Abstract: Population density of Sissoo plant infesting eriophyid mite, A. dalbergiae and toxicity of some insecticides on it were studied from April to December 2000. The mite population differed significantly in different months (P<0.001) and different collection cites (P<0.001). Highest population (6.4519±0.19) was observed in the month of May and the lowest (1.8370±0.29) was in August. All test insecticides were toxic to adult mites. The calculated LD50 values of lambda cyhalothrin, malathion, cypermethrin and chlorpyrifos were 0.0541, 0.1760, 0.3249 and 0.6166 μg/cm2 respectively. Lambda cyhalothrin was found to be comparatively more toxic. The order of toxicity was lambda cyhalothrin> malathion > cypermethrin >chlorpyrifos