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Effects of temperature and photoperiod on the duration of larval development in three species of Odonata. Procter, Dennis Lester Coor

Abstract

Corbet has recognised two ecological types of Odonata from temperate regions. He has termed these "spring" and "summer" species, depending upon the presence of a diapause in the final instar. Species possessing a diapause in the final instar are by definition spring species. Corbet believes that spring and summer species represent stages in the colonisation of high latitudes from the tropics. He considers that spring species represent the final stage in adaptation to cold climates, becuase the diapause confers cold resistance on the final instar, and synchronises the short adult life after the relatively long larval period caused by the low temperatures. This study tested several hypotheses arising from Corbet's scheme: (1) Corbet's assumption that spring species develop more slowly (i.e., have lower thermal coefficients for development) at high temperatures than summer species; (2) Corbet's assumption that spring species are more tolerant of low temperature than summer species, and (3) the hypothesis proposed in this study that spring species make the most general use of photoperiod in regulating development. The nymphs of three species of Odonata, Enallagma boreale, Leucorrhinia glacialis and Libellula quadramaculata, were reared under a number of combinations of temperature (10, 15, 20, 25 C) and photoperiod (6, 9, 12, 15, 18 hr). Enallagma boreale, the summer species, developed more rapidly than the two spring species at every temperature. This result supports Corbet's hypothesis that summer species have higher thermal coefficients for growth than do spring species, but does not support his hypothesis that spring species are more tolerant of low temperatures. Photoperiod significantly affected the rate of development in Leucorrhinia glacialis and Libellula quadramaculata at 10 C and 15 C, but Enallagma boreale was not affected by photoperiod at any temperature. This result supports the hypothesis that species from high latitudes (spring species) are more likely to utilise photoperiod in regulating development. Preliminary results suggest that Leucorrhinia glacialis is capable of continuously variable growth rate response to photoperiod. This is the first time that this response has been recorded in an arthropod.

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