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



Classification of breeding-grounds. 



The collections of water which have to be studied for the purposes of a 

 mosquito survey may be conveniently divided into four classes : — 



(1) Non-permanent, (2) altered permanent, (3) permanent, and (4) miscel- 

 laneous. 



I. Non-permanent waters. 



Under this heading I include those collections of water which are formed after 

 heavy or continuous rainfall ; they can be further sub-divided into : — 



(a.) Marshy land, which tends to become water-logged, but the water quickly 

 disappears after a few dry days, though some deeper pools may remain. This land 

 is the greatest producer of Anophelines in this island (PI. VI, fig. 1). It will 

 be found that busk and hills, or other objects, afford protection in each case. 

 An illustration is given (PI. VI, fig. 2) of a pasture land which is low-lying 

 and situated in open country on the outskirts of a village ; though it frequently 

 becomes water-logged and contains numerous pools, larvae have never been 

 found in forty-seven searches in the more open parts. It will be seen therefore 

 that these marshy places must afford some protection for the adults and larvae 

 before mosquitos can thrive in them ; and while these insects may be entirely 

 absent from the exposed portions of such localities, yet a careful investigation of 

 obscure corners and sheltered nooks may reveal their presence in some numbers. 



The following is an exaggerated example of this type of ground : — 



It was a four-acre, water-logged, neglected cemetery, much overgrown with 

 grass and bush, and with numerous high trees, the whole being surrounded by a 

 high wall. The place had never been drained, except by a few gutters which 

 were blocked up and overgrown. Around all the tumuli were depressions from 

 which the earth had been obtained for the purpose of forming them ; apart from 

 this the ground was naturally very uneven. During and just after rainy 

 weather Anophelines were bred out from this ground in vast numbers, and 

 malaria was rampant in the immediate neighbourhood. 



(b.) Small pools. These may be small isolated pools partly overgrown by 

 vegetation, or muddy hollows in protected situations, but without immediate 

 protection from the elements. The former are common along road-side gutters, 

 the latter are frequently formed by man in his agricultural or building work. I 

 have known a herd of pigs to produce a large number of such holes when 

 wallowing in soft mud in wet weather. One of these which contained numerous 

 larvae is illustrated (PI. VII, fig. 2). It was filled with opaque water, due to 

 much suspended mud and decomposing matter, and the larvae lying on the 

 surface were very apparent. 



(c.) Large surface undulations. The water which collects in such situations 

 tends to last a very short time in this island, and is relatively unimportant. 



II. Altered 'permanent ivaters. 



Numerous waters are unsuitable for Anophelines until they are temporarily 

 altered by the agency of the elements or man ; they may be subdivided into : — 



(a.) Pools altered by heavy rains. In a number of pools I have been 

 unable to find larvae except after heavy rains. The water has poured through 



