Neotropical Entomology 34(6):937-944 (2005) Interaction between Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), Campoletis flavicincta (Ashmead) (Hymenoptera: Ichneumonidae) and Bacillus thuringiensis aizawai, in Laboratory ABSTRACT -Larvae of healthy Spodoptera frugiperda (J.E. Smith), parasitized by Campoletis flavicincta (Ashmead), infected by Bacillus thuringiensis aizawai, and both parasitized and infected, were obtained in the laboratory and fed with corn leaves. Parasitized and infected larvae showed less leaf consumption (in average 2.3 cm 2 ) than the others, but did not differ from only parasitized larvae. Mean mortality of larvae both parasitized and infected was higher (96.5%) than the only parasitized (78.4%) and only infected ones (44.3%). The feeding period of the infected larvae (in average 29.6 days) did not differ from that of the healthy ones, in spite of having a longer larval period. Offsprings from pairs of parasitoids that had emerged from infected larvae did not have the biological characteristics modified. Therefore, the combined use of the parasitoid and the bacterium results in higher mortality and less foliar consumption and does not result in damage to the parasitoid.KEY WORDS: Fall armyworm, biologic control, microbial control, natural enemy RESUMO -Lagartas de Spodoptera frugiperda (J.E. Smith) sadias, parasitadas por Campoletis flavicincta (Ashmead), infectadas por Bacillus thuringiensis aizawai e parasitadas e infectadas foram obtidas em laboratório e alimentadas com folhas de milho. Lagartas parasitadas e infectadas apresentaram menor consumo foliar (em média, 2,3 cm 2