39 



Hodgson (E. C.)- Malaria in the New Province of Delhi. — Ind. Jl. 

 Med. Research, Simla, ii, no. 2, October 1914, pp. 405-415, 4 charts, 

 7 maps, 6 pis. 



Twelve species of Anophelines are recorded from the flat dry country 

 round Delhi, which, in the cold weather, appears to be a most im- 

 probable place for mosquito breeding. In August and September, 

 however, ib is covered with large sheets of shallow water in the midst 

 of which coarse grass and crops are growing, and in some of these pools 

 larvae, mainly of A. culicifacies, are so numerous as to make a black 

 rim, a foot wide, visible as much as twenty or thirty yards away. 



The species concerned are : — Anopheles rossi, the larvae of which 

 were found in small numbers as early as the beginning of April, 

 but only began to show a large increase in July, continuing in enormous 

 numbers in October, and gradually dying out in November, though 

 a few were still found even as late as December. Its breeding grounds 

 were multitudinous both in the city and outside it, and during the mort- 

 soon, it far outnumbered all the other Anophehnes. It was never 

 found infected with malarial parasites and its relative frequency in 

 the various areas bore no relation to the amount of malaria. Its 

 favourite breeding grounds are small muddy pools near houses and 

 shallow pools in the Bela. 



A. culicifacies was found throughout the entire year, though its 

 numbers were much increased during the monsoon and for some time 

 after it. Its favourite breeding grounds were : — Shallow temporary 

 pools on the Bela ; slow-moving streams and pools in the bed of 

 shallow watercourses, some of which only had water running in them 

 when rain w^as actually falhng ; in the main Western Jumna Canal 

 and its tributaries, especially when the flow of water had been cut off 

 at the canal head and the water remaining in the canal was slowly 

 moving along its weed-grown bed. The important point about the 

 favourite breeding grounds of this species is that the water must be 

 fresh, not too deep, and be changed slowly but regularly. This specieis 

 was twice found infected with malarial parasites by Adie in 1911, and 

 three times by the author in 1912. 



The larvae of A. stephensi were never found in large numbers in any 

 part of the district, but their universal distribution in wells, not only 

 in the city but throughout the country-side, made their numbers 

 considerable in the aggregate. During the monsoon, especially in 

 September, larvae were sure to be found in three out of four wellsr 

 The method adopted for capturing the larvae in this position was a 

 shght modification of that of Christophers. In the modified method, 

 the hoop carrying the net was let down into the water not horizontally 

 but at an angle. The greatest care was taken not to cause any splash- 

 ing, because, as pointed out by Bently in Bombay, A. stephensi larvae 

 are extremely active and can, when frightened, remain below the surface 

 over fifteen minutes. Instead of pulhng the net straight up from 

 the spot at which it has sunk, the whole water surface is skimmed as' 

 far as possible and larvae captured at other parts of the surface than 

 that disturbed by the lowering of the net. A. stephensi larvae were 

 also found in fair numbers in the pools on the Bela. One very unusual 

 breeding place for this mosquito was found in April 1913, viz., a 

 slowly-moving shallow stream. In this position the larvae werei 



