MEXICAN BEAN BEETLE — WHITE 353 



of the insecticides available was best suited. A large number of 

 insecticides were tested in field plots of garden beans near Birming- 

 ham, Ala. From these first tests the better known arsenicals such 

 as lead arsenate and calcium arsenate were apparently satisfactory. 

 However, after a number of field experimjents had been performed 

 with lead arsenate, it was noticed that bean plants treated with this 

 material were sometimes stunted and were a darker green than nor- 

 mal. In one instance such severe injury followed its use by a grower 

 that a complete loss of crop resulted. This was an unlooked-for 

 development as lead arsenate had long been considered a standard 

 stomach poison for insects and one which could be tolerated by most 

 plants and had been used in the West to control the bean beetle. 

 Zinc arsenite had also been used for the control of the beetle in 

 the West, but its use caused injury to the bean crop in the South. 

 Apparently the atmospheric conditions in the South rendered the 

 foliage of the bean plant susceptible to the action of these arsenicals. 

 Paris green, while toxic to the bean beetle, was very injurious to 

 the plant foliage. 



The work with calcium arsenate is of particular interest because 

 it demonstrated the variability in different types or brands of this 

 chemical to bean foliage. Throughout the early tests with calcium 

 arsenate it was found that one particular brand was toxic to the 

 bean beetle and would not cause foliage injury when diluted with 

 hydrated lime, and as a result such a mixture was recommended 

 for bean-beetle control. Calcium arsenate, being cheap and readily 

 available, was extensively used. However, with the spread of the 

 bean bettle many different brands of this insecticide were used by 

 the grower, and complaints were received of chemical injury to the 

 bean crop. Studies indicated that some brands of calcium arsenate 

 were not suitable, and an extensive investigation was begun of the 

 effect of all available commercial brands of calcium arsenate on 

 the beans grown in the field. It was soon determined that the 

 brands varied greatly in their effect on the plant. It was also 

 learned that when the material was applied during periods of high 

 humidity, injury was more likely to follow than when the atmosphere 

 was dry. Chemical analyses made by chemists who were cooperating 

 in the work indicated that there was no appreciable difference in 

 the chemical composition of the various samples. 



It was discovered that a sample of calcium arsenate that normall} 

 seriously injured foliage, lost its injurious qualities when auto- 

 claved — that is, placed under steam pressure. Further investigation 

 also indicated that the heat treatment of calcium arsenate, while 

 it reduced the toxicity to bean foliage, also reduced tlie toxicity to 

 the insect. As a result of these investigations much research 

 relating to the manufacture and composition of calcium arsenate 



