INDUCTION AND DEINDUCTION IN INSECT PHOTOPERIODISM - EXPERIMENTAL-EVIDENCE AND A MODEL

Experiments with the aphid Megoura viciae Buckton were directed toward quantitative analysis of the cumulative effects of different long- and short-day photoperiods, as dependent on the numbers of light-dark cycles. It has been shown that the accumulation of these effects is a nonlinear process since, as the number of the cycles experienced increases, this process gradually slows down and finally stops. From this observation a suggestion was derived that the kinetics of the cumulative effects depends on interaction of two opposite processes, viz. the increase of the effect due to summation of consecutive daily impulses (induction), and its spontaneous decrease due to degradation (deinduction). The dependence of the kinetics of the cumulative effect on the rates of induction and deinduction was analyzed in the framework of a model proposed earlier. Incorporation of these parameters into the model produced feasible explanations for (a) the compatibility of the quantitative perception of photoperiod with the evident ''all-or-nothing'' overt responses; (b) the dynamics of switches caused by photoperiod reversals, and (c) other aspects of insect photoperiodism. Since temperature coefficients of both parameters may be unequal, the outcome of interaction between induction and deinduction may be different at different temperatures. This provided novel explanations (1) of the well known variations in interaction between the photoperiodic and temperature reactions and (2) of the promotion of development in diapausing insects by chilling.