PLANTS AND MOSQUITO CONTROL MATHESON 423 



Table 3. — Aquaria experiments ioilh Chara fragilis to test egy deposition 



An examination of the table brings out a most important fact — 

 that wherever there is decay and dying of the Chara oviposition by 

 Culex species took place almost immediately. In experiments 1052- 

 22 and 24 the Chara maintained a vigorous growth throughout the 

 season and no oviposition took place. In those experiments in 

 which considerable decay took place at the beginning, oviposition 

 is recorded and most of the larvae which hatched from the first 

 Qg^ masses matured. Those that hatched from egg masses deposited 

 when the Chara was regaining vigor failed, in most cases, to mature. 

 In those aquaria in which growth did not take place (1052-28, 42, 

 43, 44, and 45) oviposition was exces.sive throughout the season and 

 immense numbers of adults emerged. Yet despite this density of 

 adults no oviposition took place in those aquaria containing a vigor- 

 ous growth of Chara. Why mosquitoes do not oviposit on water 

 containing a vigorous growth is not known. It may be added that 

 no oviposition took place in our outdoor tubs or wooden troughs 

 where Chara growth was vigorous. Oviposition always began when 

 decay started and became excessive as the decay increased. 



These and other laboratory experiments appeared so promising 

 that a survey of the local area was undertaken to discover if pools, 

 ponds, lakes, etc., where Chara flourished were free from mosquito 

 breeding. Numerous more or less isolated ponds were found with 

 vigorous growths of Chara and in practically every case mosquito 

 breeding did not occur. These results were so encouraging that 

 attempts were made during the seasons of 1928 and 1929 to introduce 

 Chara fragilis into as wide a variety of known breeding places as 

 possible. This was done and several of these introductions were 

 studied during 1928 and 1929. In order to understand the problems 



