Title: Insect photoperiodism: Seasonal development on a revolving planet
Abstract: quiescence, and since insects that fail to become dormant may not survive, these traits provide enormous selective advantage.In quiescence, insects respond directly to adverse environmental factors such as low temperature (i.e.cold torpor) or dehydration and are rapidly reactivated upon removal of these factors (Henneguy, 1904).In diapause, however, insects respond to 'token' stimuli, not in themselves adverse (Lees, 1955), such as the seasonal changes in photoperiod described above; these factors act well in advance of winter and provide time for the accumulation of the metabolites (lipids and proteins) needed during the dormant phase.Sometimes diapause is associated with an acquired cold tolerance (Horwath & Duman, 1982, 1983; Lee & Denlinger, 1991) and since it also occurs at a species-specifi c stage of development (e.g. in egg, larva, pupa or adult) may engender mutual synchrony within the population that facilitates mating success after reactivation in the spring.Quiescence and diapause often involve similar 'downstream' reactivation pathways, either the brain (PTTH)prothoracic gland (ecdysteroid) axis in the regulation of larval and pupal (i.e.developmental) dormancies, or the brain-corpus allatum (juvenile hormone) axis in adult (i.e.reproductive) dormancies (Denlinger, 1985).They differ, however, in their 'upstream' control: diapause is regulated by a brain-centred photoperiodic clock measuring day-or nightlength and considered by many authors to be based Insect photoperiodism: Seasonal development on a revolving planet *