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THE LIFE‐HISTORIES OF TWO SUMMER SPECIES OF DRAGONFLY (ODONATA: COENAGRIIDAE)
Author(s) -
CORBET PHILIP S.
Publication year - 1957
Publication title -
proceedings of the zoological society of london
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.915
H-Index - 96
eISSN - 1469-7998
pISSN - 0370-2774
DOI - 10.1111/j.1096-3642.1957.tb00334.x
Subject(s) - voltinism , instar , odonata , biology , larva , facultative , metamorphosis , ecology , diapause , ecdysis , spring (device) , zoology , dragonfly , mechanical engineering , engineering
SUMMARY1 The life‐histories of two dragonflies, Coenagrion mercuriale (Charp.) and Ceriagrion tenellum (Villers) have been determined by taking regular larval samples from populations in Hampshire and Glamorganshire. 2 Both species are semivoltine. Eggs are usually laid in June and July and hatch about a month later. Larvae spend the first winter at a length of about 4–5 mm. Most individuals pass the second winter in the penultimate instar, which they enter in autumn. Ecdysis to the final instar occurs abruptly in spring, and is followed closely by metamorphosis and emergence. 3 A facultative diapause may exist in the penultimate instar, but a synchronizing factor operates between resumption of growth in spring and emergence. A mechanism is suggested whereby synchronization of emergence could be achieved by a rising series of lower temperature thresholds for successive developmental stages in spring. Some ecological implications of this mechanism are discussed. It is concluded that their high thermal coefficient for larval growth would deny univoltine species the economic use of such a system, and that there are ecological grounds for a sub‐division of summer species on this basis.