Non-destructive observation of the mycangia of Euwallacea interjectus (Blandford) (Coleoptera: Curculionidae: Scolytinae) using X-ray computed tomography

X-ray microtomography has been applied successfully to obtain reliable microstructural information of many insect species. Nonetheless, the technique has not been widely applied to ambrosia beetles. The ambrosia beetle Euwallacea interjectus (Blandford) was first recorded as a vector of plant pathogenic fungus Ceratocystis ficicola Kajitani & Masuya, which has caused serious wilt disease in many fig orchards in Japan since 1999. Previous studies of E. interjectus have not described the mycangia (fungus-storing organ) in detail. In this study, we non-destructively examined the internal structure of an adult female of E. interjectus through computed microtomography scans. Paired mycangia were observed on typical computed tomography cross-sections of the head. Each mycangium, ovoid in shape, was located in tissues just posterior to emarginated notch of eyes, adjacent to pharynx. Three dimensions (length × width × depth) of the mycangia were measured on stereography. We confirmed the absence of mycangia in the other body parts, such as elytra, prothorax and coxa of legs.