Inland dispersal of adult aquatic insects


ZSOLT E. KOVATS Golder Associates, 1011 Sixth Avenue SW, Calgary, Alberta, Canada T2P 0W1


1. Adult caddisflies (Trichoptera) and mayflies (Ephemeroptera) were light-trapped on summer evenings along the Detroit River and Lake St. Clair, near Windsor, Ontario, Canada. Light traps were located at the shore and at increasing distances inland up to 5 km, and were operated simultaneously for 2 h following sunset. Catches of five species of caddisflies of the family Hydropsychidae (Cheumatopsychecampyla, Cheumatopsychespeciosa, Hydropsychehageni, Hydropsychephalerata, Macrostemumzebratum) and the mayfly Hexagenia (Ephemeridae) were used to examine inland distribution.

2. Inland dispersal was limited: catches of caddisflies declined at a greater than exponential rate with increasing distance from shore. Mean dispersal distance from the shoreline ranged from 650 to 1845 m. Smaller caddisfly species dispersed shorter distances than larger caddisflies and Hexagenia.

3. Inland distribution of adult caddisflies exhibited considerable interspecific variation: distribution 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 consistent bias was observed for Hexagenia. Different inland distribution patterns were observed for males and females. The differences appeared to reflect species-specific reproductive strategies.