none Immature forms of Cotesia diurnii Rao & Nikam, a larval parasitoid of Exelastis atomosa (Wals) were studied under laboratory conditions (24 +- 1 degree C, 55-60% R.H.). The newly deposited eggs were white, thin walled and typically hymenopteriform. The eggs averaged 0.166 mm in length and 0.042 mm in width. The first two instars were vesiculate type and third hymenopteriform. The length and width of the 3 instars averaged 0.90, 0.150 and 2.5, 0.37 and 3.2, 0.48 mm respectively. The mean length and width of the mandibles in 3 instars averaged 0.035, 0.014 and 0.061, 0.020 and 0.08, 0.035 mm respectively. Pupae averaged 3.2 mm. in length and 1.00 mm in width. There exists a significant correlation between larval age and larval body form (L : P lt 0.01; W : P lt 0.05).