Thermal reaction norms for development and their photoperiodic modification in the Bryansk population of the european peacock butterfly <em>Inachis io</em> (Lepidoptera, Nymphalidae)

Abstract

The thermal reaction norms for development (TRN, i.e. the regression coefficient or thermal sensitivity coefficient, the lower developmental threshold and the sum of degree-days) were investigated at 4 temperatures (16, 18, 20 and 22 °C) and 3 photoperiods (18, 16 and 12 hours of light per day) in the Bryansk population of European Peacock butterfly Inachis io. Photoperiodic modification of TRN for caterpillars was found: while the length of the day decreased there was a gradual increase of a lower threshold (10.7, 11.3 and 12.4 °C at 18, 16 and 12 h, respectively) and the slope of the regression line of development rate on temperature to abscissa axis became steeper. This means that there is an increase of the thermal sensitivity of development. Under short-day conditions pupae were lighter than under long days in all temperature regimes. The pupal weight increased with increasing temperature under long- and under short-day conditions. The development of caterpillars is characterized by a lower thermal sensitivity than the development of pupae.