426 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 31 



canadensis, whereas the Chara pool contained . an extremely small 

 number of larvae. 



The woodland 'pool. — The woodland pool (pi. 7, fig. B) is a 

 large pothole which usually maintains a water supply till late 

 August or September. Here breed Aedes sthnidans, A. excruciajis, 

 A. fitchii, and A. purictor. The larval density is usually very high, 

 and immense numbers of adults swarm during the summer in the 

 surrounding woodlands. Near by are numerous breeding places for 

 these species so that if Chara would grow and maintain itself in 

 this pothole we would have an excellent opportunity to test its 

 efficiency. The introductions were made on April 14 and 21, 1928. 

 During the summer of 1928 the Chara maintained a considerable 

 growth, but in 1929 none could be found. Though the experimental 

 pool had a high larval density in 1928, there were very few larvae 

 in 1929. Unfortunately the near-by potholes, where there was a high 

 larval density in 1928, had comparatively few in 1929. In fact, this 

 whole woodland area, which usually swarmed with mosquitoes dur- 

 ing the summer, had very few during the season of 1929. The reduc- 

 tion was probably due to a salamander {Diemictylus mridescens) , 

 which swarmed in all the pools during 1928 and 1929. This sala- 

 mander has been shown to be a voracious feeder on mosquito larvae. 



Though numerous other introductions were made, none of them 

 could be followed up in detail. Several new introductions were made 

 in 1929, and I have hopes that some of these may prove more success- 

 ful. Our failures are due, in all probability, to our ignorance about 

 the biology and cultivation of the Characeae. Though I have worked 

 with only one species, Chara fragilis, other investigators have em- 

 ployed several other species sometimes with apparent success but 

 unfortunately more often with failure. However, this line of work 

 is directing more and more students to study the underlying factors 

 of larval food, selective breeding habits of mosquitoes and the water 

 conditions which induce or prevent mosquito breeding. 



OTHER AQUATIC PLANTS 



Little experimental work has been done with other aquatic plants. 

 Zetek (1920) reports that in the Panama Canal Zone anophelines 

 were found breeding in the floating islands and other masses of 

 water lettuce {Pistia stratiotes). In Brazil, Bachmann (1921) 

 found that mosquitoes appear to avoid Pistia stratiotes, MyHophyl- 

 Uum hrasiliense, and Lemna. He states that MyriophylliuTn hrasil- 

 iense is being planted along the streams at points where breeding 

 places have been cleared away. In the southern United States, Bar- 

 ber and Hayne (1925) find that anophelines breed amidst water 

 hyacinth {Piaropis crassipes). 



