Reproductive Isolating Mechanisms in Fall Armyworm Host Strains (Lepidoptera: Noctuidae)

Abstract

Four potential reproductive isolating mechanisms were studied in two genetically differentiated host strains of the fall armyworm, Spodoptera frugiperda J. E. Smith. The strongest barrier to interstrain mating was temporal partitioning of mating activities throughout the night. The corn strain mated exclusively in the first two-thirds of the night whereas the rice strain mated in the last one-third. Mating preferences assessed by laboratory choice tests also indicated strong assortative mating. Females chose like-strain males 85% of the time. Captures of males responding to caged virgin females in the field provided little evidence of pheromonal differences: ≈40% of the males were attracted to females of the opposite strain. Finally, differences in seasonal abundance were observed. The corn strain achieves highest larval densities in spring and midsummer whereas the rice strain is most abundant in late summer and fall. Adult densities assessed with pheromone traps were consistent with larval densities for the rice strain but not for the corn strain. Very few corn strain males were captured despite high larval densities. These studies support the hypothesis that a combination of characteristics function together to inhibit interbreeding and, thus, provide evidence that supports species status of the two fall armyworm strains.