Comparison of olfactory and gustatory genes between Spodoptera frugiperda and Spodoptera litura.
Recently, a gluttonous pest, the fall armyworm Spodoptera frugiperda invaded in China, ravaging crops and threatening the vast supply of maize. Compared with its relative, the tobacco cutworm Spodoptera litura, S. frugiperda mainly prefers graminaceous plants such as corn, rice and wheat. In addition, there are differences in the reproduction characteristics of the two pests; such as mating and spawning frequency. Differences in olfactory and taste related genes between the two relatives are possibly one important cause. In this study, we collected and identified olfactory and gustatory genes of the two relatives, constructed phylogenetic trees of these genes, test the selection signals and analyzed the divergent amino acid site in some odorant binding proteins. We totally identified 261 olfactory genes in S. frugiperda, which are obviously more than those in S. litura (179); we identified 233 gustatory genes in S. frugiperda, slightly more than those in S. litura (217). Among the olfactory genes, the number of the olfactory binding protein (OBP) genes were most remarkably different between the two relatives. Phylogenetic analysis showed that there was a Noctuidae specific clade of the OBPs, in which the number of genes in S. frugiperda was much higher than that in S. litura. OBPs in another group belonging to antennal binding protein I (ABPI clade) also showed increased gene numbers in S. frugiperda. Two gene copies in this clade showed positive selection signal in S. frugiperda. Furthermore, S. frugiperda specific replacements in two amino acids were predicted to affect the protein function. This study provides not only clues for the understanding of the genetic mechanism underlying feeding and mating characteristics of S. frugiperda and but also reference and genetics material for its biological control.