Semivoltinism, Seasonal Emergence, and Adult Size Variation in a Tropical Stream Mayfly (Euthyplocia hecuba)

Abstract

Life history characteristics of the stream mayfly Euthyplocia hecuba (Hagen) (Polymitarcyidae:Euthyplociinae) were studied over a 4-yr period in two tropical streams (Rio Tempisquito and Quebrada Marilin) draining primary evergreen forest in northern Costa Rica. Larvae burrow in the substratum of the stream, living under small to large cobbles that are firmly embedded in the stream bottom. Euthyplocia hecuba is sexually dimorphic and one of the largest mayflies of Central America, with maximum larval size of 149 mg (dry mass) for females and 35 mg for males. Mature female and male larvae are about 40% larger in Q. Marilin relative to R. Tempisquito. Subimagoes emerge about 1 h before dawn (∼0400 h); the molt to the imago (or true adult stage) occurs ∼20 min later. Adult emergence and reproduction occurs mainly between June and November. Females mate and then oviposit in riffle areas just before dawn, with the time period gradually changing from 0446 and 0507 h in June to 0508 and 0529 h in October. We fou...