380 MOSQUITOES OF NOETH AMERICA 



the best of the larvicides, namely, the petroleum products, was discredited by 

 the authors in question. 



PERMANGANATE OF POTASH. 



In the last few years many substances have been experimented with, both in 

 the United States and in other parts of the world, and there has been from time 

 to time a newspaper notice, or a series of newspaper notices, of some new sub- 

 stance which careful experimentation has shown to be of little or no service. 

 In this way the use of permanganate of potash received much advertising in 1900, 

 but, as one of the writers has elsewhere pointed out, as a result of careful ex- 

 perimentation it was found that small amounts of the chemical have no effect 

 whatever upon mosquito larvae. They were, however, killed by using amounts so 

 large that, instead of using a handful to a 10-acre swamp, as had been stated in 

 the newspapers, at least a wagon load would have to be used to accomplish any 

 result. Moreover, after the use of this large amount and after the larvae were 

 killed, the same water 24 hours later sustained freshly hatched mosquito larvae 

 perfectly, so that even were a person to go to the prohibitive expense of killing 

 mosquito larvae in the swamp with permanganate of potash, the same task would 

 have to be done over again a few days later. 



SULPHATE OF COPPER. 



In 1904 a publication by the Bureau of Plant Industry of the U. S. Depart- 

 ment of Agriculture, on the use of sulphate of copper against algae and other 

 microscopic plant life, put certain newspaper men on the wrong track and a 

 number of articles were published making the erroneous statement that the De- 

 partment of Agriculture recommended sulphate of copper as a perfect remedy 

 against mosquito larvae. So widely was this alleged discovery heralded that 

 careful experiments were at once made by the Bureau of Entomology, by Doctor 

 Smith, of New Jersey, by Doctor Britton, of Connecticut, and by other ento- 

 mologists, with the result that the substance was found to be of very slight 

 value as a larvicide, and of really no practical value whatever. 



CERTAIN PROPRIETARY COMPOUNDS. 



Several proprietary mixtures or mosquito compounds have been prepared and 

 placed on sale for the purpose of destroying mosquito larvae. A number of these 

 have been brought or sent to one of the writers for experimentation but, consider- 

 ing the cost, none of them has been of as great practical value as petroleum. 

 In his report on the mosquitoes occurring in the State of New Jersey, 1904, 

 Doctor John B. Smith describes a number of experiments with substances of 

 this kind, notably with certain soluble carbolic acid and cresol preparations, 

 with chloro-naphthaleum, and with phinotas oil, and in his report for 1907 he 

 gives the results of certain experiments with a substance known as " killarvas." 

 It is not necessary, however, to consider any of these substances in this con- 

 nection except to state that phinotas oil has met with considerable use, since it 

 forms a milky compound with water which settles through a pool and destroys 



