Photoperiodic Control of the Maintenance and Termination of Larval Diapause in Chironomus tentans

Abstract

DURING recent years, dipterous larvae possessing giant polytene chromosomes have provided important new insight into developmental physiology at the sub-cellular level. This is in large measure attributable to the phenomenon of chromosomal ‘puffing’, which has afforded the opportunity for visualizing the changing pattern of genetic activity within individual tissues during the course of development¹. Clever² has reported significant alterations in the puffing pattern of salivary gland chromosomes from a laboratory population of Chironomus tentans which experienced a state of spontaneously arrested development under conditions seemingly favourable for continued growth and metamorphosis. Although not previously described for this organism, the developmental arrest resembles the diapause which typifies the life-histories of many insect species. Diapause is commonly induced or terminated by extrinsic environmental factors, particularly temperature and photoperiod, which exert their effect by influencing the activity of the endocrine system which regulates insect growth and metamorphosis³. In view of the paucity of information on these matters in the case of C. tentans, coupled with the general utility of dispausing insects and the special cytological attractions of this species for investigations of biochemical mechanisms underlying growth and differentiation, we have examined the natural occurrence of a larval diapause and its photoperiodic control under laboratory conditions.