277 



THE LIMITATIONS OF KEROSENE AS A LARVICIDE, WITH SOME 



OBSERVATIONS ON THE CUTANEOUS RESPIRATION OF 



MOSQUITO LAI{\AE. 



By J. W. Scott Macfje, M.A., D.Sc., 

 We-sf African Medical Skiff. 



Of all the measures designed to effect a reduction in the number of mo.squitos 

 " oiling," or the application of kerosene in one form or another to collections of water 

 in the neighbourhood, is I suppose the favourite. The popularity of this measure is 

 no doubt an indi(;ation of its general efliciency. and as it is a remedy that can and should 

 be employed by the individual as well as by the Sanitary Autliorities, it has become 

 familiar to every dweller in the tropics. This familiarity has, I believe, led to an 

 exaggerated confidence in its efficacy. 



When Ross (1899) in Sierra Leone first elaborated the method as a public health 

 measure, it was witli a view to the destruction of malaria-carryijig mosquitos and 

 those Culicines that breed in and near human habitations. So great has been the 

 success following its adoption in certain conspicuous undertakings, that the general 

 public has come almost to believe that by " oiling " it should be possible to banish 

 mosquitos entirely from towns and stations, and surprise is expressed if the Sanitary 

 Authorities fail to effect this reduction. It is too often forgotten that many localities 

 aie ill-suited for the application of this method, that many surfaces of water cannot 

 be efficiently oiled, and that by no means all the species of moscpiitos that bite man 

 breed close to houses. 



.A.t Accra, the capital of the ( iold Coast Colony, '" oiling " with crude kerosene is 

 carried out bv the Sanitarv Authoiities in a most thorouf{li manner, and a snreat 

 reduction in tlie number of mosquitos in the houses is said to have resulted. Never- 

 theless mosquitos are still very far from rare, and the reasons for this are not difficult to 

 trace. Accra is a wind-swept town, and oil applied to a surface of water, no matter 

 how carefully^ is soon driven to one side, leaving the more exposed parts with only a 

 broken film, through which the larvae may safely come to the surface. Even a very 

 large quantity of oil in proportion to the area fails to maintain an unbroken film for 

 the long period that, as will be shown later, many larvae can .sur\-ive without rising 

 to the surface. Accra is also a sunny and relatively dry town, and evaporation is 

 rapid and prejudicial to the success of oiling. 



More impoi-tant than these reasons, however, is the fact that the majority of the 

 mosquitos found in the houses, and which therefore e>pecially concern man, are of 

 species that do not breed in the innnediate vicinity of dwellings. As has been shown 

 elsewhere. t!ie larvae most frecjuently found in the compounds are those oi Stefjotnyia 



