(1st Place) Patterns of field-based allochronic behavior of Spodoptera frugiperda host strains in Texas and Florida provide evidence of alternative reproductive isolation mechanism between strains

The fall armyworm (FAW), Spodoptera frugiperda, is a polyphagous noctuid moth comprised of two genetically and behaviorally distinct strains known as the C- and R-strains. Although host plant use has been proposed to play a role in strain divergence, there is little evidence in support of larval host use as a mechanism that promotes reproductive isolation among mobile adults that do not mate in association with specific plants. In contrast, laboratory studies and recent field evidence support the hypothesis that strain-specific differences in overnight mating activity periods provide a mechanism that promotes their reproductive isolation. These studies indicate allochronic (i.e., “different time”) differences in which the C-strain mates early in the night whilst R-stain mates later. The goals of this study were (1) to examine the pattern and prevalence of strain-specific allochronic mating-related activity across multiple sites and years, and (2) to determine the accuracy of nighttime activity as a predictor of strain identity. We used time-stamped collections in conjunction with novel genotyping techniques to assess the time at which C- and R- strain moths or their hybrids were collected in pheromone-baited traps over three years across multiple sites in Texas and Florida. Our results support allochronic divergence as a key reproductive isolation mechanism involved in maintain genetic differentiation between the two between FAW strains. The use of collection time as a predictor of strain identity may provide a simple way to estimate the strain composition of local FAW populations in support of strain-specific IPM strategies.