none Spodoptera eridania (Cramer) occurred in economic infestations in ca. 50% of the 567 ha of sunflower planted in Alachua County, Florida in the fall of 1982. Outbreaks occurred in sunflower having dense stands of pigweed (Amaranthus sp.), a primary host. After consuming pigweed, the southern armyworm larvae moved en masse to the sunflower. Differences in seed yields from sunflower heads harvested from plants with 0, 50, and 100% defoliation caused by larval feeding were highly significant. Seed yields from plants showing 50 and 100% defoliation were reduced 45 and 98%, respectively, compared to plants showing little or no defoliation. The impact of native parasites on S. eridania populations in sunflower was negligible. Parasites recovered included Opion sp., Chelonus insularis Cresson, Meteorus autographae Muesebeck, and Tachinids. Nutrition; Diet; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Host parasite relationships; Ecology; Population dynamics; Habitat; Man made habitat; Land and freshwater zones; Nearctic region; North America; USA Tachinidae; Chelonus insularis; Meteorus autographae; Ophion (Braconidae ); Lepidopteran hosts; Spodoptera eridania; Prevalence; Spodoptera eridania (Lepidoptera); Florida; Alachua County; Prevalence in lepidopteran host Spodoptera eridania (Noctuidae); Food plants; Helianthus annuus (sunflower), larval feeding damage & economic effects; Dipteran parasites; Tachinidae; Hymenopteran parasites; Chelonus insularis; Meteorus autographae & Ophion; Prevalence; Chelonus; Meteorus; Ophion (Hymenoptera) & Tachinidae (Diptera); Irruption, economic damage to food plant relations; Cultivated land habitat; Irruption & economic damage to food plant; Florida; Alachua County; Irruption dipteran & hymenopteran parasites & damage to food plant