Assessing fall armyworm (Spodoptera frugiperda)allochronic behavior as a predictor of local strain composition in across United States populations

Authors: MILLER, A - Texas A&M University; TESSNOW, A - Texas A&M University; Meagher Jr, Robert; Nagoshi, Rodney; GULLIGAN, T - Animal And Plant Health Inspection Service (APHIS); SWORD, G - Texas A&M University

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/2024
Publication Date: 10/24/2024
Citation: Miller, A.C., Tessnow, A.E., Meagher Jr, R.L., Nagoshi, R.N., Gulligan, T.M., Sword, G.A. 2024. Assessing fall armyworm (Spodoptera frugiperda)allochronic behavior as a predictor of local strain composition in across United States populations. Frontiers in Plant Science. https://doi.org/10.3389/fpls.2024.1380624.
DOI: https://doi.org/10.3389/fpls.2024.1380624

Interpretive Summary: The fall armyworm is comprised of two genetically distinct host strains that are morphologically identical yet exhibit differences in their behavior and physiology that impact their control. However, the only way to separate corn-strain from rice-strain individuals is through DNA testing, which is time consuming and expensive. Laboratory experiments have shown that the timing of the two strain's mating behavior is different, with corn-strain mating early in the evening (0-5 hours after sunset) and rice-strain mating late in the evening (5-10 hours after sunset). Scientists with the USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology in Gainesville, in collaboration with researchers with Texas A&M University and USDA-APHIS, conducted field experiments in Texas and Florida to test if field populations behaved in a similar way as in the laboratory experiments. The timing of when male moths were collected in pheromone-baited traps was measured, and those moths were genetically identified as either corn-strain or rice-strain. The time of capture was significantly different in both Texas and Florida populations, with corn-strain males captured mostly towards early in the evening and rice-strain captures later in the night. This is the first report of strain-specific time-related behavior across multiple geographically and seasonally distinct populations in the United States. These results assist in the development of time-based models that can be used to predict local strain composition, providing an alternative to expensive and laborious DNA analysis.

Technical Abstract: The fall armyworm, Spodoptera frugiperda (J.E. Smith), is comprised of two genetically distinct host strains that are morphologically identical yet exhibit differences in their behavior and physiology (C = corn strain and R = rice strain). Evidence of ongoing genetic differentiation between the strains necessitates the consideration of strain identity in the research and management of fall armyworm populations, but the logistical and technical burden of genotyping limits strain-specific monitoring efforts. Controlled experiments with laboratory populations have shown that the strains engage in allochronic (“allo”- different, “chronic” – time) mating behavior, with C-strain mating early in the evening (0-5 hours after sunset) and R-strain mating late in the evening (5-10 hours after sunset). Using temporal field collections and genotype data, we show that strain-specific variation in allochronic mating behavior occurs across Texas (TEX) and Florida (FLA) fall armyworm populations, both of which act as primary source populations for annual infestations in the United States. The time of capture was significantly different in both TEX and FLA populations, with C-strain male captures biased towards early in the evening and R-strain captures later in the night. This is the first report of strain-specific allochronic behavior across multiple geographically and seasonally distinct populations in the United States. Allochronic behavior in native populations likely acts as a prezygotic barrier between strains that contributes to reproductive isolation and strain divergence. Furthermore, consistent temporal behavior within the strains facilitates the development of time-based models that can be used to predict local strain composition, providing an alternative to expensive and laborious genotyping tools.