Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

FNZ 6 - Hydraenidae (Insecta: Coleoptera) - Methods and Conventions

Ordish, RG 1984. Hydraenidae (Insecta: Coleoptera). Fauna of New Zealand 6, 64 pages.
( ISSN 0111-5383 (print), ; no. 06. ISBN 0-477-06747-6 (print), ). Published 12 Nov 1984

Methods and Conventions


Mid summer, when stream water levels are low and algal growth is at its greatest, is the most productive time for collecting aquatic hydraenids, although collection data show that they may be taken at any time of the year. For this study often a fine nylon net on a triangular frame was pushed into the gravel immediately downstream from rapids, and the loose gravel was then disturbed above the net, causing beetles and debris to be washed into it. Other collectors have reported good results from examination of the undersides of dead leaves removed from less rapid streams. If large quantities of leaves are involved, they can be left submerged in a container for a few hours, after which specimens can be removed from the surface film of the water.


It is usually convenient to collect these beetles into ethanol (70%), and in the short term at least they can safely be left there. Such specimens yield good genitalia preparations, and most diagnostic features can be seen with a stereoscopic microscope while the specimens are immersed in ethanol. For examination and drawing of the more delicate structures, after maceration in 10 percent potassium hydroxide solution, dissection is best carried out under water because both ethanol and glycerine can collapse some structures. For long-term preservation, dry mounting on cardboard points (Walker & Crosby 1979) is the best method.

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