68 THE STEGOMYIA SURVEY IN HONG KONG. 



in areas which are densely built over, either in the houses themselves or in their 

 immediate vicinity. It is noted as an important point that it was unusual to find 

 this Stegomyia breeding in miscellaneous receptacles, such as old jars, tins, etc., as 

 recorded by observers elsewhere, even though these breeding places w^ere subjected 

 to specially careful and prolonged search both by Dr. Thomson and Dr. Macfarlane. 

 Such receptacles were nearly always occupied by the larvae of S. scutellaris, while 

 S.fasciata showed a very marked preference for the clean water stored for household 

 purposes. With the exception of a few licensed premises, none of the Chinese houses 

 in Kowloon have water laid on, and all water for drinking, cooking, etc., has to be 

 carried from stand-pipes in the street and stored in the kitchen or yard in barrels, 

 jars, or pails. As the labour of carrying this water is considerable, the storage recep- 

 tacle is not frequently emptied or cleansed. The water is also used more economi- 

 cally, the average amount per head being about half that used in Victoria. The larvae 

 have therefore plenty of time to develop, and owing to their well known habit of going 

 to the bottom when the water is disturbed, they are not likely to be taken out when 

 water is removed for cooking or other purposes. Experience showed that if the 

 receptacle was full, the chance of capturing larvae was very small ; it may therefore 

 be assumed that many well-filled barrels, etc., were passed as free from mosquitos 

 owing to the impossibility of catching the larvae. The observations of Messrs. Howard, 

 Dyar and Knab in America are quoted to show how closely the larvae can cling to 

 the bottom of a vessel, for even if a barrel be turned upon its side, it will be found 

 that about 80 per cent, of the larvae will stay in the few remaining ounces of water. 



Dr. Macfarlane considers that the results so far obtained in Kowloon would appear 

 to indicate that if the storage of clean water could be completely done away with by 

 laying on a continuous tap supply in the houses, the chief breeding places of S.fasciata 

 would be destroyed ; provided that no cisterns are allowed unless they are completely 

 protected. 



The miscellaneous jars in houses and backyards in Victoria have been very 

 thoroughly examined, with the result that only in three cases have Stegomyia fasciata 

 larvae been taken, and these in widely separated localities ; so that such containers 

 are even less frequented by this species than in Kowloon. Tap water is laid on in 

 all houses in Victoria, the supply being continuous for about seven months in the year, 

 while for the remaining five months it is intermittent, but never less than two hours 

 a day. A relatively very large number of storage vessels are kept in use during the 

 intermittent period, but the great majority of them are not utilised during the con- 

 tinuous supply. At the time of Dr. Macfarlane's inspections water was plentiful, and 

 any storage barrels in use were too full to be examined properly. In Hong Kong 

 harbour two police collectors made 1,500 visits to the junks and Chinese cargo 

 lighters, but they failed to find any S.fasciata larvae. 



Dr. Macfarlane is to be congratulated upon the very thorough and painstaking 

 mosquito survey which he has carried out. 



