INLAND DISPERSAL OF ADULT AQUATIC INSECTS

1. Adult caddisflies (Trichoptera) and mayflies (Ephemeroptera) were l ight-trapped on summer evenings along the Detroit River and Lake St. C lair, near Windsor, Ontario, Canada. Light traps were located at the s hore and at increasing distances inland up to 5 km, and were operated simultaneously for 2 h following sunset. Catches of five species of ca ddisflies of the family Hydropsychidae (Cheumatopsyche campyla, Cheuma topsyche speciosa, Hydropsyche hageni, Hydropsyche phalerata, Macroste mum zebratum) and the mayfly Hexagenia (Ephemeridae) were used to exam ine inland distribution. 2. Inland dispersal was limited: catches of c addisflies declined at a greater than exponential rate with increasing distance from shore. Mean dispersal distance from the shoreline range d from 650 to 1845 m. Smaller caddisfly species dispersed shorter dist ances than larger caddisflies and Hexagenia. 3. Inland distribution of adult caddisflies exhibited considerable interspecific variation: dis tribution was inconsistent among trials for Hexagenia, possibly owing to timing of collections in relation to periods of: peak emergence. 4. Sex ratios of caddisflies were female biased at most sites. No consis tent bias was observed for Hexagenia. Different inland distribution pa tterns were observed for males and females. The differences appeared t o reflect species-specific reproductive strategies.