The Biosystematics of Isonychia Bicolor (Walker) of the Finley Creek, Missouri

Date of Graduation

Spring 1981


Master of Science in Biology



Committee Chair

Steven Jensen


Isonychia bicolor (Walker) was collected from riffles in the Finley Creek, Missouri, from April 1979 to June 1980. The imago, subimago, and larvae were described and some taxonomoic characters were compared with other species. A single egg mass hatched in 20 days and the head capsule width of the first instar was 0.138 mm. The larval head widths of field samples ranged from 0.364 to 1.976 mm. The size frequency diagrams indicate asynchrony and overlap of generations. Larval dry weight was a highly significant exponential function of head capsule width as: Weight (mg) = .7872 x Head width (mm) 3.9418. Larval density and biomass increased during summer and winter and decreased during spring and fall emergence peaks. Emergence, subimago flight, mating swarms, and oviposition were described. Mating swarms were observed in spring and fall and the head widths of the imagos were significantly larger in the spring. Final instar larvae were present throughout the summer and subimagos were collected during July and August. The data indicate an asynchronous univoltine life cycle.

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© David Michael Sullivan