No. 5. DEPARTMENT OF AGRICULTURE. 381 



EEPORT ON INSECTICIDES 



By J. D. HERR, Lancaster, Pa. 



The term insecticides is used to designate that class of substances 

 which are known to react fatally upon insects. Of these substances, 

 standard works upon the subject treat upwards of 150 separate 

 chemical compounds and many times this number of formulae, not 

 including secret or proprietary preparations, as being useful in com- 

 bating injurious insects. There are no doubt others still which would 

 also be effective for this purpose, but the expense of using them on 

 any large scale would be prohibitive. A very small fraction of these 

 substances will be embraced in this report for the reason that my 

 time does not permit of even a brief mention of the relative merits 

 of a large number, neither is this necessary, for, as a matter of fact, 

 only a few are available for use in a commercial way, for, any 

 chemical substance to be utilized in the struggle against parasitic 

 insects ought to respond to the following different requirements: 

 (1) To destroy the parasite or arrest their evolution in the least 

 possible time. (2) To poison the parasite without at the same time 

 injuring the host plant and to preserve its properties for some time. 

 (3) To be cheap so that their use on a large scale will be economical 

 and profitable. 



Of the substances available there are less than a dozen possessing 

 these qualities, but by the use of these man is fairly well armed in 

 his combat with insects for the possession of the fruits of the 

 earth. Of these substances the following nine in number are used 

 in 98 per cent, of the operations directed against insects: (1) Paris 

 green; (2) Arsenate of lead; (3) Bordeaux-arsenates ; (4) Lime-sul- 

 phur solution; (5) Soap; (6) Emulsified oils; (7) Tobacco; (8) 

 Hydrocyanic acid gas; (9) Carbon bisulfide gas. It is but the truth 

 to state in this connection that there still are a number of insect 

 pests which the combined wisdom and ingenuity of the most learned 

 entomologists and chemists have as yet been unable to control. 



HOW INSECTICIDES ACT 



Insects are destroyed either by means of internal poisons applied 

 to the parts on which they feed so that the poison is ingested with 

 their food, or by materials which kill by their action on the external 

 surface of the insect. The nature and habits of each insect there- 

 fore determine the agent to be used in controlling it. Mandibulate 

 or biting insects are combated by the use of stomach poisons while 

 haustate or sucking insects are destroyed by caustic or gaseous sub- 

 stances. 



PARIS GREEN 



Pure Paris green is composed of copper oxide, acetic acide and 

 arsenious oxid, cliemically combined as aceto-arsenite. Commercial 

 grades often contain many impurities, but the National Insecticide 



