No. 4.] INSECTICIDES. 363 



INSECTICIDES. 



BT A. H. KIRKLAND, ASSISTANT ENTOMOLOGIST, COMMITTEE ON GYPSY 

 MOTH, BIRDS AND INSECTS. 



Insect attacks of various kinds are chief among the causes 

 which hinder the successful development of crops, and, if 

 neglected, too often set at naught the labors of the farmer 

 or gardener. Thanks to the discoveries of modern science, 

 we are now able in nearly all cases to find a means of check- 

 ing these ravages by simple remedies if employed at the 

 right time. A brief digest of our present knowledge of 

 insecticides is given herewith, in the hope that, while it pre- 

 sents but little that is new, it may prove in some measure 

 helpful. 



The feeding habits of insects attacking the exterior parts 

 of plants afford us a ready means of separating them into 

 two general groups, — biting insects (various caterpillars, 

 beetles, etc.) and sucking insects (plant lice, scale insects, 

 etc.) . The members of the first group devour the substance 

 of the plant by means of their jaws, while those of the 

 second group secure their nourishment by the aid of a 

 slender beak inserted into the plant tissues. The substances 

 to be used in the destruction of insects are determined in 

 great measure by these feeding habits, and may in like man- 

 ner be separated into two classes : first, internal poisons 

 used against biting insects ; and second, external irritants or 

 contact insecticides employed in destroying insects of the 

 second group. The desirable qualities of an insecticide of 

 either class are : — 



