Effects of DDT Mosquito Larviciding on Wildlife. Part III. The Effects on the Plankton Population of Routine Larviciding with DDT.

The use of DDT as an anopheline larvicide has caused considerable concern in some groups because of the potentialities of destruction of other, more desirable forms of life in ponds and lakes. A series of studies has been undertaken to determine the extent, if any, of such damage. Among the organisms under consideration, fish are of prime importance to wildlife and sportsman interests, and might be affected in any of several ways: direct damage by poisoning and killing, reduction or destruction of desirable food organisms, or ecological changes resulting in unfavorable environmental and growth conditions. Ecologically, there are three groups of important fish-food organisms in areas commonly larvicided: the fauna of the bottom, the plankton organisms, and the surface and shallow-water forms. The present paper, the third in a series reporting on the effects of DDT larviciding on wildlife, is a report on the plankton, which is the chief food source for several species of fish and most fish fry. The present study was begun in the spring of 1945 on ponds located in the vicinity of Savannah, Ga. The ponds were all shallow and small, being typical of ponds in which breeding of Anopheles quadrimaculatus occurs.