UNITED STATES DEPARTMENT OF AGRICULTURE 
DEPARTMENT BULLETIN No. 1160 
Washington, D. C. ▼ May 29, 1923 
STUDIES ON CONTACT INSECTICIDES. 
By Charles H. Richardsox, Insect Physiologist, Fruit Insect Investigations, Bureau 
of Entomology, and C. R. Smith, Chemist, Bureau of Chemistry. 1 
CONTENTS. 
Page. 
Nature of the study 1 
Procedure 2 
Detailed results of experiments 4 
Discussion of Table 1 7 
Toxic concentrations of selected compounds . 9 
Discussion of Table 2 9 
Toxicity of certain bases compared with their 
salts 10 
Page. 
Toxicity and volatility 10 
Toxicity and chemical structure 11 
General discussion 13 
Conclusions 13 
Literature cited 15 
NATURE OF THE STUDY. 
Contact insecticides are commonly understood to be substances 
which are capable of killing insects when dissolved or emulsified in 
liquid media or contained in dusts and brought into contact with 
their bodies. Fumigants, on the other hand, are substances which 
kill when applied in the gaseous condition. The distinctions are not 
sharp, as it is obvious that a volatile poison might kill by contact of 
the insect with either its liquid or its gaseous phase. 
This investigation involves a study of the toxicity of the more 
readily available organic compounds when used as contact insecti- 
cides. In addition, a number of compounds which offered possible 
value as insecticides or which served to indicate working theories of 
insect toxicology were made in the laboratory. It is expected that 
this investigation will form the basis for future study and possibly 
lead to the discovery of compounds of commercial importance. 
Most of the compounds tested showed little toxicity. These were 
ordinarily used in but few experiments unless questions of theoretical 
significance appeared to be involved. Those compounds which 
showed appreciable toxicity were subjected to greater study when 
available in sufficient quantity. Particular attention was given to 
the compounds which offered possible commercial value. 
In addition to the data on the insecticidal value of the various 
compounds, information on the effect of the various chemicals on 
1 The writers are indebted to W. S. Abbott, entomologist of the Federal Insecticide and Fungicide Board's 
laboratory at Vienna, Va., for assistance with some of the experiments. 
40421—23 
