Larval black fly feeding (Diptera: Simuliidae): use of endogenous glycoconjugates

Abstract

Histochemical techniques were used to determine the origin and possible function of glycoconjugates in the head region of larval black flies. Late-instar larvae of Simulium vittatum Zetterstedt and Gymnopais dichopticoides Wood were stained with Alcian blue at pH 0.5, 2.5, and 3.2, aldehyde fuchsin, and periodic acid – Schiff's reagent to determine the chemical affinities of the glycoconjugates. Additionally, larvae were fed inert Dayglo®particles and then sectioned and stained as above to determine the origin of glycoconjugates observed in the gut contents and on the labral fan rays. Examination showed that carboxylated and weakly sulphated glycoconjugates are secreted from what are redescribed here as dorsal and ventral cephalic glands. These glands are associated with the labral, mandibular, hypostomal, and maxillary epidermis. The secretion product is not used to enhance food capture or handling. Instead, it is hypothesized that these glycoconjugates aid in formation of mouthpart structures during the pharate stages, or facilitate ecdysis. Glycoconjugates, previously observed in the gut and on the surface of the mouthparts, must be of exogenous origin.