"law of supply and demand."

_Wheat plant-lice_ form collectively the third insect pest destructive
to wheat, of which it is reported that "the annual loss occasioned by
wheat plant-lice probably does not fall short of two or three per cent
of the crop."

HAY AND FORAGE CROPS.--These are attacked by locusts, grasshoppers, army
worms, cut-worms, web worms, small grass worms and leaf hoppers. Some of
these pests are so small and work so insidiously that even the farmer is
prone to overlook their existence. "A ten per cent shrinkage from these
and other pests in grasses and forage plants is a minimum estimate."

COTTON.--The great enemies of the cotton-planter are the cotton boll
weevil, the bollworm and the leaf worm; but other insects inflict
serious damage. In 1904 the loss occasioned by the boll weevil, chiefly
in Texas, was conservatively estimated by an expert, Mr. W.D. Hunter, at
$20,000,000. The boll worm of the southwestern cotton states has
sometimes caused an annual loss of $12,000,000, or four per cent of the
crops in the states affected. Before the use of arsenical poisons, the
leaf worm caused an annual loss of from twenty to thirty million
dollars; but of late years that total has been greatly reduced.

FRUITS.--The insects that reduce our annual fruit crop attack every
portion of the tree and its product. The woolly aphis attacks the roots
of the fruit tree, the trunk and limbs are preyed upon by millions of
scale insects and borers, the leaves are devastated by the all-devouring
leaf worms, canker worms and tent caterpillars, while the fruit itself
is attacked by the codling moth, curculio and apple maggot. To destroy
fruit is to take money out of the farmer's pocket, and to attack and
injure the tree is like undermining his house itself. By an annual
expenditure of about $8,250,000 in cash for spraying apple trees, the
destructiveness of the codling moth and curculio have been greatly
reduced, but that money is itself a cash loss. Add to this the
$12,000,000 of actual shrinkage in the apple crop, and the total annual
loss to our apple-growers due to the codling moth and curculio is about
$20,000,000. In the high price of apples, a part of this loss falls upon
the consumer.

In 1889 Professor Forbes calculated that the annual loss to the
fruit-growers of Illinois from insect ravages was $2,375,000. In 1892,
insects caused to Nebraska apple-growers a loss computed at $2,000,000
and, in 1897, New York f