[PLASTICITY OF THE THERMAL REACTION NORMS FOR DEVELOPMENT IN THE EUROPEAN PEACOCK BUTTERLY INACHIS IO (LEPIDOPTERA, NYMPHALIDAE)].

Abstract

The goal of this study was to examine the plasticity of the thermal reaction norms for development in the European Peacock butterfly Inachis io under the effect of different photoperiodic conditions and group versus individual maintenance. The overwintered imagoes were collected in Old Peterhof (near Saint-Petersburg) in May, 2010 and 2012-2013. 12 experimental regimens were used: 4 temperatures (16, 18, 20 and 22 degrees C) and 3 photoperiods (12, 18 and 22 h of light a day). It was found that under short-day conditions (12 h) the caterpillars developed a little faster than under long-day ones (22 h). The developmental temperature thresholds in these two cases did not differ. A linear regression coefficient characterizing thermal sensitivity of development was significantly higher only in males with their development affected by short-day photoperiod stronger than in females. At 18-h day length, the caterpillar development was less temperature-sensitive and characterized by a lower threshold than in shorter and longer days. The influence of short-day photoperiod on the caterpillar development manifested itself most distinctly in the emerging pupae' weight changes: in all the temperature regimens the pupae were lighter at short than at long days. The pupal weight increased as the temperature rose. The found dependence does not agree with the "temperature-size rule". Individual rearing led to a longer duration and lower thermal sensitivity of caterpillar and pupal development as well as to a reduced weight of the pupae. Individual rearing had a stronger impact on the mineral of females than males.