Drumming behavior and life history notes of a high-altitude colorado population of the stonefly Isoperla Petersoni Needham & Christenson (Plecoptera : Perlodidae)

Late instar nymphs and adults of a Colorado Hudsonian zone population of Is operla petersoni Needham and Christenson were studied during the summer and early fall months of 1998, when stream temperature ranged from 3.3 degrees C to 8.9 degreesC. Early and middle instar nymphs were absent from July to October, and nymphs attained maximum size in mid-August during the 2nd week of adult field presence, suggesting a univoltine-slow life cycle. Nymphs w ere carnivorous and fed primarily on chironomid larvae. Adults were present from August to mid-October, with peak numbers of adult males and females o ccurring in mid-September and late September, respectively. Fecundity of fi eld-collected females averaged 94.1 +/- 45.15 eggs per female in September (N = 81) and decreased to 85.2 +/- 57.6 in October (N = 12). Drumming duets were 2-way (male-female), and female answers followed male calls (nonoverl apped) or began before completion of the male call (overlapped). Male calls averaged 11.1 +/- 2.09 beats and female answers averaged 6.2 +/- 2.99, wit h mean intervals of 118 and 58 ms, respectively. The average number of fema le answer beats increased from 5.3 +/- 2.56 when duets were nonoverlapped, to 6.6 +/- 3.08 when overlapped.