Environmental controls in the seasonal succession and synchronization of development in some pond species of damselflies (Odonata: Zygoptera)
Sawchyn, W. W.
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Environmental factors which control seasonal succession and synchronization of development in seven species of pond-dwelling Zygoptera were investigate. A three phase succession was observed. Three species of Coenagrionidae, Coenagrion angulatum, C. resolutum and Enallagma boreale which overwintered as nymphs, emerged simultaneously and synchronously commencing during the last week of May. They were followed by Lestes disjunctus disjunctus, L. unguiculatus and L. dryas in late June and early July, then by L. congener near mid July. Synchronization of development in the coenagrionid species is produced by a temperature and photoperiod influenced diapause in the penultimate and final instars, by differences in thermal growth coefficients in different instars during spring development, and by a threshold temperature for emergence higher than that for nymphal development. Members of the second group overwinter as eggs in late stages of embryonic development, and are prevented from hatching in the fall by a diapause who development is accelerated first by low temperature then by long photoperiod. Absence of suitable temperatures in the winter prevent post-diapause development. Further synchronization is obtained through simultaneous wetting which initiates development in the spring. Finally, L. congener overwinters in the pre-blastokinesis stage of embryonic development. Dioapause development is accelerated by low temperature; however, no effect of photoperiod was observed. Winter conditions prevent hatching when diapause is terminated. Hatching is synchronized by diapause, by simultaneous wetting of the eggs and by differential embryonic development and hatching temperatures in the spring. Rapid nymphal development in the latter two groups sustains the developmental synchrony which was established at the time of hatching. Seasonal succession was discussed in relation to the factors which control hatching and nymphal development in the three species types.