REPORT OF STATE ENTOMOLOGIST, 1898 221 
HINTS ABOUT INSECTICIDES 
A knowledge of the life history and habits of most of our insects is at 
present limited to comparatively few species and the number of well- 
known forms will probably ever remain relatively small. In spite of this 
drawback, destructive insects must be controlled or crops will be ruined. 
In many cases very precious time is wasted if the owner of a field must 
submit examples of the depredator to an expert at the experiment station 
or elsewhere, in order to ascertain the proper remedy. While establish- 
ing the identity of an insect is extremely important, the farmer, whose corn 
is being devoured at the rate of an acre a day by the army worm, is more 
concerned to know the best methods of fighting the pest than to learn its 
scientific name. Though the injuries by insects are not always so strik- 
ing as in the case of the army worm, the great advantage in controlling 
them at the inception of the attack can not be overestimated. It is a 
well-known fact that many insects succumb more readily to insecticides 
when young than later. ‘This is not only true of scale insects, but applies 
to certain caterpillars and other forms. ‘Though insecticides and their 
action have frequently been explained, the facts show, most conclusively 
great need of instruction in their use. 
How insects feed. Before attempting to control an insect, we must 
first ascertain how it can be affected. The large amounts of paris green 
and similar substances used, at once suggest the idea of poisoning its 
food. But can the insect under consideration be killed in that manner ? 
As paris green is effective only when taken internally, and is practically 
insoluble in water, it must be eaten with the food before the depredator 
can be killed. In other words paris green and similar poisons can be 
employed successfully against those insects only which bite off and 
swallow their food, and even then it is limited to cases where the poison 
can be applied to parts eaten. It is not enough to ascertain merely that 
the pest is one that devours, but the portion of the plant consumed must 
be known and the application made where it will be eaten. In the case 
of the apple-tree tent caterpillar, which devours the entire leaf, it makes 
little difference whether the poison be applied to the upper or under 
surface of the foliage, except that when on the latter it is less likely to 
be washed off by rains. It is a very important matter in the case of the 
elm-leaf beetle, whose larvae feed only on the under side of the leaves, 
rarely rupturing the upper epidermis, and for this reason poison applied 
to the upper side of the leaf would have little or no effect on them. 
Other biting insects are found in places where it is practically impossible 
to poison their food. Such are the leaf miners, tiny larvae that obtain all 
