LAUSR

BACKGROUND Field-evolved resistance of fall armyworm (FAW), Spodoptera frugiperda (Smith), has been reported to Bt maize technologies in Brazil. The control failures of FAW by Bt maize increased the use of insecticides for their control. However, no information is available on the interaction between resistant FAW and their response to insecticides. Here, we evaluated the survival of FAW strains on Bt and non-Bt maize in laboratory and field conditions, and their susceptibility to insecticides. RESULTS In the laboratory, resistant FAW larvae reared on Bt and non-Bt maize showed a similar susceptibility to spinetoram (LC50  = 0.16-0.18 µg a.i. cm-2 ) and chlorfenapyr (LC50  = 0.17-0.20 µg a.i. cm-2 ). However, their susceptibility was lower than that of the susceptible strain reared on non-Bt maize: LC50  = 0.05 (spinetoram) and 0.08 (chlorfenapyr) µg a.i. cm-2 . In contrast, heterozygous strains had similar susceptibility to the susceptible strain. In field trials, no differences in FAW survival were detected between strains when the commercial dose of two insecticides was applied in Bt and non-Bt maize. CONCLUSION FAW strains surviving on Bt and non-Bt maize, at the same development stage, have similar susceptibility to insecticides. The integrated pest management practices and insect resistance management importance of these results are discussed. © 2019 Society of Chemical Industry.