Baseline susceptibility of Spodoptera frugiperda (Lepidoptera: Noctuidae) to Cry1F Bacillus thuringiensis toxin

The fall armyworm, Spodoptera frugiperda, is a tropical polyphagous insect pest that can affect multiple cropping systems. Currently fall armyworm infestation is managed with insecticides and corn hybrids expressing insecticidal proteins derived from Bacillus thuringiensis. Field resistance to Cry1F Bt toxins was reported among fall armyworm populations from Puerto Rico in 2007. The early detection of insect resistance is important to making appropriate management decisions in a timely manner and to inform IRM decisions. The objective of the current study is to establish baseline susceptibility of U.S. fall armyworm populations to the Cry1F Bt insecticidal protein, emphasizing collections from geographic locations where fall armyworm overwinters in the U.S. Fall armyworm neonates were exposed to artificial diet treated with increasing Cry1F concentrations, and both mortality and growth inhibition were evaluated after 7 days. The range of variation in Cry1F susceptibility indicated by growth inhibition was similar to that indicated by mortality. Inter-population variation in susceptibility varied between 5 and 8 fold in two years of studies.