1. Temperature-induced egg size variation and its effects on successive life stages in the carabid beetle Notiophilus biguttatus were examined.
2. In the laboratory, across temperature regimes, egg size and number were inversely related; number of eggs and total egg mass were higher, but egg size was smaller at high temperatures.
3. Food intake rate was shown not to be involved in the temperature effect on egg size.
4. Within the higher temperature regimes, among females, egg size was negatively correlated with number of eggs and with total egg mass.
5. Data on egg mortality and egg development time did not explain why at low temperature eggs were larger than at high temperature.
6. Larvae hatching from eggs produced at a low temperature were heavier than larvae from eggs produced at a high temperature, irrespective of temperature during development.
7. In a prolonged outdoor experiment (January – July), encompassing the main breeding period of N. biguttatus, egg size decreased and both egg production rate and total egg mass increased in the course of the experiment.
8. In the field, an effect of seasonal change in temperature on adult body size was found; teneral beetles that had their juvenile period early in the season were larger than those that had their juvenile period later in the season.
9. The results of the study suggest a mechanistic explanation in which the egg size response to temperature follows from a difference in temperature sensitivity between two processes in oogenesis; adaptiveness of the temperature response was not clarified.