28 
THE COLORADO EXPERIMENT STATION 
PART II. 
INSECTICIDES. 
THEIR PREPARATION AND USE. 
In order to be able to apply insecticides intelligently and with 
success, it is important to understand something of the habits of the 
particular insects to be destroyed and also of the nature of the rem¬ 
edies to be used. Many insects, like grasshoppers and the potato 
beetle, devour the surface tissue of plants, while others, like plant- 
lice, squash-bugs, and scale insects insert sharp tubular beaks into 
the tissues of plants and suck the sap from beneath the surface. 
Insects of the first class may nearly always be destroyed by means 
of food-poisons, such as arsenic, Paris green, hellebore, etc., while 
those of the latter class are unaffected by food poisons and have to 
be killed by substances that come in contact with the surface of 
their bodies, or in some other manner. It is not necessary to be a 
skilled entomologist in order to determine which class of insects 
is doing injury to the plants in question. If the leaves are ragged or 
eaten full of holes, it is practically certain that the injury is being 
done by an insect with biting-mouth parts. If the leaves simply 
wilt and dry up without having the tissue eaten away, the insect 
doing the injury is of the second type mentioned. The most com¬ 
mon remedies for this class of insects are kerosene emulsion, 
whale-oil soap, crude petroleum, and lime salt and sulfur washes. 
In many cases it is impossible to get an insecticide upon the 
insect that it is desired to kill, or upon its food, and then other 
means have to be used to prevent the injuries. Borers, under¬ 
ground feeders upon roots, and weevils living in seeds, are examples 
of such insects. 
In the pages that follow I shall not attempt to treat of all the 
methods used to destroy insects or avoid their injuries, but the 
more important ones only. 
SUBSTANCES THAT KILL BY BEING EATEN. 
■m 
Nearly all the food-poisons have for their active principle 
arsenious acid, or white arsenic (As s 0 3 ). White hellebore and 
borax, are about the only exceptions. 
1. WHITE ARSENIC. 
While this is the cheapest of the arsenical poisons, it is used 
but little, except for the purpose of making arsenical compounds 
