William Lambert, University of Georgia, Bugwood.org
Many states use pheromone traps, unfortunately the pheromone lure has a high rate of non-target captures. During a study in 1999 the most significant non-target capture was Leucania phragmatidicola, a moth that does not even have a common name. Blacklight traps are not immune from problems with misidentification. It is important to be able to distinguish between these species. The fall armyworm is a significant pest of sweetcorn while L. phragmatidicola feeds on grasses. If non-target captures are misidentified as fall armyworm, it causes trap counts to inflate resulting in unnecessary treatments.
Hopefully we will have a new lure within the next few years that will lower the incidence of non-target capture. Both the fall armyworm and L. phragmatidicola are medium sized brown moths that can appear at first glance to be of the same species. Complicating matters is that specimens collected from traps are frequently worn and tattered, with many of the wing and body scales missing. However, there are a few easily identified characteristics that can be used to distinguish between these species. This guide lists four characters, in the order from easiest to most difficult.
Specimens are most easily examined with a small hand lens available at many agricultural and nature stores. To use this key compare the characters of moths from your trap with the pictures of the fall armyworm. For comparison we have also included pictures of L. phagmatidicola, a moth that is frequently captured using the fall armyworm lure. With some diligence and experience it becomes easy to tell them apart. The fall army worm was first characterized by J. E. Smith in 1797 and is recognized taxonomically as being in the order Lepidoptera, the family Noctuidae, the genus Spodoptera, and the species Spodoptera frugiperda (species names include both the genus and the species). Voucher specimens for both species have been archived at the Frost Entomological Museum, identification number 2000-2.
Diagnostic feature #1
Lateral Spots near the distal margin of the forewing, and texture of the wing.
The forewing of the fall armyworm has a modeled appearance (Figures 1 and 3) and the rear wing has a purple sheen in direct light. The forewing of L. phragmatidicola has a number of spots running parellel to the distal margin. Additionally the forewing of L. phragmatidicola has a rough texture with wing veination clearly visible.
Diagnostic feature #2
Color of the scales adjacent to the claspers.
The male fall armyworm has white colored scales on either side of the claspers at the end of the abdomen, even though the outer scales are tan. In contrast L. phragmatidicola has only one color of scale (tan) surrounding the claspers. This character is usually intact even on damaged specmens.
Diagnostic feature #3
Banding pattern behind the eyes
The fall armyworm has a single broad dark band immediately posterior to its eyes. The dark band is clearly visible from both an anterior (Figure 6) and dorsal (Figure 8) view. L. phragmatidicola has three thin dark bands behind the eyes (Figures 7 and 9). When specimens are damaged or worn this character may be obscured. You many need to view the enlarged image to see this character clearly.
Diagnostic feature #4
Shape of the claspers
This character is only useful for male specimens which is quite functional when using pheromone traps because they only capture male moths. The scales from the posterior end of the moth must be removed before this character can be fully observed. Scales are best removed with a soft hair brush as the claspers are very delicate and easily damaged. The claspers of the fall armyworm have a round shape, very similar to a bellows or paddle (Figure 10 and 12). The claspers of L. phragmatidicola come to a sharp point at the dorso-posterior end (top, rear) and have a shape invagination about two thirds from the bottom (Figure 11 and 13).
Taxonomic References for the fall armyworm (S. frugiperda)
Todd, E. L., and R. W. Poole. 1980. Keys and illustrations for the armyworm moths of the noctuid genus Spodoptera guenee from the western hemisphere. Annals of the Entomological Society of America 73:722-738
Smith, J. E., 1797. in Abbot, J., and J. E. Smith. The natural history of the rarer lepidopterous insects of Georgia, 1, 2, xv 214 pp. 104 plates.
Taxonomic References for the L. phagmatidicola
Covell, C. J. JR., 1984. Peterson field guides: Eastern Moths. Houghton Mifflin Company. Boston Forbes, W. T. M., 1952. Lepidoptera of New York and neighboring states, Noctuidae Part III. Cornel University Agricultural Expiment Station. New York State College of Agriculture.
Pheromone References for the fall armyworm (S. frugiperda)
Tumlinson, J. H., E. R. Mitchell. P. E. A. Teal. R. R. Heath. and L. J. Mengelkoch. 1986. Sex Pheromone of fall armyworm, Spodoptera frugiperda (J. E. Smith) identification of components critical to attraction in the field. Journal of Chemical Ecology. 12: 1909-1926 Mitchell, E. R., J. H. Tumlinson. and J. N. Mcneil. 1985. Field evaluation of commercial pheromone formulations and traps using a more effective sex pheromone blend for the fall armyworm (Lepidoptera: Noctuidae). Journal of Economic Entomology. 78:1364-1369 Jones, R. L., A. N. Sparks. 1978. (z)-9-tetradecen-1-ol acetate a secondary sex pheromone of the fall armyworm, Spodoptera frugiperda (J. E. Smith). Journal of Chemical Ecology. 5: 721-725 Sekul, A. A., and A. N. Sparks. 1967. Sex pheromone of the fall armyworm moth: isolation, identification, and synthesis. Journal of Economic Entomolgy. 60:1270-1275
Pheromone References for the L. phagmatidicola
Roelofs., 1971 Chemical Releasers in Insects, A.S. Tahori, ed., Gordon & Breach, London 1975
This page created by Chris Harding and Shelby Fleischer with support from the Pennsylvania Vegetable Growers Association and the USDA NE-IPM program. We also want to thank John Grehan from the Frost Entomological Museum, John Rawlins from the Carnegie Museum of Natural History for their assistance and independent identification and Dick Bean, Maryland Department of Agriculture. All images are the property of Chris Harding and are not to be used without his consent.
Last updated March 2000