EEPOET OF THE ENTOMOLOGICAL SECTION 109 



is not much cliaiiee for mosquitoes to breed out in them, but the gudwals, and especially the 

 smaller ones, may not be used for weeks at a time, and a more ideal nursery for mosquitoes 

 than stagnant water in an overgrown gudwal can scarcely be imagined. Each gudwal 

 terminates in a " dead " or " blind " end, that is to say, there is no opening from a gudwal " Weeping" 

 at its extreme end. As a result of this, the water in these " blind " ends is always more or ..^"l.^f"' , 



' •' "blind ends 



less stagnant, and generally bears a covering of green slime. These "blind" ends are 

 necessary to prevent the flow of the water from wearing away the banks. 



Anyone who has had experience in the control of mosquitoes in tropical or sub-tropical 

 countries will be able to understand wliat a source of danger a farm of this kind can be to 

 the inhabitants of the neighbourhood if suitable precautions are not taken. In one instance 

 I attributed all the mosquitoes, which had caused a serious outbreak of malaria in a native 

 village, to a single " blind " end. 



It is generally thought that mosquitoes cannot be controlled on a large artificially 

 irrigated farm except at a very considerable — and frequently in the owner's opinion, an 

 unnecessary — expense. If the matter is gone into carefully, however, it will be found that 

 not only can the mosquitoes be kept in check at a comparatively small cost, but also that it 

 will pay the owner to do so. It must be remembered that when from one to two-thirds of 

 the staff of labourers employed on a farm are suffering from intermittent attacks of fever, 

 they are absent from work for varying periods during the month, and are also often 

 physically unfit for hard and protracted toil during the times when they are supposed 

 to be working. 



The life-cycles of the species of mosquitoes found in the northern provinces occupy 

 about ten days, consequently if all stagnant water on any given area is examined, and, 

 if found to contain mosquito larvae, treated with paraffin or some other larvicide at intervals 

 of a week, no mosquitoes can breed out in that area. It is not always easy to detect 

 mosquito larvas in stagnant water bearing a covering of slime, nor is it possible to approach 

 many of the pools in a gudwal owing to the softness of the mud surrounding them. For Mosquito 

 practical purposes, therefore, it is better to assume that all stagnant water requires to P'''='^*""°ns "°' 



■c^ Jr r ' » o X necessarily 



be treated with parafiin once every week — a great saving of time will be thus effected, expensive 

 A man armed with a stick with a bundle of rag tied at one end, and accompanied by a 

 donkey bearing a tin of pai-aflfin, can walk a long way in a week, paraffining all the stagnant 

 pools he finds on his way, and an intelligent native at a monthly wage of from £E3-4, w'ith 

 a little supervision from the British overseers on the farm, can be trusted to carry out 

 this work. The upkeep of the gudwals is, of course, the duty of the owner — or the tenant, 

 if the land is let out to tenants — and if this is well done, the work of the " mosquito men " 

 will be very considerably lightened. It should be the duty of these men to report to their 

 employer the condition of any gudwal which is either leaky or overgrow-n. 



Paraffin is the larvicide most generally in use against mosquitoes, for it is effective, 

 moderately cheap, and obtainable almost everywhere. A sufficient quantity should be 

 applied to form a film over the entire surface of the water. Another larvicide which has i.arvicides 

 been used with great success by Mr. J. A. le Prince, Chief Sanitary Inspector, Panama 

 Canal Zone,' is made from carbolic acid, resin, and caustic soda prepared in the following 

 way : — 



"Crude carbolic acid containing about 15 per cent, phenol is heated to 212' F., 

 finely pulverised resin is added, and the mixture kept boiling until the resin is all dissolved. 

 Caustic soda solution is then added and the mixture kept at 212 F. for about ten minutes, 

 or until a perfectly dark emulsion without sediment is obtained. The mixture is thoroughly 



' Ros.s, R. 11910), 77«; Prevenliun of Malaria, p. 357 



