Original paper

Emergence of Leuctra nigra (Plecoptera) from a southern English stream

Petersen, Irene; Hildrew, Alan G.

Abstract

The emergence of the stonefly Leuctra nigra into pyramidal traps was related to the supply of emergent substratum locally available in a small, stony stream. Hence, in a manipulative experiment, the mean catch of adults per trap increased with the total length of the interface between water and protruding substratum (i.e. the wetted perimeter) and 53% of the variability in the catch per trap was accounted for by this factor. An overall female biased sex ratio was found in the catch. This apparent bias was due to intrusion into the traps of mature females (individuals with mature eggs). After excluding these individuals from the catch only a slight disparity was found in the sex ratio of newly emerged adults. Mature females accounted for 31% of the female catch and 19.6% of the total catch in the pyramidal traps. Hence, estimates of total emergence will be too high, and not just the sex ratio misrepresented, if these individuals are not excluded.

Keywords

stonefliessex ratioexuvia