Depressant Effect of Moonlight on Activity of Aquatic Insects

Abstract

INVESTIGATIONS by Waters¹, Müller^2–5, and Wickett⁶ have conclusively demonstrated the diurnal periodicity of downstream drift of aquatic insects and other invertebrates. Prior to these investigations, Moon⁷ had shown that the nocturnal activity of aquatic insects is much greater than that observed during the day. Very little data are available to demonstrate whether these activity-levels are circadian rhythms or whether they are a direct response to the level of light intensity. Beeton⁸ observed a depression of the vertical migration of the freshwater shrimp, Mysis relicta, due to increased moonlight. Waters¹ suggested that the magnitude of the nocturnal drift rate may be, in part, a function of moonlight. The following data appear to support Waters's contention.