Submitted to: Environmental Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/6/2004
Publication Date: 8/1/2004
Citation: Nagoshi, R.N., Meagher Jr, R.L. 2004. Seasonal distribution of fall armyworm (Lepidoptera: Noctuidae) host strains in agricultural and turf grass habitats. Environmental Entomology. 33(4):881-889. Interpretive Summary: Spodoptera frugiperda (J. E. Smith), or fall armyworm (FAW), is periodically a significant pest of maize, sorghum, forage grasses for livestock, turf grasses, rice, cotton and peanuts whose range extends from southern Canada to most of South America. It is a migratory pest that cannot survive freezing winters, hence the infestation of most of North America stems from populations overwintering in south Florida and parts of Texas. Controlling FAW in these relatively localized overwintering areas prior to migration could significantly reduce FAW damage in more northern states. However, complicating our understanding of FAW field behavior is the existence of two morphologically identical strains that display significant differences in resistance to certain pesticides, susceptibility to different plant cultivars, and host plant preference. Because of difficulties in identifying strains, little is known about their behavior in the field and their distribution in different habitats. In this study scientists at the Center for Medical, Agricultural, and Veterinary Entomology, used molecular biology techniques combined with pheromone trapping to examine strain-specific population behavior in agricultural and grass habitats in south Florida. Substantial variations in the seasonal distribution of the two strains were found suggesting previously unknown differences in migration behavior and response to environmental factors. The data and techniques developed here make possible future studies to examine specific questions in strain behavior and population dynamics. This information is essential for the development of area-wide control strategies that could interfere with or delay the northward migration of FAW and therefore mitigate the damage from this pest in most of the continental United States and Canada.
Technical Abstract: Male fall armyworm moths [Spodoptera frugiperda (J. E. Smith)] were captured in pheromone traps over a 16-month period in selected sites in southern Florida. Molecular markers were used to determine whether individuals were of one of two host strains (historically designated 'rice-strain' and 'corn-strain'). Traps placed in agricultural areas showed a population peak in the spring (Mar-May) and fall (Oct-Dec) with a prolonged decline in numbers in summer (Jul-Oct) and a smaller reduction in mid-winter (Jan). The host strain distribution during these periods varied significantly, suggesting strain-specific seasonal population patterns. Both strains were captured in substantial numbers during the spring peak, but surprisingly only the rice-strain showed an increase in capture rates during the fall despite the presence of sweet corn (Z. mays) throughout this period. Trap captures in a sod (turf grass) farm were comprised almost entirely of the rice-strain and showed a bimodal seasonal distribution similar to that seen in the agricultural areas, with peaks in the spring and fall. These results represent the first indication that the two host strains might have substantially different population dynamics and suggests the possibility that the rice-strain is the predominant fall armyworm pest during the fall and winter growing periods in Florida agricultural sites. It further indicates that the two strains can display a markedly different response to seasonal environmental cues. The implications of these findings on our understanding of fall armyworm migration are discussed.