Life histories of lotic mayflies (Ephemeroptera) in an Ozark stream: Instar determination and voltinism

Life history studies were conducted on four commonly occurring species of m ayflies from an Ozark stream in Missouri. A multivariate statistical techni que, using a suite of In-transformed body measurements of Stenonema mediopu nctatum (McDunnough) (Ephemeroptera: Heptageniidae) nymphs, discerned at le ast nine instars during the sampling period. This technique provided greate r resolution in discriminating among instars than using raw data or head ca psule widths alone. Further, S. mediopunctatum was determined to be univolt ine in these streams, as were Caenis hilaris (Say) and C. latipennis Banks (Ephemeroptera: Caenidae). Tricorythodes curvatus Alien (Ephemeroptera: Lep tohyphidae) apparently was multivoltine.