ANOPHELES BREEDING AMONG WATER LETTUCE. 75 



how thick, apphed to the surface of the water in which larvae of M. afri^anus live 

 is absohitely innocuous. He is right, and this is corroborated by our observations 

 upon Mansonia titillans, which is our counterpart to his M. africamis. But nowhere 

 in this article, nor in the preceding one, does he touch upon the control of the Ano- 

 fheles which live in this same habitat, nor does he refer to the use of emulsions which 

 mix with the water and kill by contact, or the destruction of the Pistia by means 

 of sodium arsenite or their removal by boats. 



The logical control is to destroy the habitat. This may be costly and prolonged, 

 and perhaps prohibitive where large numbers of bayous, ponds, cut-oils, etc., exist. 

 If Anopheles alone are to be controlled, spraying with a f)henol-resin soap emulsion 

 every six days will probably be all that is necessary. It may even be effective 

 against the Mansonia. 



Macfie (1917) goes into great detail in his discussion of the favourable oxvgen 

 factor in this Pistia habitat and relates experiments made with certain mosquito 

 larvae which corroborate his contentions. That this exchange of gases is a favour- 

 able one is quite certain. Our common Anopheles have been known to stay on the 

 bottom for five minutes ; if through the presence of green plants they have a more 

 favourable habitat, then it follows that not only may cutaneous respiration be much 

 more prolonged, but the general death-rate among the larvae may be greatly reduced. 

 This death-rate is reduced also because the leaves of the plants protect the larvae 

 from the numerous swimming enemies in the water, and from the hot, direct rays 

 of the tropical sun. 



References. 



Ingram A. & Macfie J. W. S. (1917). The Early Stages of Certain West African 

 Mosquitos. — Bull. Ent. Research, viii, pt. 2. 



Knab, Frederic (1913). Changes in the Mosquito Fauna of Panama. — ^Proc. Ent. 

 Soc. Washington, xv, pp. 41-43. 



Macfie J. W. S. (1917). The Limitations of Kerosene as a Larvicide, with some 

 Observations on the Cutaneous Respiration ot Mosquito Larvae. — Bull. Ent. 

 Research, vii, pt. 3. 



Zetek, J. (1915). Behavior of Anopheles albimanus, Wied., and tarsimaculala, 

 Goeldi. — Ann. Ent. Soc. America, viii, pp. 221-271. 



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