PLANTS A-RB MOSQUITO CONTROL, — MATHESON 419 



Barber (1924) in the United States, Fisher (1924) in Panama, 

 Buxton (1924) in Palestine, Swellenfjrebel (1925) in Holland, Reyne 

 (1924) in Surinam, Vasilev (1925) and Tarnogradski (1925) in 

 Russia, and Hamlyn-Harris (1928; 1929) in Australia would indi- 

 cate that the Characeae have little, if any, effect on mosquito breed- 

 ing. Blow (1924) reports little mosquito breeding in Madagascar 

 where species of Chara abound, but in 1927 he states that the 

 Gharophyta {Characeae) possess no larvicidal qualities. Hacker 

 (1922) reports doubtful results in the Federated Malay States. Such 

 conflicting results would indicate that we know very little of the 

 underlying factors that induce or prevent mosquito breeding. Every 

 worker is fully aware that certain types of aquatic situations induce 

 mosquito breeding, whereas other or even almost identical situations 

 do not bring about breeding. In other words, we have what may 

 be called the selective breeding habits of each species. What are 

 the factors that control or govern such selective breeding habits? 



Early in 1923 I was impressed by such conditions in central New 

 York and began a certain line of investigation in an attempt to 

 answer some of these questions. The discovery of a permanent 

 spring- fed pool (pi. 5, fig. 1) richly carpeted with a growth of 

 Chara fragilis * enabled me to plan a line of work which might 

 promise some results. In this pool, and similar ones since discovered, 

 no mosquito breeding took place. It seemed ideal as a mosquito 

 habitation. Farmhouses were located near by, and cattle grazed in 

 large numbers in the surrounding pastures, so that the adults had a 

 ready source of blood. Why, then, do mosquitoes fail to breed here? 

 A few preliminary experiments made in 1925 seemed to indicate that 

 the carpeting of Chara fragilis might be the inhibiting factor. Noth- 

 ing further could be done till the spring of 1927. At that time I 

 attempted to obtain answers to the following questions: (1) Does 

 this species of Chara have an inhibiting effect on larval develop- 

 ment? (2) Will mosquitoes oviposit readily on 67iflra-filled pools, 

 and if they do what becomes of the larvae that hatch out? (3) If 

 Chara has an inhibiting effect on the development of the larvae what 

 is the causal agent? (4) Or, if the presence of Chara inhibits ovi- 

 position what are the factor or factors involved? (5) What is the 

 food of mosquito larvae? 



To answer the first question a long serious of experiments was con- 

 ducted in aquaria in our greenhouse (pi. 4, fig. 1). The aquaria 

 were stocked with Chara fragilis^ and the larvae of various species 

 of mosquitoes were added from time to time. Water from a near-by 



* This species is now detorminod as Chara vulgaris Linn. 

 102992—32 28 



