[Upstream migration of Philopotamus montanus (Trichoptera)]

Imagines of Philopotamus montanus were sampled by light-traps and by hand at four sites along the Kaltisjokk in Swedish-Lappland. The samples were quantitatively and qualitatively analysed and compared. They differed in the following points: 1. There were many more imagines at the mouth of the stream than in the upper reaches. 2. At the mouth of the stream the percentage of the females was about one third compared with the samples from the upper reaches. Most of these females were immature, whereas most of the females from the upper parts had already laid their eggs. Mature females, which were ready for the first oviposition were distributed uniformly along the stream. 3. The proportion of mature females caught in the light-traps was twice that caught by hand. Immature females and females which had already laid their eggs were less numerous in the light-traps than in the hand-catches. 4. During the ten-day period of the investigation the differences between the samples from the four sites decreased. 5. With the light-traps most of the insects were caught during the day-time (6-22h). The sex ratio changed with the time of day. In the morning males dominated the catch, and in the afternoon females. 6. The reliability of the methods is discussed and the hypothesis is put forward that mature, egg-bearing females migrate upstream.