280 Wisconsin State Horticultural Society. 



ing are the most serious ones : 1. The action of the powder, in 

 whatever form it may be applied, is not a permanent one in the 

 open air. If it is applied to a plant, it immediately affects the in- 

 sects on that plant with which it comes in contact, but it will 

 prove perfectly harmless to all insects which come on the plant 

 half an hour, or even less, after the application. 2. The powder 

 acts in the open air, unless applied in very large 'quantities, only 

 upon actual contact with the insects. If it is applied to the upper 

 side of the leaf, the worms that are on the under side are not af- 

 fected by it. 3. It has no effect on insect eggs, nor on pupa3 that 

 are in any way protected or hardened. These disadvantages ren- 

 der Pyrethrum in some respects inferior to arsenical poisons ; but, 

 on the other hand, it has the one overshadowing advantage that 

 it is perfectly harmless to plants or to higher animals; and if the 

 cultivation of the plant in this country should prove a success, 

 and the price of the powder become low enough, the disadvan- 

 tages mentioned above can be overcome to a great degree, by 

 copious and repeated applications. 



In a closed room the effect of Pyrethrum on insects is by far 

 more powerful than out-doors. Different species of insects are 

 differently affected by the powder. Some resist its action most 

 effectually, as very hairy caterpillars, and especially spiders of all 

 kinds ; while others, as all Hymenoptera, succumb a most readily. 

 In no case are the insects killed instantaneously. They are ren- 

 dered perfectly helpless a few minutes after application, but do 

 not die till sometime afterward, the period varying from several 

 hours to two or three days, according to the species. Many insects 

 that have been treated with Pyrethrum show signs of intense 

 pain, while in others, the outward symptoms are much less 

 marked. Differences in temperature and other meteorological 

 changes do not appear to have any influence on the effect of 

 Pyrethrum. 



Pyrethrum may be applied in the dry powder, as a fume ; as 

 an alcoholic extract diluted ; by simple solution of the powder in 

 water, and as a tea or decoction. In applying it as a powder the 

 method most familiar to housekeepers is by means of a small 

 pair of bellows. It is then generally used without diluent, but 



