Population dynamics of major insect pests and their natural enemies on cabbage under new alluvial zone of West Bengal.

Population dynamics of major insect pests and their natural enemies on cabbage were studied at Bidhan Chandra Krishi Viswavidyalaya (BCKV), Kalyani, West Bengal(India) during rabi season of 2011-12 and 2012-13. Experiment was laid out in Randomized Block Design with three replications. Cabbage (cv Rareball) seedlings were transplanted in the plot of 9 m area with 45cm x 45cm spacing. Observation was recorded at weekly interval from randomly selected five plants /plot. Peak population of diamond back moth (DBM) was recorded on 1 March and 23 February with13.60 and 14.33 larvae /plant during 2011-12 and 2012-13 respectively. Cabbage aphid reached its peak on 9 February (14.17 aphids/inch leaf) and 16 February (11.03 aphids/inch leaf) of 2011-12 and 201213, respectively. Highest parasitized larvae of diamond back moth by Cotesia plutellae were found on 15 and 8 March with 10.42 and 10.50% larval parasitisation during both the seasons, respectively, whereas maximum coccinellid was observed on 23 February of 2011-12 and 2012-13 crop seasons with 11.67 and 9.67 coccinellids/ 5plants, respectively. Both maximum and minimum temperature had major role to build up the population of diamond back moth, C. plutellae and coccinellids beetle while aphid population was enhanced only by maximum temperature. Relative humidity and rainfall had negative influence on pests and natural enemies during the study period.