The experiments were carried out on cotton in the region of Dourados, Mato Grosso do Sul State, in 1996-97. From weekly samples of eggs of Alabama argillacea Hüb. and Heliothis virescens Fab., we determined the level of parasitism, sex ratio and total number of adults of Trichogramma pretiosum Riley emerged from each host egg. The percentage of A. argillacea eggs parasitized by T. pretiosum was null at 31 days after the emergence of the plants (DAE) and increased to more than 60% from the 58th day (DAE)on; sometimes the parasitism reached almost 100%. H. virescens eggs also showed high levels of parasitism by T. pretiosum. The number of adult females emerged from parasitized eggs was always higher than the number of adult males and represented around 60% of the total adults emerged. On the average, around two adult wasps emerged from each egg of A. argillacea or H. virescens. In the region of Dourados, the parasitism by T. pretiosum was high in both A. argillacea and H. virescens eggs, despite the high levels of insecticide use.
Insecta; Gossypium hirsutum; cotton leafworm; tobacco budworm; biological control
