158 TKUCK-FAKMItfG AT THE SOUTH. 



comparatively harmless to others, and is more effective 

 on young worms than on older ones of the same species. 

 It is more fatal to the caterpillars of Pieris butterflies 

 than to those of the Plusia moth. The powder does 

 not always kill the worm, but merely so disables it that 

 it falls to the ground, where it will readily become the 

 prey of ants and other natural enemies. 



Pyrethrum seems to owe its virtues to a volatile oil, 

 and its effects are not lasting in the open air. It may 

 be used in the form of dry powder, mixed, if fresh, with 

 from ten to twenty parts of flour, and blown by means 

 of a bellows, or dusted upon the plant. It may also be 

 used in the form of an alcoholic tincture, as a tea or de- 

 coction, or even a mere solution or infusion in water, and 

 applied by means of an atomizer or sprinkler. The 

 fumes of burning Pyrethrum are applicable only in 

 greenhouses or in dwelling rooms, which may be cleared 

 of flies and mosquitoes by its use. 



PLANT-LICE. 



The astounding fecundity of plant-lice (Aphides), and 

 their peculiar habit of attacking stunted plants, have 

 already been mentioned. If the season be not too far 

 advanced, or the plants too large, a badly infested cab- 

 bage should be pulled up, removed from the field, and 

 its place supplied by a clean and healthy one. 



The same valueless applications, with the addition of 

 tobacco water and snuff (tobacco smoke in greenhouses), 

 as in the case of the cabbage-worms, have been also 

 recommended for plant- lice. Pyrethrum may be better 

 than any other, but it would be useless to apply reme- 

 dies to a large, badly infested cabbage, in the hope that 

 it would ever become marketable. If of any effect, its ap- 

 plication might destroy some plant-lice, but I have never 

 carefully examined an infested plant without finding 

 some of the natural enemies of the aphides at work 



