Influence of plant defense signaling and innate insect metabolic differences to the overall performance of fall armyworm (Spodoptera frugiperda) corn and rice strains on maize as a host

Abstract

The fall armyworm (FAW,Spodoptera frugiperda) is a well-known crop pest that feeds mainly on grasses. Separate strains are known to infest maize (corn) and rice that show varying degrees of developmental and metabolic differences, as well as reproductive isolation. Here we show that the greater performance of the corn compared to the rice strain on maize leaves may be explained by several factors. Maize plants respond to herbivory by the rice strain with greater levels of defense hormone signaling and greater accumulation of defensive benzoxazinoids. Moreover, measurements of the activity of a glucosyltransferase involved in benzoxazinoid metabolism and the transcript levels of the encoding gene revealed that the corn strain had higher benzoxazinoid detoxification potential than the rice strain. The two strains also exhibit constitutive differences in the expression of an alternate variant, with potential consequences for differential regulation of the glucosylation activity. These factors may account for the better performance of corn strain larvae on maize leaves, perhaps in combination with the other differences we found in maize defense metabolites after FAW herbivory by untargeted metabolomics.