The mustard aphid, Lipaphis erysimi (Kalt.) is the most damaging pest of mustard crop in Bangladesh. Studies were made on the biology of L. erysimi and its control in the laboratory and net house of the Bangladesh Agricultural of Nuclear Institute. The biology of L. erysimi was studies in different varieties of mustard, viz. MM-7, MM-8, MM-19, MM-20, MM- 38/6-98, MM- 2-16-98, Agrani and Strain- 22/12-98 and the management of mustard aphid.

L. erysimi produced the offspring parthenogenetically. Newly hatched nymph developed through four instars in all the eight varieties. The life cycle in the varieties MM-7, MM-20, MM- 38/6-98, Strain- 22/12-98, Agrani, MM-8, MM- 2-16-98 and MM-19 were 12, 11, 11, 10,10, 9, 9 and 9 days respectively. The varieties MM-8, MM- 2-16-98 and MM-19 can be regarded as the most suitable for growth and development of aphids and MM-7 can be regarded as moderately susceptible.

To study the biology with predator performance of C. septempunctata Lineaeus it was found that the incubation period of egg was 2.8 days and the larva consumed 201 aphids in its 8 days larval duration. Total developmental period from egg to adult was 15days. An adult beetle consumed an average of more than 402 aphids.

The present investigation was undertaken to determine the effectiveness of three insecticides (viz-Metasystox-R 25 EC, Dimethion 40 EC and Fentro 50 EC) against mustard aphid (L. erysimi) and their toxic effect to the predator C. septempunctata. The experiments were carried out in the farm and net house of Bangladesh Institute of Nuclear Agriculture (BINA), Mymensingh during the period from November 2001 to February 2002. Findings of the study indicated that Metasystox-R was the most effective against mustard aphid infested plant and aphid population. The use of Fentro 50 EC was found to be more toxic to the larvae and adult of the predator C. septempunctata. The 4^th instars larvae of the predator appeared to be more susceptible to insecticides than adults. Dimethion 40 EC (0.025) proved to be safe insecticide to the predator.

These insecticides also influenced the various growth parameters and yield attributing character leading to much higher seed yield as compared to control. The yields of all the treatments were significantly better than the control. The response of Metasystox R (0.05%) was comparatively better for various growth parameters and yield of mustard.

Study of predation performance of C. septempunctata reflected that the larva consumed 204.33 aphids during 10 days of larval duration. An adult beetle consumed an average 875.01 aphid in 30 days period after emergence. 

           Metasystox R gave maximum cost benefit ratio (CBR) followed by Dimethion and Fentro sprays at comparable doses. The result of the present investigation showed that Metasystix-R was found to be most effective insecticide against mustard aphid while Dimethion was found to be safe insecticides for the predator. Metasystox-R was evaluated as the most economic insecticide for mustard aphid based on cost benefit ratio (CBR).