The life history and larval generic character development of Malenka bifurcata (Claassen, 1923) (Plecoptera: Nemouridae) in an Oregon summer-dry stream

Abstract

This is the first report of the life history and ontogenic larval development for any of the 11 North American species of Malenka. Concurrent monthly collections of larvae, and adults from emergence traps, were made over 15 years from an intermittent Oregon stream. Data from 2002–2007 collections were used for analysis; 97 males and 163 females were taken from emergence traps, and the head capsule widths of 192 larvae were measured. Counts of antennal and cercal segments, branching and growth of anterior thoracic (AT) gills, wingpad development, setation changes, and other morphological developments were recorded for an array of different sized larvae. Voltinism was variable, and the life history was complex with spread emergence and larva sizes. Progressive development of all studied characters occurred from the smallest field sampled larvae (0.36 mm hcw) to pre-emergent size. Antennal and cercal segments and gill branches nearly doubled in number, gill branch length doubled and typically the anterior-most branch branched secondarily, wingpads increased to 1.05–1.35 mm, intercalary cercal hairs appeared, and individuals could be sexed in latest instars.