103 



Chidester (F. E.). The Influence of Salinity on the Development of 

 certain Species of Mosquito Larvae and its Bearing on the Problem 

 of the Distribution of Svecies.~New Jersey Agric. Expt. Ski., New 

 Brunswick, Bull. 299, 16 pp., 6 figs. [Received 22nd May 1917.] 



The experimental work described in this bulletin is a continuation 

 of that previously recorded [see this Review, Ser. B, iv, p. 123]. 

 OchlerotatHS (Aedes) sollicitans, ^¥lk., and 0. {A.) cantator, Coq., the 

 two dominant species of salt-marsh mosquitos, were the principal 

 subjects of experiment, though others were carried out on 0. {A.) syl- 

 vestris, Theo., Culex salinarius, Coq., and C. pipiens, L. The effects of 

 the pure salts found in sea water, viz., calcium chloride, magnesium 

 sulphate, potassium chloride and sodium chloride, were studied, as 

 well as the effects of sea water of various degrees of concentration. 

 In the case of Culex pipiens, the larvae that hatched in salt water 

 were unable to withstand the toxic action of salt, but in nature may 

 become acclimatised to the gradually increasing salinity of the water, 

 due to evaporation. 0. sollicitans showed considerable mortality in 

 solutions of low salinity, as well as in those above 21 per cent., but 

 on the other hand, the development of the full-grown larvae was 

 hastened by the hypertonic solution. 0. cantator, Coq., is more 

 susceptible to a high concentration of sea water than 0. sollicitans, 

 since it normally lives in water of 4-6 per cent, lower sahnity. It 

 was found that a 14 per cent, solution kills the majority, and a 24 per 

 cent, solution kills all in one-third of the time taken by the larvae of 

 A. sollicitmis to succumb. All the larvae of Culex pipiens were killed 

 by a 10 per cent, solution, while the second moult larvae of C. salinarius, 

 a salt-marsh mosquito almost identical with C. pipiens, succumbed 

 in water of 8 per cent, salinity. As regards the pupae of 0. sollicitans, 

 it was found that even a 40 per cent, solution of sea water was not 

 strong enough to kill them or to prevent their normal emergence. 

 Field observations show that in large shallow salt pools mosquito 

 larvae may gradually become acclimatised as the salinity increases 

 owing to evaporation. 



As regards the toxicity of the individual salts, calcium chloride 

 was found to be the most toxic, then magnesium chloride, potassium 

 chloride, magnesium sulphate, and lastly sodium chloride. 



Successful attempts, reported in 1911, were made in Virginia to 

 destroy fresh-water larvae by connecting the lake in which they bred 

 with a salt-marsh ; and at New Orleans in 1905 by adding common 

 salt to the open gutters. In the latter case however the final result 

 was the attraction of 0. sollicitans. The action of common salt on 

 the larvae of Stegomyia fasciata has already been noticed [see this 

 Review, Ser. B, ii, p. 84]. 



As a means of control ditching is of the utmost importance, since 

 it quickly drains some areas, bringing the salt water to increase the 

 salinity of permanent pools, and rendering them salt enough to retard 

 or even to check the development of mosquitos. The author also 

 thinks it more than possible that the rise and fall of the waves of the 

 incoming tide may drown the larvae and prove to be a more important 

 factor at high tide than either the presence of fish or the sahnity 

 of the water. 



