Emergence patterns and adult flight season of Anisoptera at a managed wetland site in Hong Kong, southern China

Abstract

Anisoptera emergence in the seasonal tropics was monitored at a 35-ha managed wetland site in Hong Kong from February 2004 to November 2007. Exuviae records of 18 species from multiple emergence screens, exuviae traps and transect surveys were combined. The presence of adults during this period was also monitored. The study site comprised a mosaic of ponds separated by narrow bunds. Exuviae of larvae living amongst dense submerged vegetation, and adults of crepuscular species, were probably under-recorded. Anisoptera emergence was strongly seasonal in all four years, commencing in March, with EM50 – the point at which 50% of the annual population has emerged, expressed as number of days since the start of emergence – falling between April and June, for most species; but emergence also showed considerable inter-year variation, particularly after EM50. Emergence of three species continued into December in at least one year. Extended emergence periods were generally ascribed to multivoltinism associated with unregulated life cycles, presumably facultative in the case of tropical–temperate species. The migrant Pantala flavescens showed no clear seasonality in emergence patterns. Composite species emergence periods over the four years ranged from two to 11 months, with no clear difference between tropical and tropical–temperate species. No species were univoltine. Adult flying seasons usually commenced in March or April, and in eight species continued until at least November, although it is unlikely that any adults survived to the following spring. Five species were on the wing for six months or less. There was considerable phenological variation among species, with life histories commonly intermediate between those of equatorial and higher latitude species.

Keywords: Odonata, dragonflies, Anisoptera, Hong Kong, exuviae, emergence, voltinism, phenology, seasonality

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