Micro-computed tomography permits enhanced visualization of mycangia across development and between sexes in Euwallacea ambrosia beetles

Symbiosis can facilitate the development of specialized organs in the host body to maintain relationships with beneficial microorganisms. To understand the developmental and genetic mechanisms by which such organs develop, it is critical to first investigate the morphology and developmental timing of these structures during the onset of host development. We utilized micro-computed tomography (μCT) to describe the morphology and development of mycangia, a specialized organ, in the Asian ambrosia beetle species Euwallacea validus which maintains a mutualistic relationship with the Ascomycete fungus, Fusarium oligoseptatum. We scanned animals in larval, pupal and adult life stages and identified that mycangia develop during the late pupal stage. Here we reconcile preliminary evidence and provide additional morphological data for a second paired set of structures, including the superior, medial mycangia and an inferior, lateral pair of pouch-like structures, in both late-stage pupae and adult female beetles. Furthermore, we report the possible development of rudimentary, or partially developed pairs of medial mycangia in adult male beetles which has never been reported for any male Xyleborini. Our results illustrate the validity of μCT in observing soft tissues and the complex nature of mycangia morphology and development.