4-H CLUB INSECT MANUAL 57 
INSECTICIDES 
We get most of the insecticides that have been in use for a long time 
from metallic compounds or from plants. Those of metallic origin, 
such as lead arsenate, are inorganic insecticides; those from plants, 
such as nicotine from tobacco and pyrethrum from the pyrethrum 
flowers, are organic. Organic chemicals that are prepared in the 
laboratory (synthetic organic chemicals), such as paradichloroben- 
zene, are also used. Beginning with DDT, a number of new synthetic 
organic insecticides have been developed. These are made of ele- 
ments such as carbon, hydrogen, oxygen, and chlorine, combined in 
such a way as to form very complex chemical compounds. For ex- 
ample, the chemical name of DDT is dichloro diphenyl trichloro- 
ethane. The initials are the first letters of each part of the name. 
When insecticidal chemicals are first developed, they are not well 
standardized. The technical chemicals (commercial grade) should 
be used as insecticides only when they are properly prepared in formu- 
lations (mixtures) that can be used as dusts, sprays, or aerosols. 
Thus, we have five general types of DDT formulations: (1) Powders, 
to apply as a dust; (2) wettable powders, or powders that will mix 
easily with water, for spraying; (8) emulsion concentrates, to be di- 
luted (made weaker) by adding water and applied asa spray; (4) solu- 
tions, to be apphed without dilution; and (5) aerosols, to be apphed 
in the form of fine mist or smoke. Most other synthetic organic insec- 
ticides are prepared in similar formulations. 
Residual sprays, space sprays, and aerosols are new terms that have 
come into use since the new insecticides were developed. A residual 
spray is one that when placed upon walls and other surfaces leaves a 
residue (fine particles or crystals) that is effective for some time 
against insects that crawl or rest on the treated surfaces. Space sprays 
and aerosols are released into the air as a fog or mist. The minute in- 
secticide particles in the air come in contact with the insects and 
kill them. 
Some of the new insecticides can be applied in concentrated form 
and in very small amounts per acre. In fact, against certain forest 
insects, as little as 44 to 1 pound of DDT to 1 gallon of solution to the 
acre has been found to give good control. This has made airplane 
spraying practical, because there is no need for hauling a lot of excess 
liquid. 
Many of the old types of spraying and dusting equipment may be 
used for applying the new insecticides. However, new types of appli- 
cation equipment are being developed, such as mist blowers, fog gen- 
erators, and improved devices for dispersing insecticides from the 
air. 
The new synthetic organic insecticides are finding a useful place 
by expanding the range of effective and economical insect control. 
They will probably not completely replace the insecticides in use 
before DDT was developed. No material yet developed has been 
found effective for practical use against all insect pests. In fact, 
different formulations of a given material may vary in effectiveness 
against the same insect species. Years of testing under many different 
conditions are usually necessary to determine the value of each mate- 
rial and formulations of it against different kinds of insects. The 
