374 



THE AGRICULTURAL NEWS 



NovEMBEE 30, 1918. 





MOSQUITO CONTROL, 

 la the publications of the Imperial Department of 

 Agriculture for the West Indies, attention has from 

 time to time been drawn to the importance of mosquito 

 control in tropical countries, but, as was pointed out in 

 the editorial of the previous number of the Apri- 

 cultural News, there is need for more sustained 

 and instructed work in this direction. The UV-.? 

 India Committee Circular, September 19, 1!>1m, 

 points out that Dr. Sambon, who visited these islands 

 some years ago, thinks they are very backward in 

 the measures taken to control mosquitoes of all kinds. 



A lecture by Dr. W. Dwight Pierce, the leader of 

 the class for the study of the Entomology of Disease, 

 Hygiene, and Sanitation — the formation of which was 

 noticed in the Agricultural News, July 27, 1918 — 

 has been received at the Head Office of this ] )epart- 

 ment. The lecture is reproduced below. At the end 

 will be found a brief list of recent publications on 

 the subject. 



Probably more money and more concentrated eflfort have 

 been devoted to mosquito control throughout the world than 

 to the control of any other disease-bearing inaects. We may 

 discuss the essential elements of mosquito control topically. 



PEEVKNTIO.N OK M0.>(^UH0 BKEKDIN(.. 



By far the most important measures to be taken are 

 those which prevent the breeding of mosquitoes. In this 

 class of measures we therefore have to deal in some manner 

 ■with water. If general mosquito control is sought, it is not 

 essential to ascertain the species breeding, but when large 

 communities or armies are to be protected .against disease- 

 bearing raos(Hiitoes, time may not permit of general mosquito 

 control, but may necessitate particular attention to the 

 haunts of the disease bearers. 



srOLlING. 



The preliminary measures to be taken, therefore, are the 

 organization and training of scouting parties designated 

 primarily to search out the breeding haunts of these .sjiecies, 

 and to report them to the details or squads designated for 

 control work. The scouts must be trained entomologists, 

 skilled in the knowledge "i mosouito haunts. They must 

 examine the water in all receptacles in and around buildings, 

 and in discarded vessels. They must seek out all puddles, 

 hoof prints, wagon ruts, tree holes, ditches, and streams, and 

 carefully examine these. A chart should be kept showing 

 the location of all water, and this can be marked in variuus 

 ways to indicate the species present. Coloured pin markers 

 on a wall chart ;ire very serviceable. A field ch^rt would 

 have to he marked otherwise. 



I.EVEI.LINi; A.NIi hi.i.i.m; watkr holks. 



Hquads of men may be detailed to look after the level- 

 ling of ground where water is apt to' gather and remain, and 

 to fill up small puddles, pools, hoof tnarks, ruts, etc., which 

 serve no useful purpose, and where drainage is inadvisable. 

 Holes in trees should be be filled up with cement. Stumps 

 which hold water should be grubbed out, and the stump 

 holes filled. In rocky streams, pot holes in the rocks often 

 breed many mosquitoes. If possible, the rrick should be 

 jtrooved, or removed, or the holes may be filled with cement. 



DITCHING AND CLEAKI.Ni; STKEAMS AND SWAMPS. 



Other detail,> may be designated to clear stream beds, 

 and drain lowlands. Spring lands, bogs, and swamps furn- 

 ish an abundance of mosquitoes, and are the first places to 

 receive the attention of the ditching squads. Ditches must 

 be constructed to carry off standing water. These should be 

 laid out by an engineer. The ditches must have straight 

 banks, and even bed, and must be kept free of vegetation. 

 Sometimes it is necessary to spray the vegetation along the 

 ditches with oil, and burn it All burrow pits and puddles 

 caused by grading roads and railways should be connected 

 up by a ditching system, or filled. Flowing streams usually 

 have trees along their sides. Uader such trees water is 

 often trapped to form a quiet undisturbed place for mosquito 

 larvae. Trees must not. grow on the edge of the bank. Tree 

 roots must be removed from the stream. Any kind of vege- 

 tation growing in the bed of a stream favours mosquito 

 breeding, as it affords some protection against natural 

 enemies, and prevents adequate artificial control. The 

 stream bed must be clear of vegetation. The banks 

 must be straightened, and constructed without overhanging 

 ledges. There should be no obstruction to the free flow 

 of the stream. If it meanders, a new and straight 

 course ought to be constructed, and the old course filled. 

 Springs which furnish good water should be boxed and pro- 

 tected. Le Prince and Orenstein very ably describe in their 

 book, the methods of clearing streams and propagation areas 

 in jungles in the tropics. 



CLEARING OF ^^'EED•FILLED BAYS AM> LAKES. 



Large bodies of water in which dense growths of grass 

 and weeds occur furnish great problems in many camps; and 

 in tropical countries, especially where feasible, it is often 

 desirable to furnish the mos(juito squad with two motor boats, 

 and with submarine saws or other implements for cutting and 

 removing vegetation. If this cut vegetation remains, it aggra- 

 vates the situation. Large lily leaves, which when alive 

 furnish no place for breeding, will often, when dry, foim cups 

 of water, in which mosquitoes breed prolifically. 



DRAINAGE. 



The construction of drainage systems should preferably 

 be done by a sanitary engineer who understands the mosquito 

 phase of the problem. The main ditches should be con- 

 structed first, and the laterals added later. Sometimes, where 

 weed jirowth is rapid, it is desirable to have a double, 

 parallel, series of ditches, one only operating at a time 

 during heavy rains, with the idea that the idle ditch can be 

 cleaned and shaped up. It is essential that the floor level of 

 the ditch affords no opportunities for puddles to form after 

 the greater part of the water has passed ort'. In permanent 

 ditching it is .sometimes feasible and advisable to line the 

 ditch with concrete, or at least to line the bottom. Weep 

 holes should be made at sufficient intervals to cany into 

 the drain water which gathers on the outside of it. Branch 

 ditches should enter the main ditch at an acute angle, c r oti a 

 curve. At the Junction of bridges there should be a splash 

 wall to confine the water within the ditch. Potholes formed 

 in dirt ditches should be filled up after rains with gravel or 

 stone and tamped hard (see I.e Prince and Orenstein, 

 pp. 137-44). 



In certain soils, where seepage water outcrops abun- 

 dantly on hillsides, it is .sometimes practicable to install an 

 intercepting tile drain ige system. The tiles are laid at right- 

 aDgle> to the flow of the seepage at the highest .seepage water 

 level, with a space of one-eighth to a quarter inch between 

 joints. The grade of the trench bottom must be true. 

 Tiles must not be located on soft mud where tliey miy sink. 



