APHIDES. 201 



aphis are more or less injured by cold, but still they 

 cannot be entirely killed by freezing, as we have 

 reason to know from experience in growing plants 

 in frames, where the temperature fell as low as 

 six or eight degrees below zero. In such cases 

 many aphides were destroyed, but enough sur- 

 vived to start a new brood as soon as the weather 

 became favorable. 



The almost universal remedy against aphides 

 under glass has, up to the past few years, been 

 tobacco. Fumigation has been the principal 

 method followed, the ordinary tobacco stems 

 being used for the purpose. Probably in some 

 sections fumigation with tobacco will continue to 

 be used, as it is undoubtedly the simplest and 

 cheapest method of combating these pests. 



We have already pointed out, however, the 

 serious objections to the continued use of tobacco. 

 This is especially the case in certain regions where 

 the use of tobacco is more apt to bring on 

 spot than in other sections. Where it is necessary 

 to use tobacco, great care must be exercised, and 

 the grower should never wait until the insects 

 have accumulated in numbers, otherwise the 

 smoke will have to be made so strong that injury 

 to the plant in one form or another is sure to fol- 

 low. Light fumigations, given at regular inter- 

 vals, will probably hold both kinds of aphides in 

 check, but aside from the objections already 

 mentioned there are others of a serious nature 



