THE BROAD-BEAN WEEVIL. 17 



2. A 24-hoiir exposure gave only about '2 per cent better resuUs 

 than one of 18 hours. 



3. A 48-hour exposure gave about a 5 per cent better result than 

 one of 24 hours. 



4. Seven pounds to 1,000 cubic feet for 24 hours was the least 

 amount to give a 100 per cent killing. 



5. Germination is not affected by the treatment, as beans treated 

 with 15 and 20 pounds per 1,000 feet for 24 hours gave 95 and 97 per 

 cent germination. 



Contrary to expectations, it was found that fumigating while the 

 insects were in the larval stage was less effective than in the adult 

 stage. A glance at Table XII will show that when the first fumiga- 

 tion took place in August, almost 40 per cent of the larvae were not 

 full grown. These were still eating within the bean, and had not 

 come up to the epidermis and formed the " window " through which 

 the adult emerges. It is evident, therefore, that the gas can not pene- 

 trate into the interior of the beans to the partially grown larvae as 

 easily as it can reach the full-grown larvae, pupse, or adults directly 

 under the skin. 



It was further observed that in the beans fumigated in August a 

 number of full-gTOwn larvae and pupae had been killed. 



Lengthening the time of exposure did not greatly increase the 

 percentage killed. This conforms to the opinions of Dr. TV. E. 

 Hinds (6) of the Alabama Experiment Station, who says, "As a 

 matter of fact, most, if not all, of the killing will have occurred 

 during the first 6 hours of the exposure, and the building may be 

 ventilated after that time, as a minimum, has elapsed, although it is 

 better to wait 12 hours or longer." On the effect of carbon disul- 

 phid on the germination of the seeds, Dr. Hinds states : " It would 

 appear from numerous tests that there is practically no danger of 

 injuring germination in treating seeds that are well matured and 

 dried out before treatment is given. li would not he wise to treat 

 moist seeds, or planting seed of any kind, during periods of very 

 humid atmosphere, as the seeds might take up enough moisture to 

 make them liable to injury from the vapor." 



HOLDING OVER SEED. 



Life-hist€ry studies showed that the horse-bean weevil had but 

 one generation a year, that it did not breed in the dry beans, and 

 that the last few remaining live adults died by the 1st of Jul3\ 

 By merely holding the beans over, therefore, until the second year^ 

 they will be uninfestecl as far as live weevils are concerned. The 

 beans should be stored in sacks or containers tight enough to pre- 

 vent any live weevils getting out during the first season. 



