Life history and abundance of the predaceous psammophilous mayfly Pseudiron centralis McDunnough (Ephemeroptera: Heptageniidae)

Abstract

Aspects of the life history and abundance of Pseudiron centralis McDunnough were examined in the Sand River in east central Alberta. The population exhibited a univoltine summer life cycle, spending 9 to 10 months of the year in the egg stage. Eggs were large (0.33 × 0.41 mm; mean dry weight, 0.005 mg). Larvae were associated with three types of substrate in the river bed: shifting sand, marginal sand, and gravelly sand. Larvae were active epibenthic predators, feeding primarily on psammophilous chironomid larvae. Larval density was low (< 4 larvae/m2); however, larval mortality also appeared to be low. Stage III and IV larvae exhibited a random dispersion pattern. Annual production (instantaneous growth method) was estimated to be 28.70 and 11.24 mg∙m−2∙year−1 in 1980 and 1981, respectively. The relatively large size of first-instar larvae may allow them to cope with the dynamics of sandy substrates, or may be the minimum size that can effectively capture and consume chironomid larvae. Although chironomid abundance in sandy substrates remains high throughout the year, P. centralis larvae exploit this resource for only a short period.