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 crop 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 has been reported in Puerto Rico, in 2007. The early detection of insect resistance is important to making appropriate management decisions in a timely manner according to an IRM program. The objective of the current study is to establish a U.S. fall armyworm baseline susceptibility 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 B. thuringiensis concentrations, and mortality and growth inhibition were evaluated after 7 days. The range of variation in B. thuringiensis susceptibility indicated by growth inhibition was very similar to that indicated by mortality. Interpopulation variation in susceptibility was less than 2 fold suggesting that the observed susceptibility differences reflect natural variation in B. thuringiensis susceptibility among fall armyworm populations rather than variation caused by prior exposure to selection pressures.