﻿264 L. NICHOLLS — SOME OBSERVATIONS ON THE BIONOMICS AND BREEDING- 



column ii, a, between 7th and 13th of this month, was sufficient to dry up 

 numerous non-permanent breeding-grounds which were under observation in this 

 locality. 



May 1910 (Table III, col. iv, a. b. c.) was a month of extraordinary 

 rainfall, and torrential rain is unfavourable to mosquito development. The 

 roadside gutters, ravines, and rivers became swirling torrents, Avhich repeatedly 

 poured over and swept clean the low-lying marsh-lands. From the nature 

 of the case, many common breeding-grounds could be excluded, and frequent 

 searches over the large water-logged areas, when there were slight abatements 

 in the rainfall, usually failed to reveal larvae of any description. During 

 this and the following month, which had a nearly similar rainfall, I made 

 searches in various quarters on 23 days and only on four days did I discover 

 Anopheline larvae. On three of these occasions they were in small pools 

 near habitations, and effectively protected by a wall or growth of vegetation 

 from the general rush of water ; in the other case, they were found on meadow- 

 land, which was thoroughly overgrown with il guava bush." Probably 

 the adult mosquitos also were destroyed in large numbers by the inclement 

 weather. 



February 1911 (Table III, col. v) was another unfavourable month. After 

 the 10th, numerous pools and swampy, water-logged marsh-lands were found to be 

 teeming with larvae, but the sudden drought dried these up so that few adults 

 appeared. 



The greater part of the year 1911 was very favourable to Anophelines, there 

 being several months with an even and continuous rainfall. The month of 

 November is typical (Table III, col. iii) ; rain fell, but seldom torrentially, 

 on every day in some localities (col. iii, a). At the beginning of this month 

 numerous places were already water-logged, and many Anophelines had appeared. 

 Observations showed a great increase in Amophelines and their larvae, and the 

 dispensary registers recorded an increase in the number of cases of malaria during 

 the next month. 



A still more favourable period occurred after May 1909. Dry weather had 

 obliterated the majority of the breeding-grounds, and was followed by 

 two evenly wet months, which produced great numbers of Anophelines, for 

 the newly formed pools were free from their natural enemies and diseases. 

 (Table III, col. vi). 



Conclusion. 



It is possible to form generalisations on the breeding- places of the Anophelines 

 of a definite country or locality, but at the present time it is inadvisable to do so, 

 as our knowledge concerning their life-struggle and bionomics is still far from 

 perfect. 



All efforts directed to mosquito reduction should be founded, not on generalisa- 

 tions which show theoretically where the insects ought to breed, but upon know- 

 ledge of their breeding-grounds which has been obtained by a prolonged and 

 thorough study of all collections of water which are formed during the 

 year. 



