10 



BULLETIN 160, U. S. DEPARTMENT OF AGRICULTURE. 



It is apparent that although the application had been made for 

 more than a week, a sufficient amount of the arsenical remained to 

 have some effect on the feeding of the beetles. A later experi- 

 ment with iron arsenite showed the mortality of the beetles when 

 the} 7 feed on the plant immediately after spraying has been done. 



While spraying a plat of sugar beets at the South Texas Gardens 

 on April 15 the writer also sprayed some plants in the insectary, 

 using zinc arsenite in the powdered form. The cactus was used at 

 the rate of 1.8 pounds to the gallon of water and the zinc arsenite 

 at the rate of 1 pound to 64 gallons. The plants were sprayed on the 

 morning of the 15th, and on April 16 eleven beetles were liberated 

 inside the cage surrounding the plants. 



Table XIII. — Experiment No. 22. — Cactus as an adhesive with zinc arsenite, 



Brownsville, Tex., 19L' h 



Date 



Apr. 16 



Apr. 17 



Apr. 20 

 Apr. 21 

 Apr. 23 



Beetles 

 present. 



Living. 



Dead. 



Feeding. 



11 



11 







8 



11 



10 



1 



9 



11 



10 



1 



9 



11 



4 



7 



4 



11 



4 



7 



3 



11 



1 



10 







Not feed- 

 ing. 



This spray adhered and spread exceedingly well, although much 

 less cactus could have been used with equal results. However, no 

 precipitation was observed when the cactus was used at this strength. 



In experiment No. 23 a potted sugar beet was sprayed April 11 

 with zinc arsenite (powdered) at the rate of 1 pound to 35 gallons 

 of water, using three-fourths of a pound of cactus to each gallon of 

 water, the cactus having been placed in the water four days before. 

 Fermentation was prevented by the use of copper sulphate. On 

 April 15 ten belted cucumber beetles were encaged on the plant. 



Table XIV. — Experiment No. 23. — Cactus as an adhesive with zinc arsenite, 



Brownsville, Tex., 191/f. 



Date. 



Beetles 

 present. 



Living. 



Dead. 



Feeding. 



10 



10 







5 



10 



10 







5 



8 



2 



6 



2 



8 



1 



7 



1 



8 







8 







Not feed- 

 ing. 



Apr. 16 

 Apr. 17 

 Apr. 20 

 Apr. 21 

 Apr. 23 



It will be observed that in this experiment less than half the quan- 

 tity of cactus was used than was added in experiment No. 22, but 

 the zinc arsenite was increased to nearly twice the amount used in 

 the preceding experiment, and there was only a 10 per cent difference 



