Effects of Notonecta glauca predation on Cyphon larvae (Coleoptera: Scirtidae) populations in small, seasonal ponds

Aquatic Cyphon (Coleoptera: Scirtidae) larvae are characteristic inhabitants of small, seasonal ponds across a wetland at Aberlady Bay, Scotland, UK, but not found in adjacent, large permanent ponds. This distribution may be an example of the use of spatial refugia to escape abundant invertebrate predators found in large ponds. Notonecta glauca is a regular component of the permanent waters but erratic colonist of the small seasonal ponds. The surface dwelling habit, activity and lack of intrinsic defences of Cyphon larvae make them very vulnerable to N. glauca. N. glauca was added to seven of the small, seasonal ponds and numbers of Cyphon larvae in these treatment ponds were monitored and compared to those in six control ponds. By the end of the experiment Cyphon numbers in treatment ponds were reduced by more than 50% compared to controls, despite differences in pond hydrology, position, vegetation and other fauna present across replicates, suggesting that predation is an ecologically important process affecting the distribution of Cyphon larvae.