Bui. 51, Bureau of Entomology, U. S. Dept. of Agriculture 



Plate XXI. 



Field and Laboratory Experiments with Insecticides. 



Fig. 86, Cage work in testing insecticides with weevils in field; fig. 87, experimental apparatus 

 for testing effect of hydrocyanic acid gas upon weevil stages exposed and in squares: fig. 88. 

 experimental apparatus used in determining effect of formaldehyde vapor upon weevil stages 

 exposed and in squares (original). 



