Embryonic development in Neodiprion sertifer

Progress of embryonic development in Neodiprion sertifer (Geoffroy) was examined in eggs collected in the field during winter and in eggs incubated under controlled conditions in the laboratory. Thirteen embryonic stages can be distinguished with morphological criteria. The development continues throughout winter but requires different temperature thresholds. The first phase proceeds at 5 °C and obviously demands cold because temperatures over 20 °C cause death or malformations. By contrast, in about middle of the development (morphological stage VI) the temperature of 20 °C becomes favourable and supports rapid growth. Hypothesis that the embryos overwinter in a full developmental arrest is rejected on the basis of these results. Term "pseudo-diapause" is suggested for the slow but continuous development.