248 ZOOLOGY FOR MEDICAL STUDENTS chap. 



Mosquito Control 



Malaria — one of the most debilitating and widely spread of all 

 diseases^ and Yellow Fever — one of the most dangerous^ not to mention 

 lesser diseases, being spread entirely by the bites of mosquitos it follows' 

 that keeping down the numbers of these insects to the minimum, 

 in regions where natural conditions favour their existence, is an insistent 

 need. Its successful accomplishment may indeed be an essential condi- 

 tion to the continued existence of a white community in a particular 

 locality. 



It is in warm climates where mosquitos carry on their life-history 

 throughout the year that their control is especially necessary. In regions 

 of wide-spreading tropical swamps it is of course out of the question to 

 think of exterminating mosquitos entirely, but even in such places much 

 may be done to diminish their numbers within actual human settle- 

 ments owing to the fact that normally mosquitos do not travel any great 

 distance. 



What renders the problem of mosquito control a practical one is the 

 fact that the earlier and normally much longer portion of the life-history 

 is passed in the form of a larva (Fig. 107, 1) or pupa (Fig. 107, II,) which 

 lives in water but has to breathe air by means of a pair of stigmata, 

 situated in the pupa of Anopheles and in the larva and pupa of Culex at 

 the end of projections from the body. The line of action indicated there- 

 fore is to take measures (i) to ensure, if possible, that bodies of water 

 suitable for the larvae and pupae shall not exist in the immediate 

 neighbourhood of human habitations, and (2) should such be in existence 

 to render them uninhabitable by the mosquito larvae and pupae. The 

 latter object may be attained most easily by covering the surface of the 

 water with a thin film of oil which blocks up the stigmata and renders 

 it impossible for the young mosquito to breathe. The oiP may be 

 sprayed on to the surface of pools two or three times a week, or allowed 

 to drip from a tin or drum with a small hole plugged with cotton waste. 



OiUng is merely temporary in its effects and in the case of permanent 

 settlements more definitive measures are required. All unnecessary 

 collections of water which may afford suitable breeding grounds for 



1 Any cheap oil. Its efficiency is said to be much increased by the addition 

 of " larvacide " prepared in the following way. Carbolic Acid (150 gallons) is 

 heated to nearly boiling point and Resin (150-200 lbs.) stirred in till dissolved. 

 Solution of Caustic Soda (30 lbs. in 6 gals, water) is then added and the whole 

 stirred for about five minutes. If a little of the larvacide is added to a little 

 water it should emulsify : if it does not do so it should be heated further until 

 it does (Jacobs). 



