The aphid endoparasitoid Diaeretiella rapae (McIntosh), parasitizing green peach aphid Myzus persicae (Sulzer), mustard aphid Lipaphis erysimi (Kaltenbach) and cabbage aphid Brevicoryne brassicae (L.) in Kangra, Kullu, Mandi, Shimla, Hamirpur, Sirmaur, Una and Bilaspur districts of north Indian Himalayan state, Himachal Pradesh was studied. At different locations, parasitism by D. rapae in December, January, February and March ranged from 0.00 to 5.30, 0.00 to 16.40, 19.30 to 31.20 and 0.00 to 49.80%. Under field conditions, experiments were conducted to evaluate the side effect of some commonly used chemical insecticides and biopesticides on D. rapae. Percent parasitism by D. rapae in dimethoate treated plots was negatively affected, and it reduced from 11.85 to 0.01%, whereas biopesticides didn't affect the parasitism. Further laboratory investigations assessed the suitability of aphids viz. M. persicae, B. brassicae and L. erysimi as hosts for mass rearing of D. rapae. Among the aphid hosts, second nymphal instar of M. persicae was found to be the larger in size, followed by B. brassicae and L. erysimi. D. rapae reared on M. persicae were larger in size compared to those reared on B. brassicae and L. erysimi. Further, M. persicae reared on Capsicum annuum proved to be the best aphid host for D. rapae based on high percent parasitism (58.60%) and high fertility (76 eggs/female). The current research advises that D. rapae can be mass reared on aphid hosts in a laboratory that would supplement augmentative biological control in rapeseed-mustard. Our results also demonstrate that biopesticides can be used against aphids infesting rapeseed-mustard, with limited risk to the parasitoid, D. rapae and can be a fruitful option to chemical-based insecticides.