Figure 1

Activity records of representative males of the haH and laH strains of D. helvetica monitored at the breeding site of each strain in the field in natural light-dark 14.1:9.9 h cycles under NFT and CT regimes. Black portions of each time bar indicate the scotophase and the open portion indicates the photophase. SR and SS denote the sunrise and sunset, respectively, while M, N and E denote the morning, noon and evening, respectively. Onset of activity of both males of the haH strain occurred in the forenoon ~4.5 h after SR in both temperature regimes, but the end of activity of male # 211 (A) occurred ~1 h before SS in NFT regime, and that of the male # 36 (C) occurred ~1 h after SS in CT regime. Onset and end of activity in both males of the laH strain occurred ~1 h before SR and ~0.4 h after SS under both temperature regimes, but the Ψ _M-E of the male # 51 (E) in NFT regime was 4.8 h, while that of the male # 24 (G) was 2.2 h in CT regime. The mean entrainment activity profile of 21 males of each strain for 11 days is shown in histogram format (B, D, F, H). Males of the haH strain had a unimodal activity pattern in both temperature regimes; however, activity ended ~1 h before SS in the NFT regime (B) and ~1 h after SS in the CT regime (D). Males of the laH strain had bimodal activity patterns in both temperature regimes; however, Ψ _M-E was 5.2 h in NFT regime (F) and 2.3 h in the CT regime (H).