Cold‐hardiness and development of eggs of Rhopalosiphum insertum

Abstract. 1. The eggs of Rhopalosiphum insertum (Walker) showed a seasonal increase in cold‐hardiness under field conditions. Their supercooling point fell from ‐35°C in November to below ‐40°C in January, then rose to‐35°C or above by March. 2. Laboratory experiments demonstrated that both temperature and date affected cold‐hardiness of the eggs. The supercooling points of eggs kept at 16 h photoperiod or in darkness did not, however, differ significantly. 3. Eggs brought from the field into warm, long‐day conditions would not hatch until after mid‐January. After this date, per cent hatch was significantly greater in 16 h photoperiod than in darkness; it did not differ between eggs kept at 5 or 0°C, but was reduced at ‐5°C. 4. It is concluded that eggs of Rinserturn are in diapause until mid‐January, and that hatching rate and cold‐hardiness are determined by separate environmental factors.