No. 3.] Calcutta Municipal Water. tg3 



garden of the Royal College. These were the insects that had been 

 attracted by the bungalow lights on the previous evening, a fact that 

 indicates that the flies are not ephemeral but live for more than one 

 day. Several small clouds of the flies were noticed outside the 

 Pettah Station, but I was informed that they had not been so trouble- 

 some during the last few days. During the south west monsoon the 

 flies are carried by the prevailing wind to the north and north- 

 eastern shores of the lake, involving the Fort and the Pettah in the 

 nuisance ; while the Colpatty and Slave Island bungalows are 

 affected during the prevalence of the north-east winds. All stages 

 and ages of the insects were observed to be present at the same 

 time. There is apparently a constant succession of broods throughout 

 the year. 



SUGGESTIONS FOR REMEDIAL MEASURES. 



In dealing with this pest we are fortunate in having a nearly 

 complete knowledge of the life history of the insect, and it will be 

 possible to attack it at each of the principal stages of its existence. 



The eggs, as noticed above, are laid in the water, anchored to 

 some solid substances which will retain them at the surface, ensuring 

 them the amount of light and air necessary for their development. 

 As this part of the lake is kept free from floating weeds by a system 

 of contracts, it follows that the deposition of the eggs must be con- 

 fined to the margins of the water. The removal and destruction of 

 all floating rubbish and herbage growing in the water at the margins 

 of the lake will ensure the destruction of an enormous number of 

 eggs. This will not prevent the subsequent deposition of fresh 

 batches of eggs on the banks. But from my observation that float- 

 ing sticks form a favourite point of attachment for the egg-masses, 

 I think it would be possible to trap the bulk of the eggs by laying 

 down, in the water along the margins, bamboos lightly covered with 

 brushwood. The eggs would be deposited on these during the 

 night. The following morning the bamboos should be lifted out 

 and left on the bank to dry. The heat and drying action of the sun 

 would kill any eggs deposited on these traps. The bamboos would 

 be returned to the water each afternoon at about 5 o'clock. To 

 reduce the available breeding places, the smaller unoccupied islets 

 might be removed. 



The larvae, living on the surface of the mud and being independent 

 of gaseous air, would be unaffected by any applicatio n of kerosene 

 to the surface of the water. The restriction of the eggs to the 

 margins of the lake fixes a limit to the feeding grounds of the larva» 



