Influence of Habitat, Season, and Attractant on Adult Behavior of the Screwworm (Diptera: Calliphoridae) in a Tropical Dry Zone in Costa Rica

Influence of attractant, season, habitat, temperature, and physiological state of the screwworm, Cochliomyia hominivorax (Coquerel), on daily activity and oviposition were examined during a 122 d study in a tropical dry forest in Costa Rica. Flies were marked and released. Numbers of flies visiting baits increased during the wet season and decreased during the dry season; 3 times more flies were observed at baits during the wet season than were observed during the dry season. An average of 33 females and 3 males was observed per day during the study. More flies (3.6 times) were attracted to liver than to sentinel sheep; many flies originally marked at liver failed to return and few of them oviposited on sentinel sheep. Females marked at sheep were recaptured more times and remained in the study area longer. More females marked at sheep sites were recaptured (51.4-54.1%) than those marked at liver sites (32.3-44.7). More than 6 times as many flies were observed at forest than at pasture sites. The physiological state of the female influenced daily activity. High temperatures during midday (>31oC) depressed activity and decreased the number of foraging hours available for flies during the dry season. Decreasing host resources and number of hours available for foraging may be factors that limit screwworm populations in the dry season.