Morphology of Early Instar Larvae and Life History of Ephoron eophilum (Ephemeroptera : Polymitarcyidae)

Abstract

The life history of a burrowing mayfly, Ephoron eophilum ISHIWATA, was studied in the Kinu River, Ibaraki Prefecture, Japan, which a congener E. shigae (TAKAHASHI), inhabits sympatrically. E. eophilum had a univoltine life cycle. First instar larvae were found during the long period from April to July, and adults appeared from July to October, which is in contrast to the more syncronous life history pattern of E. shigae. Another distinct difference between these two species is the diurnal timing of the emergence of imagos and subimagos : E. shigae emerged after sunset, while E. eophilum emerged at early dawn. E. eophilum females had fewer (352-1863) larger (0.25 mm in diameter) eggs than E. shigae females which had as many as 634-3420 eggs 0.16 mm in diameter. Hatchings of E. eophilum were larger in body size than those of E. shigae, and had well developed mandibles which may be adapted to life in harder clay stream beds. © 1998, The Japanese Society of Limnology. All rights reserved.