The life history of a temperate zone dragonfly living at the edge of its range with comments on the colonization of high latitudes by Neotropical genera of Zygoptera (Odonata) alt-text


Of the many Zygopteran genera that occur in the Neotropics, only five (Hetaerina, Archilestes, Lestes, Argia, and Ischnura) are represented north of 40°N in North America, and only three of these (Hetaerina, Archilestes, and Argia) probably had a tropical origin. In the two genera of Lestidae (Archilestes and Lestes) the life history of temperate-zone populations is usually regulated by an egg diapause, whereas in the two genera of Coenagrionidae (Argia and Ischnura) larval diapause synchronizes life histories with seasonal temperature changes. This paper presents data on the life history of a northern population of a species in the first genus, Hetaerina americana living in a geothermally influenced stream near to the northern edge of the species’ range in western North America. Larval growth is affected by temperature and differs between warmer and cooler years, but generally larvae appear to grow very rapidly during summer and even grow over winter. Two peaks of larval recruitment each year and a decrease in final stadium size over the summer may be evidence for bi-voltinism, and the absence of final stadium larvae in October, November, and December indicates a short-day regulatory diapause in F-1 larvae. A long-day diapause which prevents autumnal metamorphosis of larvae appears not to be present. It is not known whether the tactics that allow New World species of Zygoptera to survive at mid- to high-temperate latitudes are also present in their tropical congeneric relatives, but it does appear that diapause expression has been associated with speciation in the temperate zone.

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