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 (> 31 degrees C) 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.

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. Pradel model mark -release -recapture estimates of survivorship, , recruitment, f , and the rate of density-independent population growth, , are presented for eight mark -recapture studies of the screwworm Cochliomyia hominivorax (Coquerel) (Diptera: Calliphoridae) from Costa Rica, totalling 19 573 released and 4476 recaptured flies. Corroborative estimates of survivorship and the rate of population growth based on an extensive review of the literature are also reported. Weighted-mean ± standard error of the mean (SEM) mark -release -recapture estimates of survivorship, recruitment and the rate of population growth were = 0.798 ± 0.008, f = 0.193 ± 0.008 and = 1.005 ± 0.002, respectively. Population doubling time was estimated from at 139 days. Estimates of and from the literature both exceeded those calculated by mark -recapture methods and estimates of population doubling times were consequently shorter.

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