Seasonal incidence of some insect pests associated with cabbage (Brassica oleracea var. capitata)

Studies on the seasonal incidence of some insect pests associated with the cabbage were carried out during December 2010 - April 2011. These crops are severely attacked by the different insect pests, mainly cabbage aphid, Brevicoryne brassicae (L.), diamondback moth, Plutella xylostella and their natural enemies. The cabbage aphid, Brevicoryne brassicae (L.) appeared on the second fortnight of January and gradually increased and reached a peak level of 41.82 aphids per leaf during the first fortnight of March. It was found that aphid population increased with increasing maximum and minimum temperature, relative humidity, rainfall and sunshine hours but decreased with increasing wind velocity, whereas predators were very much seasonal and their numerical abundance coincide with the pest. The incidence of diamondback moth, Plutella xylostella commenced from second fortnight of February and gradually increased and reached peak level of 5.96 larvae per plant during the second fortnight of March.