The diel oviposition periodicity of wild-caught Anopheles oswaldoi collected from the forest-ecotone habitat in Valencia, Trinidad, was studied in the laboratory by recording the performance of egg-laying individuals and a colony at 2-h intervals. Oviposition was almost exclusively nocturnal, with 95.3% of eggs and 91.3% of oviposition occurrences being observed during the scotophase. During the rest of the day, only 4.7% of eggs (8.7% occurrences) were recorded after dawn (0600-0800 h). Wild-caught females engorged on human blood under laboratory conditions matured, on average, 61.1 +/- 32.3 follicles (range 56-135). Ranges of 50-69, 70-89, 90-109, and > 110 follicles were matured by 12, 4, 4, and 3 gravid females, respectively. These findings provide vector operators with a window of time to maximize the impact of insecticides on An oswaldoi populations.