Flight direction in some rocky mountain mayflies (Ephemeroptera), with observations of parasitism

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Abstract
Adult mayflies (Ephemeroptera) were sampled using sticky traps at several locations along a Rocky Mountain stream. Eight genera were collected, of which imagos oiBaetis spp and Rhilhrogena hageni were most common. Baetis was represented almost exclusively by females and flight direction was significantly in the upstream direction. In R. hageni both males and females were included. Females appeared to fly into clearings or downstream, whereas males showed no directionality, or a downstream bias. This difference in adult flight direction may be partly explainable by the greater amount of downstream drift in Baetis relative to R. hageni. Finally, mermithid nematodes were found to be frequent parasites of Baetis but not of R. hageni causing total absence of eggs in infected females.