Influence of photoperiod and temperature on developmental time and number of molts in nymphs of two species of Odonata

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Abstract
Nymphs of the damselflies Enallagma hageni and Enallagma aspersum were collected in North Carolina from August to March and subjected to 11- and 14-h photoperiods at 16 and 21 °C. Development was generally completed more rapidly under long-day conditions. Under all day-length and temperature regimes, developmental time from the middle instars to emergence decreased from a maximum for those nymphs collected in August to a minimum for those collected in March. The two species had similar developmental times under long photoperiods at 21 °C; short photoperiods, however, were more inhibitory to the growth of E. hageni than to E. aspersum. The photoperiodic responses of E. hageni were similar at both temperatures, the developmental times being only slightly slower at 16 °C. In contrast, nymphs of E. aspersum kept at 16 °C showed no photoperiodic response. In both species, diapause or prolonged development occurred primarily in the two instars before the final, but not in the final itself.Extra molts usually accompanied slow developmental times in both species, regardless of photoperiod. The incidence of extra molting was greatest under conditions combining high temperature and short daylength. Extra molts were apparently common in field populations of E. aspersum, but were rare in those of E. hageni.