Population Dynamics of Major Insect Pests and their Natural Enemies in Cabbage

Major insect pests, which caused maximum yield losses in cabbage, were mustard aphid, Lipaphis erysimi, diamond back moth (DBM), Plutella xylostella, Cabbage butterfly, Pieris brassicae, Mustard aphid was noticed from last week of December while diamond back moth was observed during first week of February and the cabbage butterfly appeared during 2^nd week of January during both rabi 2009–2010 and 2010–2011. Peak incidence of mustard aphid (169.9 aphids/plant), diamond back moth (7.9 larvae/plant), cabbage butterfly (27.7 caterpillars/plant) was recorded during 2^nd week of March, 1^st week of March and 2^nd week of March, respectively. Among different abiotic factors, the incidence of mustard aphid, diamond back moth and cabbage butterfly showed significant positive correlation with maximum temperature (r = +0.582,+0.490,+0.572), minimum temperature (r = +0.567, +0.513, +0.570), sunshine hours (r = +0.728, +0.654, +0.726) and evaporation (r = +0.567, +0.372, +0.562), whereas significant negative correlation with morning and evening relative humidity was detected. on the other hand, rainfall was not found to influence aphids, diamond back moth and cabbage butterfly in both years, rainfall (r = + 0.698, +0.779), sunshine hours (r = +0.376, +0.342) and wind (r = +0.291), had significant positive influence on the aphids and DBM larvae while other weather parameters did not have significant influence with aphids and DBM larvae. But maximum temperature (r = + 0.433), minimum temperature (r = +0.352), rainfall (r =+ 0.359), sunshine hours (r = +0.665) and evaporation (r = +0.510) had significant positive influence on the cabbage butterfly caterpillars.