The oesophageal diverticulum of Dirioxa pornia studied through micro-CT scan, dissection and SEM studies

Dirioxa pornia (Diptera, Tephritidae) (Island fly) is an Australian native species related to a number of pestiferous fruit flies but, unlike many of the pest species, has not been studied extensively due to its non-pest status. However, due to D. pornia's apparent reliance on the bacteria for survival it is an ideal species to undertake studies into interaction between Tephritid species and bacteria associated with the intestinal tract. The oesophageal diverticulum, which is a blind-ended protrusion of the oesophagus, has been studied, described and characterised in many other Tephritid species. Unlike many other species where the oesophageal diverticulum has been observed the organ was only observed in male D. pornia. It is speculated that this sexual dimorphism the organ may be the primary location to host beneficial bacteria in the involved in the production of the nuptial gift and the mating success of this Tephritid species. In case of D. pornia, however, no study on any area of the digestive system has been conducted. This study was conducted to locate and characterize the oesophageal diverticulum in D. pornia. A virtual dissection of the alimentary tract was made through micro-computer tomography studies. These studies were followed by dissection and scanning microscopy studies to elucidate the presence of bacteria.

The oesophageal diverticulum of D. pornia is part of the foregut and distends from the oesophagus within the head of the fly. The shape of the oesophageal diverticulum corresponds with the Ceratitis type. Scanning microscopy studies of the oesophageal diverticulum show rod-shaped bacterial cells residing along with yeast cells in the lumen. The organ was only observed in male specimens.

This study classifies the oesophageal diverticulum of D. pornia under the "Ceratitis type" of oesophageal diverticula in Tephritid species. The study also proves that micro-CT scanning is possible to locate soft tissues in Tephritid species and the Avizo® Fire software can be successfully used to visualize 3 dimensional (3D) images from x-rays. The methods used in this experiment can be used in future studies for visualising soft tissues of adult Tephritid species through micro tomography. There is sexual dimorphism with the organ only found in males. Finally this study shows that bacteria are present in the oesophageal diverticulum of D. pornia.