Mouthpart structure, feeding mechanisms, and natural food sources of adult Bactrocera (diptera: tephritidae)

Abstract

Mouthpart structure, feeding mechanisms, and natural sources of food of the adults of 4 species of fruit flies in the genus Bactrocera-B. tryoni (Froggatt), B. jarvisi (Tryon), B. cacuminata (Hering), and B. cucumis (French)-were studied. When exposed to dry or semisolid food, adult flies always regurgitated fluid from their crop to liquefy and dissolve the food substrate. The regurgitated liquid, along with the dissolved food, was then reingested. Flies without fluid in their crops were unable to liquefy and feed on dry and semisolid food. Liquids were always imbibed without fluids being regurgitated from the crop. Food particles and liquids were ingested only through fine micropores (<0.5 µm) on the pseudotracheae. Particles larger than 0.5 µm were not ingested because the opposing oral lobes were held together tightly during feeding so that the oral opening was never exposed to the food substrate. In addition, interlocking prestomal spines project across the oral opening and also may help prevent the entry of large particulate matter. 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, were thus excluded by the labellar filtering mechanism. This interpretation, together with the results of field observations on their feeding behavior and laboratory and field-feeding experiments (reported elsewhere), suggest that adult fruit flies in the genus Bactrocera use a combination of their fluid-centered 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.