Survival of stream dewatering by Postelichus immsi (Hinton) (Coleoptera Byrrhoidea: Dryopidae)

Abstract

Aquatic byrrhoid beetles are among the most aquatic of beetles. After terrestrial pupation and a brief dispersal flight, the adults enter the water, usually never to leave it again. Aquatic respiration is accomplished using a plastron, or dense network of setae, that retains a bubble. While the plastron functions well for aquatic respiration in flowing water, it does not function well in still water and, for some unknown reason adults that are removed from water often die quickly. Even when shortly returned to water, they commonly die within an hour (unpublished data; White 1978). As currently known, the genus Postelichus is composed of six described and one undescribed species. Its range extends from the southwestern United States of America through Mexico. It is typically a desert inhabitant and can be the dominant macroinvertebrate in desert streams, often with remarkably high numbers. As with many others who study aquatic byrrhoids I have assumed that all species needed permanent water, and likewise that finding them in a stream is an indicator of the stream’s permanence. However, some cases have argued against the need for constant water (Brown 1987). While working in Arizona in July 2007, with Doug Post, another aquatic beetle specialist, I discovered another such case. The location was: Arizona: Yavapai Co.; Bloody Basin; Tangle Creek (34u08.7669 N, 111u47.7759 W). When we first drove to Tangle Creek it was dried up as far as we could see except for one pool in the shade of a tree. Finding aquatic byrrhoids absent in the