Presence and prevalence of Raffaelea lauricola, cause of laurel wilt, in different species of ambrosia beetle in Florida USA

Authors: PLOETZ, RANDY - University Of Florida; KONKOL, JOSHUA - University Of Florida; DUNCAN, RITA - University Of Florida; SAUCEDO, RAMON - University Of Florida; CAMPBELL, ALINA - University Of Florida; MANTILLA, JULIO - University Of Florida; Kendra, Paul; CARRILLO, DANIEL - University Of Florida

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/2016
Publication Date: 4/1/2017
Citation: Ploetz, R.C., Konkol, J.L., Duncan, R.E., Saucedo, R.J., Campbell, A., Mantilla, J., Kendra, P.E., Carrillo, D. 2017. Presence and prevalence of Raffaelea lauricola, cause of laurel wilt, in different species of ambrosia beetle in Florida USA. Journal of Economic Entomology. 110(2):347-354.

Interpretive Summary: The redbay ambrosia beetle (RAB) carries a symbiotic fungus that causes laurel wilt, a deadly disease of U.S. trees in the laurel family, including forest species like redbay and swampbay, as well as commercial avocado (valued at $21.6 million in Florida for 2015). A recent study indicated that the lethal fungus could be picked up by other beetles that breed in trees with laurel wilt. Therefore, collaborative research was conducted by the USDA-ARS (Miami, FL) and the University of Florida (Homestead, FL) to determine the extent to which the fungus had spread to other beetles in Florida. A total of 14 species of ambrosia beetle were examined from 9 sites throughout Florida. In addition to RAB, 9 other species tested positive for the fungus. This rapid lateral transfer of a fungal symbiont to other beetle species is unprecedented. It suggests that many beetles may now contribute to the spread of laurel wilt, thus emphasizing the complex epidemiology of this lethal disease. This information will alert other researchers of the need to study additional beetles as vectors of laurel wilt, and to consider these secondary vectors when developing integrated pest management programs to curtail the spread of this disease, particularly in commercial avocado groves in Florida.

Technical Abstract: We summarize information on ambrosia beetle species that have been associated in Florida with Raffaelea lauricola, the primary symbiont of Xyleborus glabratus and cause of laurel wilt, a lethal disease of plants in the Lauraceae. Adult females of 14 species in Ambrosiodmus, Euwallacea, Premnobius, Xyleborus, Xyleborinus and Xylosandrus were either reared from laurel wilt-affected host trees or trapped in laurel wilt-affected stands of the same, and assayed for R. lauricola. In five collections from Persea borbonia, Persea palustris and Persea humilis (native species in the southeastern USA), and four from avocado, Persea americana, extracted mycangia or heads (taxa with mandibular mycangia) or intact bodies (taxa with mycangia in other locations) were surface-disinfested prior to assays on a semi-selective medium for the isolation of Raffaelea (CSMA+). Raffaelea lauricola was identified based on its characteristic phenotype on CSMA+, and the identity of a random subset of isolates was confirmed with taxon-specific microsatellite markers. The pathogen was recovered from 33% (234 of 714) of the individuals that were associated with the native Persea spp., but only 6% (58 of 931) of those that were associated with avocado. Over all studies, R. lauricola was recovered from Ambrosiodmus lecontei, Xyleborinus andrewesi, Xyleborinus gracilis, Xyleborinus saxesenii, Xyleborus affinis, Xyleborus bispinatus, Xyleborus ferrugineus, Xyleborus glabratus, Xyleborus volvulus and Xylosandrus crassiusculus, but was most prevalent in Xyleborus congeners. This is the first record of R. lauricola in Ambrosiodmus lecontei, Xyleborinus andrewesi and Xyleborus bispinatus. The potential impacts of R. lauricola‘s promiscuity are discussed.