58 



THE AGRICULTURAL NEWS. 



February 22, 1918. 



INSECT NOTES. 



SUGGESTIONS FOR MOSQUITO CONTROL. 

 IN A WEST INDIAN ISLAND. 



(Concluded.) 



The elimination of mosquitoes from the vicinity of the 

 dwelling depends on the proper draining or filling in of all 

 breeding places, or stocking with 'millions' all tanks and 

 cisterns, and the removal of all bosh and trees which 

 f oroish shelter for the adult mosquitoes. 



All waste water from the dwelling house should be carried 

 away in properly constructed drains, and no water should be 

 thrown out on to the ground in such .a way as to leave any 

 pools or puddles, or even muddy spots. 



At the estate referred to there is a large concrete cistern 

 which contiins a permanent supply of water. This is stocked 

 with 'millions,' and if it is kept fairly clean of algae and other 

 water plants, it should not be a source of mosquitoes. 



A pond below the house is also well stocked with fish, but 

 the cattle come to drink at this pond, and the margin is cut 

 up by the feet of the animal. There is some danger in this, 

 since the smallest amount of water is liable to breed mosqui- 

 toes in these depressions. I recommend that this pond be 

 fenced, and the animals all watered at the trough across the 

 road. The margins of the pond should be carefully graded, 

 and no foot prints or other depressions allowed to exist there. 

 No bush or overhanging grass or weeds, should be allowed to 

 grow on the margin of this pond. 



The drain, which takes the overflow from the pond, 

 crosses the road and runs down into the savannah, should be 

 properly constructed, and the bottom cemented. The culvert 

 tinder the road should be made of large drain tiles with a 

 smooth inner surface, and set at a good angle, so that no 

 water can stand in it. Beyond the road, the drain which is 

 badly washed should be filled to a proper gradient, and 

 provided with a concreted surface for some distance. 



The trough at which the cattle are watered should be 

 provided with a proper overflow pipe. A smooth cobbled 

 pavement around the trough would prevent any foot-prints of 

 animals leaving any depressions near, where water can stand in 

 them, and the well from which the water is drawn should be 

 provided with a properly constructed curb, and securely 

 covered, either by means of a light wooden cover, or with wire- 

 mssh , to prevent the entrance of mosfjuitoes. 



Any escaping water either from the sugar works or from 

 the still should pass at once into a properly constructed 

 concrete drain, and be carried off'. The final dispasition of 

 such water and of the overflow water from the ponds and from 

 the watering trough must >ie a matter for special consideration. 

 If it can be allowed to escape on to the surface of thesavannab 

 at some distance from the buildings, in such a manner that it 

 will not provide breeding places for mosquitoes, that might be 

 allowed. It is likely, however, that a properly constructed 

 drain "may have to be provided to connect with the drainage 

 system in the sandy soil nearer the beach. The concreting of 



such a drain would be an cspcnbive matter, and it might suffice 

 to provide a well-made trench with clean sides and with 

 smooth bottom, which cr.uld be oiled at intervals by hand or 

 by means of an automatic arrangement. 



For this purpose ordinary kerosene is useful, but it is 

 costly, and it evaporates quickly. Crude oil evaporates more 

 .slowly, and it is likely that Trinidad fuel oil would serve for 

 this purpose. If such oil were supplied from time to time the 

 applications might be made at iptervals of from ten to 

 twelve days by means of a knapsack sprayer, using a nozzle 

 of the Bordeaux type, discharging a fine solid stream with 

 some force into the water. The oil would be , broken up on 

 striking the water, and form a film on the surface. 



The automatic arrangement consists of some device which 

 contains the oil and supplies it to the water in one of two 

 ways. One way of doing this is by^means of an automatic 

 dropper. A kerosene tin or similar receptable is fixed over 

 the drain with a cork or spiggot or other device for dropping 

 the oil drop by drop on the water below. In a drain 

 carrying a small amount of water with a slow moving current 

 ten to twenty drops per minute would be sufficient. The dis- 

 tance apart at which such droppers might be placed would 

 have to be determined by experiment. Another way consists 

 in fixing a box or bag of sawdust saturated with oil in such a 

 manner that the water would pass through it carrying out a 

 small quintiy of oil. By these means, and by the utmost care 

 to prevent any standing water even in the smallest quantities 

 the vicinity of the buildings on the estate in question ought 

 to be freed from al! breeding places of mosquitoes. The 

 depression in the pasture near the coco-nut trees should be 

 kept free from water after the drains are completed, and 

 another source of infestation thus removed. 



The malaria mosquito is a weak flyer. It flies only short 

 distances except when it is able to gain shelter in the foliage 

 of trees or bush or in long grass. In favourable situations 

 these insects fly from plant to plant, and, especially when 

 travelling with the wind, are able thus to cover some distance. 

 They are said not to travel more than a mile fiom their 

 breeding place and not more than 'JOO to 300 yards at a 

 single flight from one shelter to another. 



The removal of che bush on the hill side to the east, 

 and the substitution of a close cropped pasture would probably 

 deprive the mosquitoes of their means of approach from the 

 swamp on that side. Any other swamp within, say, ^mile 

 would need to be taken into consideration for similar 

 treatment. It is .said that a dense belt of tree growth acts 

 as a barrier to the dispersal of mosquitoes." It might be 

 worth while to consider a belt of trc^s along the margin of 

 swamps some distance from the buildings, with carefully 

 kept pasture on the near side of this. 



A word may be added with regard to the cattle pens 

 and the houses of the labourers in relation to their proximity 

 to the dwelling houses. Mosquitoes attack practically all 

 warm blooded animals. If mo.squitoes are present, and can 

 get to cattle pens and st;ibles, they wil' take shelter there, 

 and find food in abundance in the blood of the animals. 

 From such situations they may travel to the manager's house. 



.\t least 400 to .'iOO yards should separate the labourers' 

 huts from the dwelling house, as their children are almost 

 universally carriers of malaria in a malarious district, even 

 though they show no signs of sufl'ering from the malady. 

 The labourers should be compelled to maintain the most 

 scrupnh'us sanitation about their cabins, and no water should 

 be thrown about in such a way as to allow mosquito breedio". 

 I'roper drainage should yyt irranged for. 



H.A.B. 



