8 BULLETIN 160, U. S. DEPARTMENT OF AGRICULTURE. 



The death rate in this experiment was very low, which is ac- 

 counted for to a certain degree by a decrease in the voracious ap- 

 petite of the beetles, which were encaged on a cabbage plant. Feed- 

 ing appeared to be more from the underside of the leaves, and usually 

 the epidermis was left intact. 



In the next experiment with potted plants spinach was substituted 

 for cabbage, since it seemed preferable to the beetles, particularly as 

 the cabbage plants had been growing for some time in the pots and 

 had become more or less stunted and tough. In this experiment fer- 

 rous arsenate was used at the rate of 1 pound to 40 gallons of water, 

 in which 40 pounds of cactus had been placed 72 hours previous. 

 Table IX shows results and mortality. The plant was sprayed April 

 2, and on April 4 five beetles were liberated on the plant and cov- 

 ered with a lantern globe. 



Table IX.- 



-Expcriment No. 18. — Cactus as an adhesive with ferrous arsenate. 

 Brownsville, Tex., 191.' t . 



Date. 



Beetles 

 present. 



Living. 



Dead. 



Feeding. 



5 







4 



5 







1 















4 



1 







3 



2 







2 



3 







Not feed- 

 ing. 



Apr. 4 1 5 



Apr. 5 1 5 



Apr. e 5 



Apr. 7 5 



Apr. 8 1 5 



Apr. 9 5 



The results here were much better than in experiments Xos. 16 and 

 17, and the beetles appeared to succumb more readily, since they fed 

 more rapidly. 



On April 6 a spray was made up of ferrous arsenate, using 1 pound 

 to 12 gallons of water in which 10 pounds of sliced cactus had been 

 placed 48 hours previous to spraying, insuring thorough glutinous 

 consistency in the spray mixture. Some spinach plants in pots were 

 sprayed previous to spraying plats in the field. On April 13. or one 

 week from date of spraying, six beetles were encaged on a plant and 

 observed for 10 days. Table X shows the nmnber of beetles that 

 succumbed. 



Table X. — Experiment Xo. 18. — Cactus as an adhesive with ferrous arsenate. 



Brownsville. Tex., 191J f . 



Date. 



> Beetles 

 present. 



Living. 



Feeding. 



Xot feed- 

 ing. 



Apr. 13 

 Apr. 14 

 Apr. 15 

 Apr. 16 

 Apr. 19 

 Apr. 20 

 Apr. 21 

 Apr. 23 



4 

 4 

 4 

 4 

 3 

 3 

 3 



