Nebria brevicollis andPatrobus atrorufus have hibernating larvae and adults that breed in autumn. The young adults hatch in spring and early summer and undergo an aestivation diapause before maturation and reproduction. 2. N. brevicollis hatches earlier and breeds later in the year thanP. atrorufus, so that it shows a summer diapause of about 3.5 months. The aestivation diapause ofP. atrorufus lasts only 1.5 months. 3. In the laboratory the larvae of both species need cold for their development. While cold (+2-4° C) is obligatory forN. brevicollis from the first instar onwards,P. atrorufus larvae tolerate higher temperatures (15° C) except for the third instar. Low temperatures seem to stimulate the development of this species, too, if applied from the first instar onwards. The duration of development ofN. brevicollis is about 1.5 months shorter than that ofP. atrorufus. Metamorphosis again demands higher temperatures at the end of the third instar in both species. 4. The aestivation diapause of the adults is dependent upon the photoperiod. Long-day prevents maturation of the ovaries in the females. Ovarian maturation needs about 1 month short-day inP. atrorufus and 2-3 months inN. brevicollis. In agreement with these resultsP. atrorufus breeds about 1 month andN. brevicollis 2.5 months after summer solstice. 5. Females ofP. atrorufus mature after short-day treatment at 20° C, while those ofN. brevicollis need a decline of temperature in addition. 6. A shift from 20 to 15° C in continuous long-day yields no mature females ofN. brevicollis after 2 months. A small number ofP. atrorufus females (19%) mature after 5 weeks under continuous long-day treatment at 15° C. 7. The males of both species ripen nearly independently of the applied photoperiod.
