THE INFLUENCE OF DROUGHT UPON MOSQUITO LIFE IN SURREY. 207 



Culex pipiens. 



Normal conditions. — As larvae and pupae ; abundant principally in water- 

 troughs, rain-water barrels and other artificial water collections. As adults ; abun- 

 dant in houses, cellars, stables, etc. 



Conditions during drought. — As larvae and pupae ; relative numbers reduced, 

 but actual numbers in available breeding-places often increased. As adults ; easily 

 found in considerable numbers, but not so numerous as in normal years. 



Culex pipiens being a species that largely makes use of artificial water collections 

 used by man, it follows that often these collections are maintained by him in spite of 

 dry weather, and thus Culex pipiens is not at so great a loss to find breeding-grounds 

 as are the less domestic mosquitos. 



Culicella morsitans. 



Natural conditions. — As larvae and pupae ; commonlj/ found in certain wayside 

 ditches and in rain-water barrels. As adults ; quite common in out-houses, stables, 

 cellars and outside latrines, but never found in large numbers at a time. 



Conditions during drought. — As larvae and pupae ; scarce and now only found in 

 one rain barrel kept supplied with water artificially, and in one instance found in a 

 shallow well ten feet below ground. As adults ; none observed for many weeks. 



Culicella fumipennis. 



Normal conditions. — As larvae and pupae ; common in certain wayside ditches. 

 As adults ; frequentty found on the walls in out-houses and stables. 



Conditions during drought. — As larvae and pupae ; unobtainable. As adults ; 

 unobtainable. 



Finlaya geniculata. 



Normal conditions. — As larvae and pupae ; abundant in the water-containing 

 holes in a variety of trees. Often associated with the larvae and pupae of Anopheles 

 plumheus. As adults ; sometimes observed to attack human beings while they are 

 in the woods, though not very often seen. 



Conditions during drought. — As larvae and pupae ; unobtainable since middle of 

 June. As adults ; unobtainable, and not observed in the woods since beginning 

 of June. 



Soon after the tree-holes had begun to dr}' up generallv, numerous larvae and 

 pupae of Finlaya geniculata were collected from several holes that still contained 

 water, and these were brought to the laboratory for experiments on their develop- 

 ment in waters giving different reactions. Many were placed under conditions 

 that highly favoured development and emerged as large and active mosquitos. 

 They were at first kept in a cage in the laboratory and fed upon dates and human 

 blood in an attempt to obtain ova from them, but while all the females partook 

 of an ample diet, fertilisation apparently would not take place under caged conditions, 

 even when there were about an equal number of active and healthy males in associa- 

 tion. In the hope of getting ova from them under natural conditions, the whole 

 batch of mosquitos was carefully captured in tubes and taken to the vicinity of 

 a beech-tree in which the tree-holes were kept full of water, and there released. 

 Possibly on account of the fact that the water in the holes was besieged by insects 

 of all kinds (see under Anopheles plumheus), no eggs were laid, nor were any of the 

 released mosquitos seen again. 



(4183) q2 



