The effect of five constant (10, 15, 20, 25 and 30°C) and the corresponding cycling (25:10, 27.5:12.5, 30:15, 32.5:17.5 and 35:20°C) temperatures at a photoperiod of 16:8 (L:D) h on the development and biometry (HCW, weight) of larva of Sesamia nonagrioides (Lef) Lepidoptera-Noctuidae were investigated. Larvae under both temperature treatments seemed to complete six instars. Final mean head capsule widths did not differ significantly between constant and cycling temperatures. Larval weights increased considerably through larval period under all temperature regimes. However, alternating temperatures were not shown to stimulate larval weight or head capsule widths compared with those of constant temperatures, although tended to result in shorter larval developmental periods. Results are discussed regarding development and seasonal biology of the species.