Description and theoretical considerations of mate finding and other adult behaviors in a Colorado population of Claassenia sabulosa (Plecoptera: Perlidae)

Adult behaviors of a Colorado Gunnison River population of Claassenia sabulosa (Banks) are reported. Synchronized emergences began in late July 1992 and early August 1993; each emergence lasted approximate to 2 wk. Eighty-nine percent of nymphs crawled out of shallow water onto emergent stones near the shoreline for transformation, predominantly on dark nights beginning at nightfall. Males emerged significantly earlier in the night than females, their molting times were significantly shorter, and they began immediately searching near the shoreline on isolated stones partially exposed above the water surface. Male male searching consisted of circling and scrambling over high areas and angular sections of the emergent rock encounter sites. Males encountering a molting female guarded her and began attempting copulation when her genitalia became exposed. Copulations lasted approximate to 62 s, and males subsequently guarded females to delay or reduce further matings by other males. A few unguarded, individual females were observed mating up to 9 times with as many as 5 males. Most females were mated for the 1st time before hardening. Both sexes were active only during the 2-h period just after dusk. When not engaged in mating, they scurried over the water surface between emergent stones and the shore. At all other times, they remained inactive under stones or debris on the stream bank, typically within 1 m of the shoreline. Females with extruded egg masses scrambled over the water surface between emergent stones, washing eggs directly into shallow water. Females were never observed flying and could not be induced to fly. Drumming, by males, did not appear to be a primary requisite for mate finding. Evolution of mate finding behaviors in relation to drumming and other behaviors is discussed, and a paradigm for evolution from a drumming-assisted mate locating method to a search-intensive, encounter site specific method is proposed for this population.