Age distribution of adult female screwworms (Diptera: Calliphoridae) captured on sentinel animals in the coastal lowlands of Guatemala.

The age structure of screwworm, Cochliomyia hominivorax (Coquerel), populations was studied in the Guatemalan lowlands with the pteridine technique of age determination. Flies (95% were 4-15 d old) were captured on sentinel animals. Mean age was 7.5 d. The oldest fly captured was 21 d old. Most flies visiting wounds were reproductively mature females. Of these, about one-half oviposited once, one-third oviposited twice, and 1 in 10 completed three ovarian cycles (assuming a 3-d interval between clutches). Periodicity in adult capture rates may be related to the reproductive cycle. Results suggest that local populations are composed of a high proportion of synchronized cohorts.