Figure 2.
Curves passing through mean values (N = 22) of the natural light intensity (open circles) and environmental temperature (filled circles) obtained at the breeding site of the haH strain (A) at Hemkund-Sahib (4,121 m) and at the breeding site of the laH strain of D. helvetica (B) at Birahi (1,132 m). Data were collected from 1 to 21 July 2005 when the natural photoperiod was ~14 h. Note that light intensity curves were almost similar at both breeding sites but the temperature curves were strikingly dissimilar. Ψoand Ψe (vertical lines) denote the phase of activity onset and the phase of activity offset, respectively. The haH flies began activity ~4.5 h after sunrise (SR) when the temperature and light intensity were ~19°C and 79,000 lux, respectively, while the laH flies began activity ~1 h before sunrise when the temperature and light intensity were ~20°C and 1 lux, respectively. The haH flies terminated activity 1.4 h before sunset (SS) when temperature and light intensity were ~14°C and 17,000 lux, respectively, while the laH flies terminated activity ~0.4 h after sunset when the temperature and light intensity were ~22°C and 30 lux, respectively.