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.
Ambrosia beetles have emerged as significant pests of avocado ((Persea americana Mill. [Laurales: Lauraceae])) due to their association with pathogenic fungal symbionts, most notably Raffaelea lauricola T.C. Harr., Fraedrich & Aghayeva (Ophiostomatales: Ophiostomataceae), the causal agent of the laurel wilt (LW) disease. We evaluated the interaction of ambrosia beetles with host avocado trees by documenting their flight height and daily flight periodicity in Florida orchards with LW. Flight height was assessed passively in three avocado orchards by using ladder-like arrays of unbaited sticky traps arranged at three levels (low: 0-2 m; middle: 2-4 m; high: 4-6 m). In total, 1,306 individuals of 12 Scolytinae species were intercepted, but six accounted for ~95% of the captures: Xyleborus volvulus (Fabricius) (Coleoptera: Curculionidae), Xyleborinus saxesenii Ratzeburg (Coleoptera: Curculionidae), Euplatypus parallelus (Fabricius) (Coleoptera: Curculionidae), Xyleborus bispinatus Eichhoff (Coleoptera: Curculionidae), Xyleborus affinis Eichhoff (Coleoptera: Curculionidae), and Hypothenemus sp. (Coleoptera: Curculionidae). The primary vector of R. lauricola, Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae), was not detected. Females of X. volvulus showed a preference for flight at low levels and X. bispinatus for the low and middle levels; however, captures of all other species were comparable at all heights. At a fourth orchard, a baiting method was used to document flight periodicity. Females of X. saxesenii and Hypothenemus sp. were observed in flight 2-2.5 h prior to sunset; X. bispinatus, X. volvulus, and X. affinis initiated flight at ~1 h before sunset and Xylosandrus crassiusculus (Motschulsky) (Coleoptera: Curculionidae) at 30 min prior to sunset. Results suggest that ambrosia beetles in South Florida fly near sunset (when light intensity and wind speed decrease) at much greater heights than previously assumed and have species-specific patterns in host-seeking flight.
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