The Pupation Rhythm in Aedes taeniorhynchus (Diptera: Culicidae). II. Ontogenetic Timing, Rate of Development, and Endogenous Diurnal Rhythm of Pupation1
Ontogenetic timing, rate of growth, and endogenous rhythms of pupation and emergence in Aedes taeniorhynchus (Wiedemann) were found to be affected, though unequally, by 5 major environmental factors: nutrition, population density, salinity of the rearing medium, light-dark regime, and temperature. Eggs of this mosquito undergo quiescence after completing embryogenesis (the latter being controlled by temperature and humidity only), and hatch only if conditioned prior to the application of an artificial stimulus. Development through the first 3 instars was affected mainly by temperature, and only slightly by salinities other than the optimum 10% sea water. All 5 factors affected the length of time when fourth instars were present in the cultures. This time was shortened by increased food rations, and lengthened by higher population densities and increased salinity of the medium, but of these, crowding had the least effect at 27°C and LD 12:12. Increased salinity of the medium lengthened the duration of the fourth stadium. All 5 factors also affected the endogenous diurnal rhythm of pupation, which showed a periodicity of 21.5 hours between means of the peaks in 10% sea water, under DD, at either 27° or 32°C, and on basic ration. However, the periodicity could be modified by controlling the time of feeding the larvae. Under LD 12:12, rather than DD, but with the other factors unchanged, the diurnal pupation rhythm had distinct peaks with average periods of 22.3±0.2 hours; higher salinity (more than 25% sea water) delayed the onset of pupation, while excessive numbers of larvae (200) per pan and still higher salinity (50% sea water or more) lengthened the duration of pupation and resulted in 7–8 pupation peaks; the periodicity of the ensuing pupation rhythm was about 23.5 hours. Periods between peaks of pupation became exactly 24 hours under LD 12:12 only when larvae were reared on basic ration, under crowded conditions, and in high salinity. LD regimes affected the endogenous rhythm by producing an advance peak outside the diurnal pattern. Under different 24-hour LD cycles, at 30°, means of pupation peaks were observed between 12h and 18h of the LD cycles. Light-dark cycles had much stronger effects on the pupation rhythm than did temperature cycles. On basic ration, in 10% sea water, and at any temperature between 22° and 34°C, the periodicity of pupation peaks varied from 22.3 to 23.0 hours, thus showing a high degree of temperature compensation. Continuous light delayed the onset of pupation. That the pupation rhythm is a truly endogenous or circadian rhythm was confirmed by entrainment to LD 12:12 and by the high degree of temperature compensation in the periodicity of the pupation peaks. This study also confirmed the hypothesis that the emergence rhythm is dependent on the pupation rhythm, separated by an interval affected by temperature and not by light regime.