CHAPTER 6 - THE PHOTOPERIODIC RESPONSE

Abstract

This chapter discusses the photoperiodic response curves. Most experimental work on the induction of insect diapause has been carried out using stationary photoperiods. Groups of insects are usually exposed to a series of day-lengths and to constant dark (DD) or constant light (LL) throughout their development or sensitive period and the proportion of the population entering diapause plotted as a function of day-length. The curves obtained are called photoperiodic response curves. The photoperiodic response curve is a product of natural selection and differs in populations from different latitudes and geographical areas. At higher latitudes, the longer the summer days, the greater rate of change in day-length and the shorter summer season are reflected in a longer critical day-length than in areas further south. More northerly populations frequently achieve fewer generations per year than those in the south. Altitude and the proximity to the warming influence of oceans also affect the photoperiodic response and voltinism. The important characters of the photoperiodic response are genetically controlled and, therefore, inherited in all cases by a polygenic system.