Mouthpart structure and feeding in adult fruit flies - Bactrocera sp. and Ceratitis capitata (Wiedemann) (Diptera: Tephritidae)

Abstract

Adult Bactrocera and Ceratitis capitata (Diptera: Tephritidae) possess specific structural modifications on the labellum that provide a labellar flitering mechanism which determines the types of food that they ingest in nature. The inner surface of the labellum has a series of fine tubes or pseudotracheae that radiate from the oral opening to the labellar margin. The pseudotracheae have fine micropores (<0.5µm) that open into the lumen of the pseudotracheae. Interlocking prestomal spines project across the oral opening. During feeding, adult flies press the open labellum against the feeding surface and regurgitate fluid from their crop to liquefy and dissolve the food substrate. The regurgitated fluid along with the dissolved food is then reingested. Flies without fluid in their crops are unable to liquefy and feed on dry and semisolid food. Dilute liquids are always imbibed without fluids being regurgitated from the crop. Liquids and dissolved food particles smaller than (<0.5µm) are ingested through the micropores into the lumen of the pseudotracheae, while the interlocking prestomal spines prevent entry of large particulate matter via the oral opening. Adult fruit flies thus use a combination of their fluid-centred mode of feeding and their labellar filtering mechanism to feed on fruit juices, leachates and bacteria (Enterobacteriaceae), which constitute their primary source of food in nature. Particles larger than bacteria, such as yeasts, fungal spores, and pollen grains that are commonly found on fruit and leaf surfaces where adult flies commonly forage, are thus excluded by the labellar filtering mechanism.