Fall Armyworm (Lepidoptera: Noctuidae) Parasitoids: Differential Spring Distribution and Incidence on Corn and Sorghum in the Southern United States and Northeastern Mexico

Nineteen species of parasitoids were recovered from fall armyworm, Spodoptera frugiperda (J. E. Smith), in spring surveys conducted in Florida, Georgia, Alabama, South Carolina, Louisiana, Mississippi, south Texas, and Mexico during 1981–1983. The highest rates of parasitism were in overwintering areas of Mexico–Texas and south Florida, averaging 23.4 and 32.5%, respectively. Chelonus insularis Cresson was the most common species and represented 61.7, 59.6, and 56.1% of the parasitoids recovered from small, medium, and large larvae, respectively. In south Texas and Mexico, C. insularis was recovered from 55.6% of the parasitized small larvae while Archytas marmoratus (Townsend) was the most common species collected from medium (66.7%) and large (47.4%) larvae. A northward progression of C. insularis from overwintering areas during the spring, similar to but lagging behind the progression of fall armyworm populations, was indicated. Hence, C. insularis probably did not overwinter in Georgia or if it did, densities in the spring remained too low for detection by conventional sampling methods. In more northerly areas of the fall armyworm's distribution, C. insularis was of secondary or minor importance; A. marmoratus, Campoletis sonorensis Cameron, Cotesia marginiventris (Cresson), Rogas laphygmae Viereck, and Ophion flavidus Brulle were the most commonly occurring species, particularly in north Florida and in the other states, where rates of parasitization ranged from 9.4% in Alabama to 21.7% in Mississippi–Louisiana. Evidence of differential distribution of some species was indicated by their native scarcity or abundance in defined geographical areas within the temporal limits of the study. For example, Temelucha difficilis Dasch was an important species in south Florida but it was rarely observed in more northerly areas. Conversely, C. sonorensis was absent in collections from south Florida but was an important species elsewhere.