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Partnerships between ambrosia beetles and fungi: Varying levels of promiscuity among vectors of the laurel wilt pathogen, Raffaelea lauricola

Randy Ploetz: Tropical Research & Education Center, University of Florida

<div>Culturable fungi were recovered from mycangia of ambrosia beetles associated with trees of <em>Persea humilis</em> (silk bay, one site) and <em>P. americana</em> (avocado, six commercial orchards) affected by laurel wilt, an invasive disease that is caused by a nutritional symbiont, <em>Raffaelea lauricola</em>, of an Asian ambrosia beetle, <em>Xyleborus glabratus</em>. With partial sequences of ribosomal (LSU and SSU) and nuclear (β-tubulin) genes, multiple operational taxonomic units (OTUs) of fungi were identified, most of which could be assigned to previously described species. Nine OTUs were isolated from <em>Xyleborus bispinatus</em>, five from <em>Xyleborus volvulus</em>, five from <em>Xyleborus affinis</em>, three from <em>Xyleborinus saxesenii,</em> two from <em>X. glabratus</em> and two from <em>Xylosandrus crassiusculus</em>. <em>Raffaelea</em> spp. predominated in the <em>Xyleborus</em> species and <em>R. lauricola </em>was present in all except <em>X. saxesenii</em> and <em>X. crassiusculus</em>. <em>Raffaelea arxii</em>, <em>R. subalba</em> and <em>R. subfusca</em> were present in more than a single species of beetle, and <em>R. arxii</em> was the most abundant symbiont in both <em>X. volvulus</em> and <em>X. affinis</em>. <em>Raffaelea aguacate</em>, which had previously been detected only in laurel wilt-affected avocado trees, was detected for the first time in an ambrosia beetle (<em>X. bispinatus</em>). Yeasts (Ascomycota, <span face="AdvTTd3a5f740" style="font-family:AdvTTd3a5f740;" size="1"></span>Saccharomycotina<span face="AdvTTd3a5f740" style="font-family:AdvTTd3a5f740;" size="1"></span>) were common, and distinct populations of these fungi were found in each species of beetle that was examined. We discuss roles yeasts may play in the life cycles of these important pests.</div>