Drumming Behavior of Four Western Nearctic Isoperla Species (Plecoptera: Perlodidae)

Abstract

The drumming behaviors of four Isoperla species from the western Nearctic region are described for the first time. All have monophasic male calls and sequenced male-female exchanges. Isoperla miwok Bottorff & Szczytko males call with a mean of 5.7 beats and 25.3-ms beat intervals. Male-female drumming extends up to six-way exchanges. Isoperla acula Jewett males call with a mean of 4.1 beats and 356.8-ms beat intervals; male-female exchanges are two-way. Male calls appear to be produced by abdominal tapping and rubbing of the substrate. Drumming in I. acula differs greatly from that of the closely related I. mormona Banks, apparently helping these sympatric species maintain reproductive isolation. Isoperla adunca Jewett males call with a mean of 6.1 beats and 137.8-ms beat intervals. Isoperla bifurcata Szczytko & Stewart males call with a mean of 6.4 beats and 47.2-ms beat intervals; male-female exchanges are two-way. Some California Isoperla have similar male calls, but drumming is species-specific for the entire male-female behavior. Considerable variability in drumming behavior exists between and within the five species complexes of western Nearctic Isoperla. As a group, Isoperla displays many derived drumming traits.