16 BULLETIlSr 807, U. S. DEPARTMENT OF AGRICULTURE. 



destroyed. The experiments were carried on mostly in the fall, 

 shortly after all the adults had formed. Other experiments during 

 the spring, toward the end of the life of most of the weevils, gave a 

 complete killing with a lower degree of heat and a shorter time. 



Treatment of from 125° to 145° F. for several hours, as recommended 

 for bean and pea weevils in a recent Farmers' Bulletin (7), was not 

 tried. Experiments indicated, however, that the horse-bean weevil 

 is more difficult to kill than the ordinary bean weevil. Unless the 

 heat can be easily controlled and not allowed to go much above 145°, 

 other remedies will be much safer to use. 



FUMIGATION. 



Sulphur was first tried, using varying strengths up to 2 pounds 

 to 100 cubic feet of space for a period of 3 hours, and proved un- 

 successful. 



The standard remedy for bean weevils, carbon disulphid, was 

 next tried. The experiments were arranged to compare the effect 

 of infested beans fumigated while the insects were in the immature 

 stages and after all had reached the adult stage. Examination of 

 beans during the experiment gave the following results : 



Table XII. — Develop^nent of Brirrhns rufimnnus Aug. 15 and 17, 1918, at Al- 



haiiibra, Calif. 



Per cent. 



One-half to three-fourths "grown larvje 37. 6 



Full grown larvse : ' 20.9 



Total larvae , 58. 5 



Pupfe 20. 



Adults 21. 5 



.Table XIII. — Effect of carbon disulphid on the hroad-iean weevil. 





Percentage of beans with a] 1 we 



evils dead. 









Pounds CS 2 per 1,000 cubic feet. 



Exposed 18 hours. 



Exposed 24 hours. 





Treated 



in 

 August. 



Treated 



in 

 October. 



Treated 



in 

 August. 



Treated 



in 

 October. 



Check, not treated 





43 

 55 

 55 

 69 

 70 

 GO 

 74 



14 



43 

 52 

 62 

 60 

 82 

 62 

 79 



14 



2 





3 







4 



83 

 94 

 90 



100 

 99 



100 



81 



6 >. 



90 



6 



99 



7 



100 



8 . . 



100 



9, 10, 12, 15, 20 1 





100 









Conclusions from the carbon disulphid fumigation experiments: 

 1. Exposure in October when the insects were in the adult stage 



gave a 20 per cent better result than in August, when they were in 



the larval stage. 



