Biology and seasonal incidence of aphid, Brevicoryne brassicae on Cabbage

Observations showed that a single female gave birth to 85.8±1.08 nymphs on an average within its life span. Nymphs developed through four instars and transformed into adults with an average of 8.3±0.83 days. Adult females (wingless) were dull green to grey coloured and covered with a whitish waxy powder. The average pre-natal, natal and post natal periods were recorded as 3.2±0.63, 16.1±4.09 and 10.7±1.16 days, respectively. The average female adult longevity was recorded as 25.6±4.60 days. The incidence of this aphid varied from 20 to 410/3 leaves/plant. The incidence was highest during 12^th SW. These insects showed significantly negative correlation with maximum relative humidity while non-significant positive correlation was observed with maximum and minimum temperature.