Diapause and quiescence in eggs of Systellognatha stoneflyspecies (Plecoptera) occuring in alpine areas of Norway

Abstract

Eggs of the stoneflies Diura bicaudata and Arcynopteryx compacta, occurring in the middle-alpine vegetation belt, andDinocras cephalotes not recorded above the sub-alpine, reacted differently to the same temperatures. Those of D. bicaudata and A. compacta had a diapause during the winter. D. cephalotes eggs went into a stage of quiescence when the water temperature was lowered from 16° C to 8° C or below. They remained alive in this stage for about a year, but this quiescence could be broken at anay time when the eggs were transferred to 16 and 20° C.Freezing at -6° C followed by an increase in the water temperature led to a break in the diapause of A. compacta eggs after five months, but not of D. bicaudata eggs.Eggs of D. bicaudata began to hatch after nine months independently of previous freezing followed by an increase inwater temperature. Eggs of D. bicaudata held at a constant temperature of 1.5° C also began to hatch at the same timeas those kept at 8° or 16° C. However, the point of 50 % hatching was much delayed at 1.5° C.The egg diapause of A. compacta and D. bicaudata is an adaptation to areas with a severe climate typified by long cold winters and short summers. The quiescence period of D. cephalotes eggs enables the species to survive outside its normal distribution area.