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Like other ambrosia beetles, Xyleborus volvulus Fabricius (Coleoptera: Curculionidae) lives in a mutualistic symbiotic relationship with fungi that serve as food source. Until recently, X. volvulus was not considered a pest, and none of its symbionts were considered plant pathogens. However, recent reports of an association between X. volvulus and Raffaelea lauricola T.C. Harr., Fraedrich & Aghayeva (Ophiostomatales: Ophiostomataceae), the cause of the laurel wilt disease of avocado (Persea americana Mill. [Laurales: Lauraceae]), and its potential role as vector of the pathogen merit further investigation. The objective of this study was to evaluate three artificial media containing sawdust obtained from avocado or silkbay (Persea humilis Nash) for laboratory rearing of X. volvulus. The effect of R. lauricola in the media on the beetle's reproduction was also evaluated. Of the three media, the one with the lowest content of sawdust and intermediate water content provided the best conditions for rearing X. volvulus. Reproduction on this medium was not affected by the sawdust species or the presence of R. lauricola. On the other two media, there was a significant interaction between sawdust species and R. lauricola. The presence of R. lauricola generally had a negative effect on brood production. There was limited colonization of the mycangia of X. volvulus by R. lauricola on media inoculated with the pathogen. From galleries formed within the best medium, there was 50% recovery of R. lauricola, but recovery was much less from the other two media. Here, we report the best artificial substrate currently known for X. volvulus. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The redbay ambrosia beetle, Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae), is an exotic wood-boring pest that vectors Raffaelea lauricola T.C. Harr., Fraedrich & Aghayeva (Ophiostomatales: Ophiostomataceae), the etiologic agent of laurel wilt. To date, all confirmed U.S. hosts of X. glabratus and suscepts of laurel wilt are members of the family Lauraceae. However, in previous research, an unknown variety of lychee, Litchi chinensis Sonn. (Sapindales: Sapindaceae), was found to be highly attractive to X. glabratus and elicited boring behaviors. Therefore, a study was undertaken to evaluate two commercial cultivars of lychee, 'Brewster' and 'Mauritius', for susceptibility to attack by X. glabratus, for transmission of R. lauricola, and for development of laurel wilt disease. In no-choice laboratory bioassays, 35 and 44% of females bored into cut bolts of 'Mauritius' and 'Brewster', respectively. Similar boring was observed on the trunks of two live 'Brewster' trees; but after 3 mo, there was no evidence of beetle reproduction, no symptoms of laurel wilt, and no recovery of R. lauricola from tissue associated with beetle galleries. Lychee trees artificially inoculated with an isolate of R. lauricola (RL4) that kills lauraceous hosts of this pathogen were asymptomatic after 1 mo, and assays for R. lauricola were negative. Chemical analysis indicated that lychee emits several sesquiterpene constituents in common with the Lauraceae, but at lower levels. Based on these data, we conclude that L. chinensis, although attractive to female X. glabratus, is not a likely reproductive host. This may be due to the inability of lychee wood to support growth of R. lauricola, the presumed primary nutritional symbiont of X. glabratus. [ABSTRACT FROM AUTHOR]

Avocado, Persea americana, is an important fruit crop in the tropics and warm subtropics. Laurel wilt, caused by Raffaelea lauricola, is a systemic vascular wilt of avocado that spread recently to Florida, an important producing state in the USA. As fruit and seed of avocado produced in Florida are sold in other states and countries where this crop is produced, there is concern that commerce in these commodities might spread this disease. Potted, fruit-bearing trees were artificially inoculated with R. lauricola, and plants were systemically colonized by the fungus. In no instance did infection progress further than the hilum (87 total fruit), as determined by re-isolation of R. lauricola on a semi-selective medium or its detection, with qPCR and high fidelity PCR, of diagnostic small subunit (SSU) 18s rDNA. Thus, it would apparently be safe to propagate avocado with seed from trees affected by this disease. Pedicels/peduncles and hila associated with these fruit were colonized by the pathogen. The latter tissues would be associated with/attached to marketed fruit, but they do not harbour the pathogen's ambrosia beetle vector, Xyleborus glabratus. Thus, commerce in avocado fruit appears to be a negligible risk for expanding the geographic range of laurel wilt. [ABSTRACT FROM AUTHOR]

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 α-copaene, α -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. [ABSTRACT FROM AUTHOR]