Evaluation of Screen Barriers on Redbay Trees to Protect Them From <I>Xyleborus glabratus</I> (Coleoptera: Curculionidae: Scolytinae) and Distribution of Initial Attacks in Relation to Stem Moisture Content, Diameter, and Height

Abstract

Fine mesh screen was used to create a physical barrier to prevent redbay ambrosia beetles, Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae), from accessing various parts of the boles of redbay trees, Persea borbonia (L.) Sprengel, and infecting them with the laurel wilt fungus, Raffaelea lauricola (T.C. Harrington, Fraedrich, & Aghayeva). Screen barriers prevented beetles from attacking boles of mature redbay trees from the ground to 1 or to 3 m and from 1 to 3 m above ground. Untreated control trees were sampled more extensively to determine how location of initial attacks varied with height, diameter, and moisture content of the wood. Screening did not affect tree survival, and all of the trees died within 243 d from the beginning of observation. Initial points of attack by X. glabratus varied from ground level to heights of at least 6.6 m. Trees showed characteristic laurel wilt symptoms with as few as two X. glabratus entry points. The number of attacks exhibited nonlinear relationships with diameter (P = 0.0004; r2 = 0.82) and height (P = 0.0013; r2 = 0.69) but were not correlated with moisture content. Attacks increased gradually with increasing stem diameter up to approximately 10 cm after which the attacks became more numerous. X. glabratus attacks were most numerous on the tree bole near the ground. Attacks then declined as tree height reached 2-3 m. From 3 to 8 m, attacks were relatively consistent.