28 PEEVENTIVE AND REMEDIAL WORK AGAINST MOSQUITOES. 



Mosquitoes breed there in ponds and in chance receptacles of water, 

 but the water in the large canals is so constantly agitated by the pas- 

 sage of boats and by the wind that mosquitoes can not breed, and in 

 the smaller ditches and canals the surface of the water becomes so 

 completely covered with a continuous layer of minute aquatic vege- 

 tation (often of considerable thickness) early in the summer that 

 there is no opportunity for the extensive breeding of mosquitoes. 



Quite recently this idea has been taken up with practical ends in 

 view in regard to antimosquito work in German colonies in Africa. 

 It is stated in a dispatch from Consul-General Richard Guenther, of 

 Frankfort,*^ that the director of fisheries at Biebrich, Mr. Bartmann, 

 had found a duckweed of the genus Azolla to be especially well 

 adapted to this use; and it was at his instance that experiments 

 were made at the malaria station at Wilhelmshaven. It was found 

 that the growth of the plant covered the experimental waters in a 

 short time with a layer of about 6 centimeters, which suffocated all 

 the mosquito larvae below and prevented the living insects from de- 

 positing eggs in the water. Consul-General Guenther states that sev- 

 eral years ago Director Bartmann communicated this method to the 

 mosquito-destroying commission at Eltville on the Rhine, which has 

 used it repeatedly with good success. 



So positive were the statements published in the United States as 

 to the results of Mr. Bartmann's work with Azolla plants that one 

 species has been imported from Europe into the United States and 

 will be experimented upon by the United States Department of Agri- 

 culture and by Doctor Smith, of Rutgers College. The prospects of 

 success, however, are by no means great. One of the German offi- 

 cials who took part in the question of mosquito extermination in the 

 German-African colonies is far from enthusiastic regarding the prac- 

 tical use of this plant, although it has been advertised on all sides in 

 Europe and in this country. In his opinion it may possibly be of 

 some use in special places, but so far as experiments have gone, down 

 to the present day, the plants will not grow in dense or even moderate 

 shade, and therefore they are of no use in the tropical forests where 

 there are large and small pools of water — the very places where it is 

 most needed. Moreover, the Azolla plants do not stand any great 

 cold, nor do they stand short seasons, for which reasons their use is 

 excluded from highland and northern regions. Further, they will not 

 grow in brackish water and can not be utilized along seacoasts, and, 

 still further, in case of drought they all perish and thus necessitate 

 the restocking of dried pools and swamps. 



A short statement regarding the practical use of water plants 

 occurs on pages 1 and 2 of the fourth volume of Theobald's ''Mono- 



a Monthly Consular and Trade Reports, Bur. Manufactures, U. S. Dept. Commerce 

 and Labor, March, 1909. 



