Predation by Coccinella septempunctata L. on the Cabbage Aphid, Lipaphis erysimi (Kalt.) in India

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Abstract
The growth of population from 2 Lipaphis in the absence of predator indicated that the numbers rose to a peak on 20 Jan. and then fell. Decline was not due to the influence of temperature. Probably plants had become unfit to provide food for further increase. Growth of population from 5 Lipaphis on cabbage leaves harboring various densities of earlier infestation revealed that the rate of increase on the reinfested plants was lower as compared with that on plants which had not been infested before; the decline after the peak was faster among the reinfested and that the earlier reinoculation carried out the higher was the peak of populations both on the preinfested and the controls. Studies on the growth of population from 2 Lipaphis in the presence of a predator beetle proved that the earlier the predator was introduced the less the prey population increased. The efficiency of Coccinella in finding Lipaphis was studied by offering 4, 8, 16, 32, 64, 128 aphids/plant. Each beetle found and consumed half the prey individuals which were distributed evenly; the data did not disagree with this hypothesis (x[image]1.165, P=0.95). The beetle normally eats 62 aphids per day. In the fields, Coccinella does not begin to multiply until after the increase of Lipaphis has been limited presumably by the deterioration of the food plants. This deterioration may be attributed to changed weather conditions (density independent) and by intraspecific competition.

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