INSECTS 



61 



47. Insecticides. 1 In our laboratory studies we have found that 

 there are two kinds of insects, namely those with biting mouth parts 

 and those with sucking mouth parts. Entirely different treatment 

 is necessary in dealing with insect pests of these two types. Insects 

 with biting mouth parts may usually be killed by thoroughly spray- 

 ing the parts of a plant upon which they feed with a mixture made 

 in the following proportions : 



Insects with sucking mouth parts, on the other hand, must be 

 treated with a spraying mixture which will actually touch their 

 bodies. Some of the " contact insecticides " for this purpose are 

 whale oil soap (one pound to five gallons of water), kerosene emul- 

 sion, and " black-leaf-40." The last named is preferable for killing 

 plant lice and it is mixed with soap as follows : 



1 The authors are indebted to Professor Glenn W. Herrick of 

 Cornell University for these formulas. 



