Seasonal Drift of \u3ci\u3eLethocerus Americanus\u3c/i\u3e (Hemiptera: Belostomatidae) in a Lake Superior Tributary

Drifting adult Lethocerus americanus were captured and retained by an inclined-screen smolt trap during two field seasons in the Bois Brule River, Wisconsin. Seasonal peaks of drift occurred in spring for 4 weeks following ice out and in autumn for 7 -8 weeks from mid-September through ice formation, and may have continued under ice cover when our gear was not operated. These findings are consistent with the known movement pattern of these insects to fly from lentic habitats to streams to overwinter but also suggest longitudinal movement via drift, perhaps to reach specific overwintering sites. Drift was significantly correlated with declining water temperatures in 1989 but not in 1990. Most drift occurred at water temperatures less than 12°C. There was no correlation between drift and river discharge. Drift rates were consistently low with a maximum by volume of 9 animals per 10,000 m3