42 
Colorado Experimkni Station 
PART II. 
INSECTICIDES 
THEIR PREPARATION AND USE 
There are two general classes of insecticides, those used against 
insects which have jaws and bite off and eat parts of the leaves, fruit 
or whatever they feed upon, and those used against sucking insects that 
have mouth parts in the form of a beak or slender tube through which 
they draw the juices of plants or the blood of animals. 
For biting insects, some form of an arsenical compound, such as 
Paris green or arsenate of lead is commonly used and the insects are 
killed by eating the poison. For the sucking insects, which take their 
food from inside the plants, some of the contact insecticides such as 
kerosene emulsion, lime and sulphur or tobacco, must be used. 
Contact sprays are often very effective in destroying the eggs of 
insects, especially those that winter over in the egg stage, as this will 
permit of spraying during the dormant season when a stronger solu¬ 
tion can be used without injury to the plants. 
Insecticides are generally used in one of three forms—liquid spray, 
powder, and fumes or vapor. 
SUBSTANCES THAT KILL BY BEING EATEN 
Arsenic in some of its compounds is the cheapest and most efficient 
poison used. As a very small amount of soluble arsenic is injurious to 
vegetation, only the insoluble compounds can be used. 
I. White Arsenic 
Pure white arsenic, arsenic trioxid (AS2O3), which comes in the 
form of a white powder, is the cheapest form in which arsenic can be 
obtained, but since in this form it is soluble in water, it cannot be used 
as an insecticide where it is applied directly to vegetation. 
2. Paris Green 
This is an arsenite of copper. It contains about 58% of arsenic 
(AS2O3). The National Insecticide Law requires that it contain a 
least 50% of arsenic trioxid. 
For many years this was a standard arsenical insecticide for or¬ 
chard use, but owing to the danger of injury to foliage, from some 
soluble arsenic present, it has been largely replaced by less soluble 
arsenical compounds. 
