Interspecific abundance and seasonal incidence of aphids and aphidophagous predators associated with cabbage.
Among the three species of aphids that damaged the cabbage crop, Myzus persicae (Sulz.) constituted 45.30% of the total population, followed by Brevicoryne brassicae (L.) (33.88%) and Lipaphis erysimi (Kalt.) (20.82%). M. persicae was prevalent throughout the cropping season, but was most active during December and January (159.83-239.90 nymphs and adults/3 leaves). L. erysimi was active during the early part of the cropping season with peak activity during November and first fortnight of December (118.82-136.09 nymphs and adults/3 leaves). B. brassicae was a late starter which commenced its activity from mid-December and lingered on the crop till harvest during March end. Its peak incidence was noticed during January and February (119.69-263.18 nymphs and adults/3 leaves). Out of the four species of coccinellid predators, Coccinella transversalis F. was the dominant species constituting 55.08% of the total population followed by Cheilomenes sexmaculata (Fab.) (27.73%), Micraspis discolor (Fab.) (12.05%) and Coccinella septempunctata L. (5.14%). C. transversalis and C. sexmaculata appeared during mid-November and attained their peak population during January and February (7.27-10.94 and 4.26-5.08 grubs and adults/10 plants, respectively). M. discolor and C. septempunctata appeared during mid-December and mid-January, respectively. They reached the peak population during February (2.44-3.34 and 1.29-1.83 grubs and adults/10 plants). Of the two species of syrphid predators, Ischiodon scutellaris (Fab.) was overwhelmingly more numerous (80.06%) than Eumerfus albifrons Walker (19.94%). While I. scutellaris appeared during early November, E. albifrons appeared during early December. The peak activity of I. scutellaris was observed during January and first fortnight of February (8.64-11.45 larvae/10 plants), whereas that of E. albifrons during the second fortnight of January and first fortnight of February (2.79-4.06 larvae/10 plants).