small stem diameters, these species may not be frequently attacked by X. glabratus unless in close proximity to larger diameter redbay.

First Report of Raffaelea canadensis Causing Laurel Wilt Disease Symptoms on Avocado in California.

Laurel wilt disease is a newly described vascular disease of redbay (Persea borbonia (L.) Spreng.) and other members of the Lauraceae family in the southeastern United States. The disease, caused by the fungus Raffaelea lauricola and vectored by a nonnative redbay ambrosia beetle (Xyleborus glabratus Eichhoff), was first detected in Georgia in 2003 (1). Laurel wilt has caused extensive mortality of native redbay in Georgia, Florida, South Carolina, and recently, Mississippi. The avocado, Persea americana, is in the Lauraceae family and has been shown to be susceptible to the laurel wilt pathogen in Florida (3). The potential spread of this pathogen into California is of concern to the commercial avocado industry. During a survey in 2010 in a Temecula, CA avocado orchard with a history of root rot, an avocado (cv. Hass) tree with a diameter at breast height (DBH) of 45 cm was found to be showing typical laurel wilt disease symptoms. The crown was approximately 80% declined and exhibited dead branches without leaves. Black-to-brown discolored sapwood under the bark and many ambrosia beetle exit holes within 1 to 1.5 m up the bole were also observed. A Raffaelea sp. was consistently isolated from symptomatic branch tissue (from two different branches) plated onto cycloheximide-streptomycin malt agar (2) and incubated at room temperature for 2 weeks. Small subunit (18S) sequences of rDNA (approximately 1,150 bp) of three Raffaelea isolates were amplified using primers NS1 and NS4 (4) and deposited into GenBank under Accession Nos. JF327799, JF327800, and JF327801. A BLASTn search of all three sequences revealed high homology (98, 99, and 98% respectively) to an accession of R. canadensis associated with a species of ambrosia beetle (GenBank Accession No. AY858665). Pathogenicity testing was conducted by pipetting 50 μl of a 105 conidia per ml suspension of each of two isolates (UCR1080 and UCR1081) into five 2-mm-diameter holes on each of two avocado (cv. Hass) trees (10 to 15 cm DBH). Isolate UCR1080 was inoculated into three holes on Tree 1 and two holes on Tree 2. Isolate UCR1081 was inoculated into two holes on Tree 1 and three holes on Tree 2. Sterile water was used as a control in five 2-mm-diameter holes on each tree. Holes were drilled to the cambium within 1 to 2 m up the bole using a 0.157-cm electric drill. Four months later, phloem tissue was peeled back, lesion lengths were measured, and pieces of necrotic tissue were cultured for completion of Koch's postulates. R. canadensis was consistently reisolated from necrotic tissue but not from control treatments. To our knowledge, this is the first report of R. canadensis associated with wilt on avocado in California. R. canadensis is closely related to R. lauricola, however, its impact on the California avocado industry is unknown at this time.

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.

Toward Fungicidal Management of Laurel Wilt of Avocado.

Laurel wilt threatens commercial and residential production of avocado (Persea americana) in Florida. Laurel wilt on redbay (P. borbonia) was controlled previously with macroinfusions (injections) of Alamo, an injectable formulation of propiconazole. To determine whether Alamo macroinfusion would be cost effective in commercial avocado production, economic analyses were conducted for various macroinfusion scenarios and a standardized production situation in southern Florida. Under prevailing conditions, macroinfusion was not cost effective. In the interest of identifying alternative means to manage the disease, other fungicides and application measures were evaluated. In all, 20 fungicides in 15 chemical groups and 10 fungicide groups were examined in vitro. In vitro inhibition of the radial growth of the pathogen Raffaelea lauricola was determined on fungicide-amended malt extract agar; demethylation inhibitors (DMIs; fenarimol, myclobutanil, propiconazole, prothioconazole, triadimenol, triadimefon, and triticonazole), quinone outside inhibitors (azoxystrobin, pyraclostrobin, and fluoxastrobin), and a quinone inside inhibitor (fluazinam) had the greatest impact on radial growth (the concentration at which growth was reduced by 50% was ≥0.1 μg ml-1). In greenhouse studies, the most inhibitory products in vitro, plus thiabendazole and two products that were not tested in vitro, flutriafol and a potassium salts mixture of phosphorus acid, were tested for disease suppression on artificially inoculated, potted 'Simmonds,' a susceptible avocado cultivar. In general, soil drench applications of the above DMIs and thiabendazole but not azoxystrobin, pyraclostrobin, fluazinam, or the phosphorus acid salt provided significant control of disease (P < 0.05). Topical branch or trunk applications of propiconazole, and triadimenol in 2% Pentrabark, a bark-penetrating surfactant, were also effective at lower rates than were used in drench applications. Comparable levels of disease suppression were achieved when propiconazole was applied at 11% of the rates that were used in soil drenches. Although topical fungicide applications in bark-penetrating surfactants would be a less expensive practice than macroinfusion, moving sufficient concentrations of propiconazole or other fungicides into host xylem will be difficult in trees that are larger than the potted plants that were tested in these trials. Ongoing work examines means by which this goal might be met on fruit-bearing trees in the field.

Attraction of the Redbay Ambrosia Beetle, Xyleborus glabratus, to Avocado, Lychee, and Essential Oil Lures

The redbay ambrosia beetle, Xyleborus glabratus Eichhoff, is an exotic wood-boring insect that vectors the mycopathogen responsible for laurel wilt, a lethal vascular disease of trees in the Lauraceae. High mortality has occurred in native Persea species in the southeastern U.S., and the vector-pathogen complex poses an imminent threat to the production of commercial avocado, P. americana, in south Florida. There is a critical need for effective attractants to detect, monitor, and control this invasive pest. This study combined field tests and laboratory bioassays to evaluate the response of female X. glabratus to host-based volatiles from wood of avocado (cultivars of West Indian, Guatemalan, and Mexican races); from wood of lychee (Litchi chinensis, a presumed non-host that is high in the sesquiterpene α-copaene, a putative attractant); and to commercial lures containing manuka and phoebe oils, two reported attractive baits. Volatile collections and GC-MS analyses were performed to quantify the sesquiterpene content of test substrates. In the field, traps baited with lychee wood captured more beetles than those with wood from avocado cultivars; traps baited with phoebe oil lures captured more beetles than those with manuka oil lures (the current monitoring tool). In field and laboratory tests, X. glabratus did not show a preference among avocado races in either attraction or host acceptance (initiation of boring). In choice tests, lychee was more attractive than avocado initially, but a higher percentage of beetles bored into avocado, suggesting that lychee emits more powerful olfactory/visual cues, but that avocado contains more of the secondary cues necessary for host recognition. Emissions of α-copaene, β-caryophyllene, and α-humulene were correlated with field captures, and lychee wood may be a source of additional semiochemicals for X. glabratus.

Redbay Ambrosia Beetle Xyleborus glabratus Eichhoff (Insecta: Coleoptera: Curculionidae: Scolytinae)

Ambrosia beetles are wood-degrading insects that live in nutritional symbiosis with ambrosia fungi. Usually we consider ambrosia beetles beneficial because they accelerate the decay of dead trees, which is important for nutrient cycling in healthy forests. However, the redbay ambrosia beetle and its fungal symbiont transmit the causal pathogen of laurel wilt disease among plants in the Laurel family (Lauraceae). They are considered a “very high risk” invasive disease pest complex having potential equal to that of Dutch elm disease or chestnut blight. Laurel wilt is a relatively new disease, and much is still unknown about how it will impact the flora of North America. This revised 7-page fact sheet highlights what we do know about this important new pest. Written by Rajinder Mann, Jiri Hulcr, Jorge Peña, and Lukasz Stelinski and published by the UF Department of Entomology and Nematology, May 2011. EENY491/IN886: Redbay Ambrosia Beetle Xyleborus glabratus Eichhoff (Insecta: Coleoptera: Curculionidae: Scolytinae) (ufl.edu)

Diversity of Scolytinae (Coleoptera: Curculionidae) Attracted to Avocado, Lychee, and Essential Oil Lures

The redbay ambrosia beetle, Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae), is an exotic wood-boring insect that vectors laurel wilt, a lethal vascular disease of trees in the Lauraceae, including avocado (Persea americana) and native Persea species (redbay, swampbay). As part of research to identify host-based attractants for X. glabratus, we discovered that a diverse array of non-target ambrosia beetles was attracted to the same substrates as X. glabratus. During Sep–Dec 2009, several field tests were conducted in north Florida (in woodlands with advanced stages of laurel wilt) with traps baited with commercial lures of the essential oils, manuka and phoebe, and with freshly-cut wood bolts of avocado (a known host) and lychee (Litchi chinensis, a non-host high in the sesquiterpene αcopaene, a putative host attractant). In addition, manuka-baited traps were deployed in avocado groves in south Florida to monitor for potential spread of X. glabratus. The combined trapping results indicated that none of these substrates was specific in attraction of X. glabratus. Numerous non-target ambrosia beetles were captured, including 17 species representative of 4 tribes within the subfamily Scolytinae. This report provides photo-documentation and data on the species diversity and relative abundance for a group of poorly-studied beetles, the scolytine community in Florida Persea habitats.

Short-Term Impacts of Laurel Wilt on Redbay (Persea borbonia [L.] Spreng.) in a Mixed Evergreen-Deciduous Forest in Northern Florida

Abstract We examined the immediate effects of laurel wilt on redbay (Persea borbonia [L.] Spreng.) and stand-level characteristics in a mixed evergreen-deciduous forest at Etoniah Creek State Forest in Florida. Percent mortality of redbay in the overstory, sapling, and seedling layers were 100%, 30.2%, and 1.8%, respectively, in the year after the first signs of infection were observed. The diameter distribution of redbay shifted from a reverse “J” pattern to a distribution where the only remaining living stems were &amp;lt;4-in. dbh. Mortality of redbay also resulted in significant reductions in overstory redbay importance values and stand-level density and basal area. Our results suggest that (1) laurel wilt has a more pronounced effect on overstory redbays than smaller stems and (2) redbay mortality caused by laurel wilt can result in modest but significant changes in stand structure.

Potential Effects of Laurel Wilt on the Flora of North America

Abstract Laurel Wilt is caused by a recently identified fungal pathogen infecting plants in the Lauraceae. Laurel Wilt is transmitted by Xyleborus glabratus (Redbay Ambrosia Beetle), which was recently introduced to the southeastern United States from Asia. As the insect expands its range in the US, so too has the disease. A query of the NatureServe Explorer database was used to identify the conservation status of native plant species and recognized plant communities that may be affected by Laurel Wilt. Laurel Wilt affects at least nine plant species, and all fifteen species in the Lauraceae currently found in North America may ultimately prove to be hosts for the disease. Four of the twelve native lauraceous species had been identified as vulnerable to extirpation or extinction, prior to the introduction of Laurel Wilt. There are 55 plant communities in the US and Canada that have a member of the Lauraceae as a dominant or diagnostic species. The majority of these plant communities have been identified a...