REPORTS OF AUXILIARY SOCIETIES. 297 



Among insecticides, using the word in its ordinary and literal meaning, we 

 must include everything which destroys insects at any and every stage of their 

 multiform existence. 



The horticulturist himself who has no scruples against using a muscular thumb 

 and forefinger, makes an insecticide of no mean value. The insectivorous 

 birds and mammals, such as the skunk and badger, must also find their place 

 in the list. To these are to be added the insects themselves which prey on 

 others, or their eggs or larvae. Then, there are the fungi, plants of low orga- 

 nization, which attack and destroy enormous numbers of insects in their imma- 

 ture stages. And we must also mention extremes of weather, heat and cold, 

 drought and moisture, which no doubt aid in keeping our insect pests under 

 control, and probably have much to do with the almost entire absence of some 

 species during certain years. 



In addition to this varied list of insecticides, drawn from such different 

 sources, we have those substances which are applied by man himself to the 

 plants infested by injurious insects. The list of these is a long one, but it can 

 be readily divided into two classes, mineral and vegetable poisons. 



MINERAL INSECTICIDES. 



Among the mineral or inorganic insecticides the arsenical compounds take 

 the first rank, from their cheapness and general utility. The objections to 

 their use are, first, they are dangerous to man and the domestic animals; sec- 

 ond, they also injure plant life when used in too great quantity; third, they 

 affect the stomachs only of insects that bite off the outer parts of leaves and 

 buds. Insects which bore deep into leaves or steins to suck the juices are not 

 much affected by these poisons. Three forms of arsenic are used, Paris green, 

 London purple, and white arsenic. The most commonly used is Paris green. 

 It costs forty cents per pound in Ann Arbor at the present time. The propor- 

 tions used are one tablespoonful to four gallons of water; or one pound of 

 Paris green to twenty pounds of flour. The insects for which it is usually 

 applied, are potato beetles, currant worms, cabbage worms, canker worms 

 and codling moths. 



London purple is claimed by C. V. Riley and other experts to be in general 

 as effective as Paris green. The proportions used are half a pound to fifty gal- 

 lons of water; or half a pound to eighteen pounds of flour or other dry sub- 

 stance. It is used for the same insects as Paris green. London purple costs in 

 Ann Arbor twenty cents per pound. 



The third form of arsenic is white arsenic. This is worth experimenting 

 with. C. V. Riley gives this formula: Boil one pound of white arsenic and 

 one pound sal soda in a gallon of water until the arsenic is dissolved; then use 

 one quart of this to forty gallons of water; use for the same insects and in the 

 same way as Paris green. White arsenic can be bought in Ann Arbor by the 

 quantity at eight cents per pound, and sal soda at five cents. White arsenic is 

 more dangerous than either of the other forms of arsenic because it is color- 

 less in solution and may easily be taken for something harmless. It should be 

 colored by soluble Prussian blue. 



Paris green, from its high price, is more apt to be adulterated than the others, 

 which are so cheap that they are hardly worth the trouble of adulteration. 

 The fear that such a common use of forms of arsenic would poison the ground 

 finally, seems to be considered without foundation by scientific men. 

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