An experiment was carried out to evaluate the effect of the insecticide Applaud (buprofezin 25% WP) on the silkworm Bombyx mori (L.). This insecticide belongs to the class of insect growth regulators (IGR). The larvae were fed on leaves treated with 3 different concentrations (0.5, 1, 2 g/liter) of Applaud on the 1st d of each instar. Analysis of data with the Tukey–Kramer test at 1% significant level revealed that mortality and larval duration did not differ among the treatments. On the contrary, the larval weight, which was estimated just before mounting (procedure during which the mature larva climbing on a branch or other material to spin the cocoon), differed among the treatments. Also, cocoon weight, shell weight, and cocoon sericin and fibroin content were different among the treatments, except the shell cocoon ratio. Maximum weight was observed in the controls and minimum in the last instar treatments. Our data suggest that supplementation of Applaud through food to larvae does not affect their mortality rate. On the contrary, it affects larval growth and cocoon parameters.