L 83
It is in this stored clean water that by far the majority of finds of fasciata larvæ have been made.
As the labour of carrying this water is considerable, the storage receptacle is not frequently emptied and cleansed; more water is simply added to what is already there. The water is also used more economically, the average amount per head being about half that used in Victoria.
The fasciata larvæ 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.
As it was not practicable to empty these barrels, etc., when searching for larvæ, special dippers were made by which samples of the water could be removed for examination.
Experience, however, showed that if the barrel, etc., was full the chance of capturing larvæ was very small, much better results were obtained in receptacles which were more or less empty.
It may therefore be assumed that many well filled barrels and kongs were passed as negative owing to the impossibility of catching the larvæ.
Howard, Dyer and Knab in their well known work “The Mosquitoes of North and Central America and the West Indies” 1912 state (p. 286) "when water is poured from a receptacle inhabited by calopus (i.e., fasciata) larvæ these quickly seek the bottom and their presence may not even be suspected although the vessels be in constant use. They cling so closely to the bottom that unless the jars are tipped up so as to empty them completely, which is not usually done, nearly all the larvæ remain in the jars".
They further state (p. 287) that the first yellow fever commission to Vera Cruz found that, on account of this habit, the larvæ are not easily disposed of by pouring out the contents of a barrel. "When the barrel or other container with thousands of larvæ is approached and slightly agitated the insects disappear rapidly to the very bottom, so that nearly all the water can be dipped out from the barrel without removing more than a few of the larvæ. The barrel may be turned upon its side, and it will be found that about 80% of the larvæ will stay in the few remaining ounces of water."
My experience in Kowloon agrees with these well known authorities and it is therefore, I think, safe to assume that the finds of fasciata larvæ in stored water receptacles (barrels, kongs, etc.) in Kowloon under-estimates the prevalence of these larvæ. The same, however, is probably not true of collections of water found in miscellaneous jars, pots, tins, etc., as in nearly every case these can be completely emptied and the last larvæ collected.
L 83
It is in this stored clean water that by far the majority of finds of fasciata larvæ have been made.
As the labour of carrying this water is considerable, the storage receptacle is not frequently emptied and cleansed; more water is simply added to what is already there. The water is also used more economically, the average amount per head being about half that used in Victoria.
The fasciata larvæ 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.
As it was not practicable to empty these barrels, etc., when searching for larvæ, special dippers were made by which samples of the water could be removed for examination.
Experience. however, showed that if the barrel, etc., was full the chance of capturing larvæ was very small, much better results were obtained in receptacles which were more or less empty.
It may therefore be assumed that many well filled barrels and kongs were passed as negative owing to the impossibility of catch- ing the larvæ
Howard, Dyer and Knab in their well known work “The Mosquitoes of North and Central America and the West Indies 1912 state (p. 286) "when water is poured from a receptacle in- habited by calopus (i.e., fasciata) larvæ these quickly seek the bottom and their presence may not even be suspected although the vessels be in constaut use. They cling so closely to the bottom that unless the jars are tipped up so as to empty them completely, which is not usually done, nearly all the larvæ remain in the jars ".
They further state (p. 287) that the first yellow fever com- mission to Vera Cruz found that, on account of this habit, the larvæ are not easily disposed of by pouring out the contents of a barrel. "When the barrel or other container with thousands of larvæ is approached and slightly agitated the insects dis- appear rapidly to the very bottom, so that nearly all the water can be dipped out from the barrel without removing more than a few of the larvæ. The barrel may be turned upon its side, and it will be found that about 80% of the larvæ will stay in the few remaining ounces of water.'
My experience in Kowloon agrees with these well known authorities and it is therefore, I think. safe to assume that the finds of fasciata larvæ in stored water receptacles (barrels, kongs, etc.) in Kowloon under-estimates the prevalence of these larvae. The same, however, is probably not true of collections of water found in mis- cellaneous jars. pots, tins, etc., as in nearly every case these can be completely emptied and the last larvæ collected.
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