PREDATORY POTENTIAL, POPULATION DENSITY AND DEVELOPMENT OF BETASYRPHUS SERARIUS (WEID.), A SYRPHID PREDATOR OF BREVICORYNE BRASSICAE (LINN.) ON CABBAGE.

Field observations on the predatory activity of the syrphid, Betasyrphus serarius (Weid.) on the cabbage aphid, Brevicoryne brassicae (Linn.) were recorded for two years 1993-95 seasons of the cabbage from Novemberto Jully. The study revealed that the density of the predator increased with the density of the aphid and hence showed apositive correlation betweenthem interms of abundance with the peak being in March. The numerical of B. serarius was also correlated with certainabiotic factors such as mean temperature, relative humidity and rainfall. Laboratory studies on larval voracity and duration of development of the predator indicated that a single larve could consume as many as 340 aphids during the larval period of about 13 days. The duration of life cycle of syrphidegg to adult ranged from 24-26 days.