194 Indian Museum Notes. tVol. V. 



It is improbable that they would wander very far from their native 

 spot. A zone of some ten yards from the bank, all round the lake, 

 would practically cover the sphere of action of the larva. The re- 

 moval of the mud, to a depth of only six inches, along this marginal 

 zone, will effectually destroy the myriads of larva now breeding 

 there, A shallow dredging, repeated twice or thrice during the 

 year, will be much more effective than deeper dredging at longer 

 intervals. It will be necessary to remove the oozy surface mud 

 only. The larvae will not thrive in the firmer gravelly or sandy mud. 

 The insects inhabiting, as they do, merely the surface layer of the 

 mud, it may be necessary to contrive some modification of the 

 ordinary m ethod of dredging, to prevent the dispersal of this super- 

 ficial layer during the operation. Possibly some form of hand 

 dredging might be employed. I am confident that a judicious 

 system of dredging, on the lines here suggested, will practically 

 remove the nuisance or, at any rate, very greatly mitigate it. 



The greater number of the pupae would be destroyed by the same 

 measures that have been suggested for the removal of the larvae. 

 But in this stage the insect is also vulnerable at a different point, 

 namely, at the time when it rises to the surface of the water prepara- 

 tory to the liberation of the fly. A film of kerosene on the water at 

 this time would kill any of the pupae with which it came in contact* 

 and would certainly prevent the successful emergence of any flies. 

 If it is decided to give this plan a trial, the application should be 

 made in the evening, shortly before dusk. The simplest and most 

 effective way of applying the oil would be by trailing a rope, covered 

 with rags or tow soaked in kerosene, along the surface : the ends of 

 the rope being attached to two boats which would be rowed along the 

 margins of the lake at a suitable distance from each other. The rope 

 should be periodically recharged with oil. 



The adult flies are notoriously attracted by light, and might, 

 perhaps, be trapped by bonfires or lighted chulahs placed along the 

 edge of the lake. But 1 am of opinion that this measure would not 

 really repay the cost. An enormous number of flies might, however, 

 be slaughtered on Dhobies' Island and at other places where they 

 are known to rest during the day, by spraying the grass with a 

 mixture of kerosene and water. 



I am most sanguine of profitable results from the employment of 

 the system of dredging suggested above. 



Royal Boa.' A NIC Gardens, Feradeniya, 



. ztgust loth, igoi. 



E. Ernest Green, 

 Government En tomologist. 



