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INSECTICIDES FROM A CHEMICAL STANDPOINT. 



By W. F. cooper, B.A. (Cantab.), F.C.S., 

 AND W. H. NUTTALL, F.I.C., F.C.S. 



{From the Cooper Laboratory for Economic Research, Watford.) 



As the title implies, this paper puts forward some ideas which, to 

 us, appear to lead to a wider range of choice in insecticidal substances, 

 and to possible improvements in their methods of application. 



We are chemists and make no claim to a special knowledge of 

 entomology; yet we have been concerned for some time with the 

 practical control of various horticultural pests and animal parasites, 

 and we venture to hope that the experience thus acquired may be of 

 some little value to the economic entomologist. 



On glancing down a list of the substances most generally used in the 

 preparation of insecticides, a chemist is at once struck by the surprisingly 

 small number of compounds which have been employed. It would 

 seem that until recently the changes have been rung on little more than 

 half-a-dozen materials : Bordeaux mixture — lime-and-sulphur — quassia 

 — arsenic — pyrethrum — paraflS.n, and so on. So-called improvements, 

 which are claimed from time to time, appear as a rule to be confined to 

 some slight modification of one or other of the existing formulae, the 

 number of which is already legion. 



In the past the attempts to control entomological pests have been 

 of too empirical a nature. Substances have been tried with little, if 

 any, regard to their precise mode of action, and when a moderately 

 satisfactory material has been found the experimenter has rested 

 content, where he might with profit have continued his enquiries along 

 those lines which this result should suggest. Empiricism generally 

 tends to stifle true research, and genuine progress rarely follows in its 

 train, while patient research on well-organised and systematic lines 

 almost inevitably paves the way to final success. 



It is not sufficient to discover that a certain compound is more or 

 less effective for the destruction of specific pests — the further step must 



