Evolution of Reproductive Isolation of Spodoptera frugiperda

Abstract

Spodoptera frugiperda, the fall armyworm, is a noctuid moth occurring in North and South America. In this species, two host strains have been identified in the late 1980s (Pashley et al. 1985; Pashley 1986), a so-called corn-strain and a so-called rice-strain. The two strains differ in mitochondrial DNA sequences in the cytochrome oxidase I (COI) and NADH dehydrogenase 1(ND1) genes. There are also strain-specific amplified fragment length polymorphisms (AFLP), restriction length fragment polymorphisms (RFLP), a so-called Frugiperda Rice (FR) repetitive nuclear DNA sequence, present in high copy number in the rice-strain and mostly lower copy number in the corn-strain and nucleotide polymorphisms within the triose phosphate isomerase gene (Tpi). Recently, sex pheromone differences have been found between populations of the two strains. However, these differences were not consistent between the studies, suggesting that geographic variation may be confounded with strain-specific variation, or that pheromones may vary within strains as well. The relative importance of the pheromone differences between the two strains still needs to be established, i.e. are males of the two strains differentially attracted to the different pheromone blends. Since other physiological, developmental, and behavioral differences have been found between the strains, in this overview we integrate strain-specific variation in sexual communication with other possible pre- and postmating barriers that are likely involved in the differentiation between the two strains.