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 porti.on 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 hkely 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 



