27 



Usinger: Introduction 



■ 



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Intro, fig. 36. Lining o ditch with concrete and sodding the upper banks to increase effectiveness 

 and reduce maintenance costs, a, before; b, after (U.S.P.H.S., C.D.C. photo). 



areas using tile or buried poles. Breeding place's may 

 also be eliminated by filling with a bulldozer or by 

 diking and dewatering with pumps. 



In brackish waters such as are found in the salt 

 marshes, drainage ditches may suffice, but more 

 often tidal action requires that other measures be 

 used. Dikes may be constructed with tide gates or 

 automatic siphons to hold back the salt water at high 

 tide and permit drainage outward at low tide. 



Biological control has long been a solution to 

 mosquito breeding in local areas. The top minnow, 

 Gambusia affinis, is ideal for this purpose and can 

 be introduced into ornamental pools (intro. fig. 37) 

 or even into cisterns and other unlikely bodies of 

 water. Mosquito fish have been distributed so widely 

 that they may be found in almost any body of water or 

 a supply can usually be had by telephoning the near- 

 est mosquito control agency. Gambusia are not needed 

 in garden pools if goldfish are present and are not 

 fed excessively. 



Mosquito larvicides are considered as emergency 

 measures or temporary means of control, yet larvicid- 

 ing has and probably will continue to occupy a large 

 part of the time of mosquito control crews. Progress 

 in this field has been so rapid during and since World 

 War II that generalizations are likely to be misleading 

 and are certain to be dated. 



The principal materials in use at the present time 

 are: oils, either alone or as solvents for organic 

 poisons; chlorinated hydrocarbons such as DDT and 

 related compounds; and organic phosphates. The 

 toxicity of various chemicals was tested with colo- 

 nized larvae of Culex quinquefasciatus Say by Isaak 

 (1952) with results as shown in table 2. 



Intro, fig. 37. Stocking a garden pool with mosquito fish, 

 Gambusia affinis (U.S.P.H.S., C.D.C. photo). 



Of the larvicides tested, EPN was the most effective 

 followed by Parathion, Aldrin, colloidal Aldrin, 

 Heptachlor, Dieldrin, DDD, DDT, Q- 1 37, chlordane, 

 lindane, and toxaphene in that order. Field applica- 

 tions are made at concentrations that seem ridiculously 

 low by prewar standards. Formerly, 20. gallons of fuel 

 oil or 20 pounds of Paris green dust were applied per 

 acre of water surface, at great expense and effort. 



