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INSECTICIDES FOR EXTERNAL BITING INSECTS (FOOD POISONS). 
The arsenical compounds have supplanted all other substances for 
the insects falling under this heading. ‘Two compounds are in common 
use, viz, Paris green and London purple.* The use of powdered white 
arsenic is not recommended, on account of its great liability to scald 
foliage and on account of its color to be mistaken for harmless sub- 
stances. Of the two first mentioned Paris green is the stronger insecti- 
cide, acting quickly, and is less liable to burn foliage. London purple 
has the advantage of cheapness, and, being more finely powdered, 
is kept more easily suspended in water. The former can be had in 
14-pound or larger cans at 20 cents per pound, and the latter at 10 
cents per pound by the barrel. 
WOW TO APPLY ARSKNICALS. 
For all ordinary cases, the use of these poisous in water in the form 
of a spray is advisable. In the cotton fields of the South, where 
prompt and economical action against the cotton worm is essential, the 
dry application of these poisons is more popular. The latter form of 
treatment is feasible also for low-growing crops, such as the potato, 
but can not be employed in the case of orchard and shade trees, and is 
less satisfactory than the use in a spray, in being wasteful, in lacking 
uniformity, and in being more apt to injure foliage. The cheapness and 
rapidity of the dry method gives it a value, however, against the 
cotton worm, and the usual mode of application is as follows: 
The dry method.—A pole 5 to 8 feet long, and about 2 inches in 
diameter with a three-fourths inch hole bored through it within 6 
inches of either end is used. To each end is securely tacked a bag ot 
‘8-07. osnaburg cloth,” 1 foot wide and 18 inches to 2 feet long, so that 


* A third arsenical which promises well, arsenate of lead, has lately been experi- 
mented with by the Gypsy Moth Commission. While not urging that this insecti- 
cide has advantages over Paris green, it is held that it has the merit of showing on 
the leaves, indicating at once which have been sprayed, remains much more easily 
suspended in water, and may be used in large proportions without danger to foliage. 
It has recently been extensively tested at the Department, and a strength as great 
as 1 pound to 2 gallons of water has been used on tender foliage of the peach and 
Osage orange without injury. Good results have attended its use also against the 
imported elin leaf-beetle. The insecticide results were not better, however, than with 
-aris green; but for such sensitive foliage as that of the peach, or where no risk of 
sealding may be taken, I am inclined to believe that it will prove useful. 
This insecticide is prepared by combining, approximately, 3 parts of arsenate of 
soda with 7 parts of acetate of lead. These substances unite chemically and form a 
fine, white powder which remains easily in suspension. As now used by the com- 
mission, 10 pounds of the arsenate of lead are used with 150 gallons of water, 2 
quarts of glucose being added to cause the insecticide to adhere longer to the leaves. 
Prof. Fernald’s experience and our own would indicate that from one-fourth to one- 
half this strength will answer for most larvee—the larvie cf the gypsy moth prov- 
ing to be unusually resistant to the action of poisons. The arsenate of lead costs the 
commission 7 cents a pound wholesale, and glucose $16 a barrel. 
