Feeding of Simulium hargreavesi Gibbins larvae on oedegonium algal filaments in Ghana.

On a dam spillway of earth and rocks at Nalerigu, in Northern Region of Ghana, huge numbers of larvae of Simulium hargreavesi Gibbins were found feeding exclusively by grazing on filaments of the green algae, Oedegonium inconspicuum Him and Oedegonium moniliforme Wittrock, and on organic debris trapped among the filaments. More than 200 midguts were dissected. The narrower species, O. inconspicuum (3.4–5 μ in diameter), was found in the gut in lengths between 100 and 1500 μ, mostly in the 165–500 μ range. The wider species, O. moniliforme (8.5–10 μ in diameter), ranged in length in the gut from 65–1000 μ, but those over 500 μ were few. The findings by other investigators of blackfly larvae feeding on filamentous algae arc reviewed, along with reported deterrent effects of such algae. The possibilities of control of grazing species through absorption, adsorption, and residual retention of insecticides by the filaments are also discussed. The gross appearance of S. hargreavesi masses on the filaments, and the 2 species of Oedegonium in dissected midguts, are illustrated by photographs.