CHAPTER XIII 

 INSECTICIDES AND RELATED SUBSTANCES. 



A number of miscellaneous substances used in the agricultural 

 industries depend primarily upon their chemical composition for 

 effectiveness. Prominent among these substances are various 

 preparations for the control or suppression of parasitic pests 

 upon plants and animals and the restriction of contagious dis- 

 eases. Brief consideration will be given here to the composition 

 and action of the more important of these substances. For their 

 practical applications, reference should be made to special books 

 and bulletins on these subjects. 



The following classification of these substances will be followed 

 for the sake of order and convenience: 

 I. Insecticides. 

 II. Fungicides. 



III. Disinfectants, deodorants and antiseptics. 

 IV. Incidental materials. 



Insecticides are substances used for destruction of insects feed- 

 ing upon the fruit, foliage or bark of vegetation and for the re- 

 moval of ticks and similar pests from animals. These materials 

 have won general recognition as essential factors in the produc- 

 tion of high grade fruit. 



They may be classed as stomachic, contact, or gaseous poisons. 

 according to their mode of action. Such insects as the codling 

 moth of the apple and the "potato bug," which are surface feed- 

 ers, may be reached by poisons of the first class ; the aphides or 

 plant lice and other sucking insects must be attacked by poisons 

 of the second class; and the resistant scale insects and other 

 pests are most efficiently destroyed by fumigation with a poison- 

 ous gas. 



Stomachic poisons for insects are generally dependent upon 

 for their poisonous effects. Arsenic does not enter those 



