INTERSPECIFIC AND INTRASPECIFIC VARIATION OF THE DURATION AND THERMAL REQUIREMENTS FOR EGG DEVELOPMENT IN CARABID BEETLES (COLEOPTERA. CARABIDAE) IN THE NORTH-WEST OF RUSSIA

The adult carabid beetles Amara communis, A. nitida, Carabus granulatus, Platynus assimilis, Poecilus versicolor, Pterostichus oblongopunctatus (spring breeding species), P. melanarius (sic) P. niger (autumn breeding species) were collected near Arkhangelsk, St. Petersburg, Moscow and Bryansk in May-June. Females and males were kept in pairs at 20 degrees C and 22 h light per day. The eggs laid by females were maintained at constant temperatures (12, 14, 16, 18, 20 and 22 +/- 0.1 degrees C). The development time for each egg was measured within 0.5 day From the values of the individual development rate (a reciprocal of development time), at all temperatures the thermal constants for development - the coefficient of the linear regression (CLR) of the development rates on temperature, the sum of degree-days, and the thermal threshold for development (TT D) were calculated. The egg development time was found to differ significantly between the species, except for A. communis, A. nitida, and C. granulatus. The values of CLR (i.e. the slopes of the regression lines) and TTD varied rather distinctly between the species and populations that revealed the differences in the thermal requirements for egg development. In the spring breeding species the mean egg development time was significantly shorter, and the CLR and TTD values were, on the average, higher compared to those in the autumn breeding species. Intraspecific latitudinal variation of the development time and the thermal requirements for egg development were revealed. The eggs laid by beetles from the Arkhangelsk population developed faster than the eggs of the same species from the southern populations at all experimental temperatures. These differences were not great but statistically significant. At the same time, the differences between the northern and southern populations of the same species in the CLR and TTD values appeared insignificant in most cases. The authors concluded that the main eco-physiological adaptation of carabid beetles during their spread to the north was the shortening of development time under the whole favorable temperature range, while the CLR and TTD values little varied.