Abstract Laboratory studies were conducted to determine the effect of threshing different sorghum cultivars on Sitotroga cerealella (Oliv.) and Sitophilus oryzae (L.). In a no-choice test, data on progeny production, loss in grain weight, duration of development, and cultivar index of susceptibility indicated that both species of insect responded differently when bred on unthreshed and threshed sorghum grain. On the average, unthreshed sorghum was more suitable than threshed sorghum for the development of S. cerealella, whereas threshed sorghum was found to be more suitable than unthreshed sorghum for S. oryzae development. Threshing did not have any influence on loss in grain weight due to the feeding activities of the larva of S. cerealella, but S. oryzae caused considerably greater loss to threshed than unthreshed sorghum grain. The duration of development of both species of insect was not affected by threshing, but cultivar index of susceptibility was. The different sorghum cultivars had a significant effect on the performance of both S. cerealella and S. oryzae, indicating that some factors in the cultivars and in the insects themselves were responsible for the observed variation. In a free-choice test, where unthreshed and threshed sorghum grain was exposed to S. oryzae in the same chamber, more progeny were produced in the threshed than unthreshed sorghum.