The findings reported in this work reveal that Dryopteris filix-mas aqueous and ethanolic extracts, its powder and pyrethrum extract caused depressive effect on the developmental stages of this pest and a significantly dose dependent alterations in the haemolymph and fat body biochemistry of the larva of rice-moth, C. cephalonica- a major pest of stored cereal commodities. Their order of toxicity is Pyrethrum extract > D. filix-mas aqueous extract > D. filix-mas ethanolic extract > D. filix-mas powder. These biopesticides disrupt the metabolic balance of the larva resulting into reduced total protein level, decreased DNA, RNA levels, RNA/DNA ratio, activity of alkaline phosphatase and glycogen content and enhanced amino acid level, reducing sugar level and acid phosphatase activity. These biochemical perturbations in the metabolic frame work may impair the physiological fitness of the larva and thereby contribute to the lethal action of the biopesticide. D. filix-mas is comparatively less effective than pyrethrum extract but since pyrethrum extract is much costly, so, D. filix-mas may be preferred for the effective control of C. cephalonica and other lepidopterous pests.