Susceptibility ofPerseaspp. and Other Lauraceae to Attack by Redbay Ambrosia Beetle,Xyleborus glabratus(Coleoptera: Curculionidae: Scolytinae)

Abstract

Redbay ambrosia beetle (RAB), Xyleborus gla bratus Eichhoff (Coleoptera: Curculionidae: Sco lytinae), a native of Asia, was first discovered in the USA near Savannah, Georgia in 2002 (Haack 2001; Rabaglia et al. 2006). RAB is an effective vector of Raffaelea lauricola T.C. Harr., Fraedrich & Aghayeva (Harrington et al. 2008) that causes laurel wilt (LW), a lethal disease of several trees in the Lauraceae in the southeastern USA (Crane et al. 2008; Mayfield et al. 2008). Ambrosia beetle adults bore through the bark and into the xy lem (wood) where they lay eggs, then adults and larvae cultivate and feed on symbiotic ambrosia fungi that grow in the galleries. Native Persea (Laurales: Lauraceae) species appear to be pre ferred hosts. LW is responsible for high mortality of redbay [P borbonia (L.) Spreng.], swampbay [P palustris (Raf.) Sarg.], and sassafras [Sassa fras albidum (Nuttall) Nees] in Alabama, Flor ida, Georgia, Mississippi, North Carolina and South Carolina (Fraedrich et al. 2008; Hanula et al. 2008; Gramling 2010). As LW encroaches upon the Lake Wales Ridge ecosystem in south central Florida, silkbay (P. humilis Nash) is also showing susceptibility to LW and is dying. Addi tional species affected by LW include avocado (P. americana Mill.), spicebush [Lindera benzoin (L.) Blume], and other woody Lauraceae (Fraedrich et al. 2008) (Table 1). The susceptibility of 5 avocado cultivars of Mexican, Guatemalan or West Indian origin to RAB and LW was demonstrated by Mayfield et al. (2008). However, with more than 23 West In dian cultivars grown in Florida, it is necessary to determine their susceptibility. Moreover, as an adventive species to the North American conti nent, RAB might affect other valuable New World species. Most Persea species are of Mexican, Cen tral American, or South American origin. These Persea may have significant value in germplasm collections, some have been discovered recently, and some have resistance to diseases that afflict their commercial relative, the avocado (Skutch et l. 1992; Scora & Bergh 1992; Zentmyer & Schieber 1992). Thus, their susceptibility to RAB and LW warrants evaluation. Another member of the Lauraceae of much concern is the California bay laurel [Umbellularia californica (Hook. & Arn.) Nutt.], a dominant hardwood species of the U.S. Pacific Coast. Through inoculation experi ments, Fraedrich (2008) demonstrated that U. californica is susceptible to LW. With continued westward spread of LW, the host status of U. cali fornica needs to be confirmed. The 3 studies presented here evaluate sus ceptibility to RAB and LW in: 1) 13 West Indian avocado cultivars; 2) 10 non-commercial Persea spp., 1 Beilschmidia sp. (a genus related to Per sea), and 3) U. californica. First, no-choice ex periments were conducted to determine if RAB would bore into avocado cultivars not screened previously by Mayfield et al. (2008) and follow ing similar methodology. Avocado cultivars 'Ber necker', 'Beta', 'Brooks late', 'Choquette', 'Don nie', 'Dupuis', 'Hall', 'Loretta', 'Lula', 'Monroe', 'Simmonds', 'Tower 2' and 'Waldin' (4 plants each) were planted in 10-gallon pots in a screenhouse at he Plant Sciences Research and Education Unit, University of Florida (UF), Citra, Florida in VI 2008. Two plants of each cultivar were infested by enclosing 4 newly emerged 9 RAB (UF colony reared) within a mesh sleeve on the lower trunk. Two plants per cultivar were uninfested controls. Entrance holes and perseitol (white exudate from wounds) were monitored for 4 wk. Severity of wilt symptoms was scored using the following LW in dex: 0 = no wilt; 1 = wilt, no leaf necrosis; 2 = wilt, 10% necrosis or defoliation; 3 = wilt, 30% necrosis/ defoliation; 4 = 50% necrosis/defoliation; 5 = 75% necrosis/defoliation; 6 = 100% necrosis/defoliation