Sensory Trichites Associated With the Food Canal of Chrysops callidus (Diptera: Tabanidae)

Twelve pairs of putative sensory trichites (= sensilla) in the food canal of Chrysops callidus Osten Sacken are described. Eight paired trichites are located in the distal half of the food canal of all flies in the sample population (n = 26 females), but paired trichites 9 through 12 were found in variable numbers in the proximal half of the canal. Trichites were more closely spaced in the distal half of the food canal, and more widely spaced in the proximal half of the canal, indicating that monitoring blood flow is more critical in the distal region of the canal. Moreover, trichites were not precisely paired, with mean position for each right wall trichite 1 through 8 being slightly anterior to its counterpart in the left wall. A short, funnel-shaped vestibule was evident at the labrum terminus, opening distally to the outside and proximally into the food canal (the vestibule/food canal junction). There were two pairs of sensilla (one pair of basicone design, the other setiform) observed at the base of the vestibule just anterior to the junction of the vestibule with the food canal. These vestibular sensilla were constant in type, number and position, in every member of the sample population.