Ultrastructure of the mesonotal mycangium of <i>Xylosandrus mutilatus</i> (Coleoptera: Curculionidae)

Abstract

Mycangial structures of female Xylosandrus mutilatus (Blandford, 1894), an Asian ambrosia beetle recently introduced and now established in the southeastern United States, were examined. In addition to the glandular (secretory) mesonotal mycangium located below the scutellum, nonglandular pit mycangia containing fungal propagules were discovered to occur externally on the scutellum. The ultrastructure of the glandular mesonotal mycangium, which consisted of an outer secretory layer covering an inner paired cuticular sac, is described and illustrated. Both secretory and cuticular layers of the mesonotal mycangium were highly tracheolated. Tracheae and tracheoles in association with a Xyleborine mycangium are reported here for the first time. Type 1 secretory cells were identified and observed passing electron-dense material into the glandular mycangium via efferent cuticular ductules, although type 2 secretory cells were not observed. Secretory cells were not observed in association with the nonglandular pit mycangia.