An emergence study of Petalura gigantea (Odonata: Petaluridae)

Abstract

Emergence studies in Odonata provide information on the behaviour, ecology and fundamental demographic parameters in population studies. This paper reports on a study of sex ratio at emergence, pattern and duration of the emergence season, and potential cohort splitting in Petalura gigantea. Sex ratio at emergence varied among years, habitat patches and swamp types. Across all collections, sex ratio varied significantly from a 1:1 ratio, with a bias towards females. The duration of the emergence season varied between sites and years, from at least 45 to at least 70 days, potentially commencing by late October and extending into early January and possibly beyond. Although some evidence suggested cohort splitting, it was not confirmed. Observations of spatially and temporally aggregated emergence clusters are consistent with observed oviposition patterns of individual females, suggesting cohort emergence. Observations of mortalities at emergence and of emergence location are provided; the latter should assist researchers and resource managers in identifying breeding sites in heterogeneous swamp vegetation.

Keywords: Petalura gigantea, Odonata: Petaluridae, emergence, emergence season, emergence pattern, sex ratio, exuviae, cohort splitting

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