Biological studies of the immature stages of Tabanus taeniola P. de B. in Egypt

Details are given of further studies in Egypt on the biology of Tabanus taeniola P. de B. [cf. last abstract but one]. Egg-masses were collected in the field and taken to the laboratory, where observations were made on the duration of the immature stages at constant temperatures between 7 and 35 deg C and constant relative humidities between 20 and 100% and also at ambient temperatures and relative humidities.The egg-masses contained an average of 259.2 eggs, and the larvae hatched in about 96 h in June and about 213 h in November. Relative humidity had little effect on the duration of the egg stage, but below 50% R.H. none of the eggs hatched. The larvae were found mainly in the mud of the banks of irrigation canals. They were sometimes found among the roots of plants growing on the banks, and relatively large numbers were found inside hollow maize stems that had been thrown into the canals, feeding on snails within the stems. In the laboratory, the larvae were provided with freshly killed larvae of Musca domestica L. as food.The number of larval instars was usually seven but sometimes six, eight or nine. Under insectary conditions, larvae that hatched from eggs laid between May and August completed their development in the same year, the larval stage lasting about 49.7 days, but those hatching from eggs laid after August overwintered in the last instar and pupated in spring after a larval stage averaging 225 days. The development of larvae lasted a mean of 55 days at 32 deg C, 159 days at 27 deg C and 269 days at 22 deg C. The pupal stage averaged about 9.1 days in June-July at ambient temperatures and about 15.2 days in October-November. At constant temperatures, it averaged 33.1 days at 17 deg C and 7.7 days at 35 deg C; pupae kept at 7 deg C did not give rise to adults. The relative humidity had little effect on the duration of the pupal stage, but no adults emerged when it was less than 20-30%.