Sugar feeding by female tabanids (Diptera: Tabanidae) and its relation to gonotrophic activity

The development stages of terminal ovarian follicles and the parity status was determined in 1311 blood-seeking females of 17 species of Chrysops and 7 species each of Hybomitra and Tabanus in Connecticut in 1978-79. Nulliparous females with follicles in the first 2 stages were observed in 29 species, and nulliparity varied from 28.7% in 181 females of H. lasiophthalma (Macq.) to 90% in 160 females of C. vittatus Wied. Anautogeny prevailed in inland populations. Fructose, sucrose, or both, were detected, by means of an anthrone test, in 71% of 799 nulliparous and 72.3% of 512 parous females, and the prevalence of sugar-positive females varied from 58% in H. sodalis (Will.) to 92% in C. cincticornis Wlk. In an additional 366 tabanids analysed by thin-layer chromatography, 55.9% of 345 positive flies contained glucose, fructose and sucrose, 38.3% contained glucose and fructose, and 5.8% contained glucose alone. Of the 1677 females tested by the 2 methods, 72.8% contained fructose, sucrose, or both. These results indicate extensive feeding on sugars and suggest that these carbohydrates are essential dietary nutrients.