Great Basin Naturalist


Emergents of Pteronarcys californica, Calineuria californica, and Hesperoperla pacifica were captured with replicated emergence traps at 3 sites along the banks of Rock Creek, Montana. Pteronarcys emergence in early June was short (88% of individuals in 6 d) and attained rates of 5 m−1 d−1 (shoreline distance) and cumulative densities up to 19 m−1 yr−1. Calineuria emerged synchronously (89% in 9 d) 2 wk later at densities up to 7 m−1 d−1 and 40 m−1 yr−1. The less numerous Hesperoperla (5 individual m−1 yr−1) had a longer emergence period partially coinciding with Calineuria. Median males of Pteronarcys and Calineuria emerged 2–3 d before median females; protandry was not significant in Hesperoperla. Sex ratios were female-biased in Pteronarcys and Hesperoperla but male-biased in Calineuria. Size trends through emergence were very weak although females showed a greater tendency toward larger size early in emergence.