A preliminary guide to the identification of dragonfly larvae (Odonata) from the Alligator Rivers regin of the Northern Territory

"March 1993".

Project Number: Odonate Taxonomy Key - YH/6/14.

MDFRC item.

Dragonflies are a prominent component of the invertebrate fauna o f the aquatic environments of the Alligator Rivers Region. The adult dragonfly fauna is well known following surveys conducted by CSIRO as part of the Environmental Fact-Finding Study in 1972-73, and later surveys by J.F. Hutchinson (1978) and J.A.L Watson (1979). Seventy eight species were recorded from the Alligator Rivers Region (ARR) (Watson and Abbey 1980) and an additional 19 species have been recorded from outside the region, making a total of 97 species occurring in the “Top End” of the Northern Territory (Watson pers. comm. 1991). They are thought to be the third most speciose aquatic macroinvertebrate order in the region. However, the larvae of the majority of species remained undescribed and unidentifiable. As with most aquatic insect orders, the taxonomy of Odonata is based on the characteristics of the adult stage. The larvae of many species, well known as adults, are unknown, not having been reared to associate the different life stages. Effective biological monitoring of aquatic habitats in the ARR requires that both larval and adult stages can be identified to the level of species. However the lack of associations and the absence of a key to immature stages has made identification difficult beyond the level of genus. The present study aimed to obtain associations of immature larvae and adults by rearing larvae to the adult stage for all species in the ARR. During the project 43 species, including 12 previously associated larvae, were reared at the OSS Laboratory. A total of 66 species were associated, the larvae of 35 species were previously unknown, whilst the remaining 31 species were known from previous associations. This guide provides an identification key to all known odonate larvae in the ARR. It provides additional comments on the characteristics of the mature larvae, notes on ecological information for each species and lists locality data for each species. Explanatory figures and a glossary have been included to explain specialised odonate terminology used in the key.