The giant Salmonflies of the Western mountains are legendary for their proclivity to elicit consistent dry-fly action and ferocious strikes.
A new parthenogenetic mayfly (Ephemeroptera:Ephemerellidae:Eurylophella Tiensuu) oviposits by abdominal bursting in the subimago
David H. Funk, John K. Jackson, Bernard W. Sweeney
Eurylophella oviruptis new species is described and illustrated from female larvae and reared subimagos and imagos collected from swamp streams in North Carolina, USA. Several key morphological characters in the larva place this new species in the Eurylophella temporalis group. Genetic comparisons with other eastern North American Eurylophella revealed a fixation of alleles unique to E. oviruptis at 4 of 19 allozyme loci. Eurylophella oviruptis appears to be obligately parthenogenetic because no males were observed in the field or laboratory and eggs taken from subimagos and imagos hatched parthenogenetically (mean hatch rate = 79%). Abdomens of 60% of subimagos reared in the laboratory burst along the ecdysial line of the first 3 tergites immediately after transformation to the subimago at the water surface. Abdominal bursting ruptured the oviducts, released most of the eggs into the water, and left the subimago trapped on the water surface with a large, inflated midgut protruding from the split in the tergites. Subimagos that did not burst (40%) flew from the water surface, molted to the imago on the 2nd day following emergence, and then, without having mated, extruded a ball of eggs that was released into the water. Dissections of E. oviruptis and 5 other species of mayflies showed that inflation of the mayfly gut normally occurs at 3 stages: emerging larvae inflate prior to and during the molt to the subimago, subimagos (particularly males) inflate further at the imaginal molt, and female imagos inflate even further at oviposition. Gastrointestinal inflation in mayflies maintains full abdominal distention that might facilitate flight. Abdominal bursting in E. oviruptis subimagos appears to be the result of gut inflation well beyond the amount normally associated with this stage. The evolutionary significance (predation, dispersal, demographics) of oviposition by abdominal bursting is discussed.