Abstract: Efficacy of Dimlor 662 EC was monitored against corn leaf aphid, Rhopalosiphum maidis (Fitch) under three different micro-climatic conditions i.e. seedling of maize sown on plastic pots covered with glass chimneys, seedling in test tubes, and maize leaves placed on petri dishes. Maize leaves and seedling were painted with serial dilutions i.e. 0.0003, 0.0006, 0.0012, 0.0025, 0.0050 and 0.01 percent. It was found effective and statistically non significant in all micro-climatic conditions. A liner regression model was developed between concentration and percentage mortality. The LC90 were calculated as 0.0024, 0.0041 and 0.005 percent, respectively. This study will help in determining appropriate dosage of insecticide for the aphid control would be beneficial in resistance monitoring, IPM development, and product screening.