6 



BULLETIN 160, U. S. DEPARTMENT OF AGRICULTURE. 



The time required to kill all of the beetles placed on the' sprayed 

 plant was approximately six days, provided all specimens began 

 feeding immediately after being placed on the poisoned plant. 



In the next experiment 2-| pounds of arsenate of lead were used to 

 50 gallons of water. The host plant was spinach that had been grow- 

 ing in the pot for some time. The spraying was done during the 

 morning of April 14, and at 4 p. m. on the same date, after the poison 

 had dried, 10 belted cucumber beetles were placed inside the cage and 

 on the plant where possible. Table VI shows the mortality : 



Table VI.- 



-Eoeperiment No. 15. — Cactus as an adhesive with arsenate of lead, 

 Brownsville, Tex., .1913. 



Date. 



Beetles 

 present. 



Living. 



Dead. 



Feeding 



Not feed- 

 ing. 



Apr. 16 

 Apr. 17 

 Apr. 24 



The spray here used was not so effective as in experiment No. 14, 

 the mortality being only 80 per cent at the end of nine days. The 

 plant died from some cause about the 24th of April, and probably 

 very little feeding was done during the last few days the plant lived 

 after being sprayed. 



FURTHER EXPERIMENTS. 



The results obtained in the foregoing experiments had been so 

 favorable that further experiments on a larger scale were commenced. 

 Several thousand pounds of the prickly pear were used in the work, 

 and as the regular " pear burner," or torch, was employed to singe 

 the spines from the pads, they could now be handled with some com- 

 fort. The work has been conducted in a small way and on a large 

 scale with about the same degree of success. It requires only a short 

 time to burn the spines from enough cactus to make a sufficient 

 amount of adhesive material for several thousand gallons of spray 

 mixture. 



The list of insecticides that have been employed in combination 

 with cactus as an adhesive includes Paris green, lead chromate, zinc 

 arsenite (in both paste and powder forms), lead arsenate, ferrous 

 arsenate, and iron arsenite. The preceding pages give an account 

 of experiments with zinc arsenite in the paste form, Paris green, and 

 lead arsenate in the paste form, while the experiments that follow 

 will include zinc arsenite in the powder form, lead arsenate in paste 

 form, ferrous arsenate, and iron arsenite, the last two used in the 

 powder. The powdered zinc arsenite gave excellent results in every 

 instance when used in combination with cactus water, and the mor- 

 tality was in some cases higher than when three times the weight in 



