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



one of the most abundant of the many species to be found in the 

 lower Rio Grande Valley, is Opuntia lindheimeri Engelm., com- 

 monly known as the " prickly pear." This plant produces a fruit 

 that is available about one month in each year and one of which 

 the natives are especially fond. Further, the plants themselves 

 furnish food to many domestic animals and, it is* claimed, prevent 

 many cattle from dying during severe droughts because of their 

 highly watery composition. Many ranchmen protect their cacti 

 during a wet season and save them against the time of drought. A 

 gasoline torch, manufactured especially for the purpose, is used to 

 burn off the spines, and as soon as this burner is put into operation 

 cattle, recognizing the peculiar noise, come at once to obtain the 

 food thus rendered available. 



The prickly pear, besides being high in fluid content, is very 

 mucilaginous and is invariably used by Mexicans in the manufac- 

 ture of whitewash, to promote adhesiveness. The cactus is sliced the 

 evening previous to the application and placed in the water or in 

 the lime mixture, where it remains for several hours. The white- 

 wash is then ready for use. The utilization of cactus in whitewash 

 thus suggested to the writer its availability as a factor in promoting 

 adhesion in poisonous sprays. 



EXPERIMENTAL WORK WITH CACTUS. 



EXPERIMENTS WITH ZINC ARSENITE. 



On March 23, 1913, 20 pounds of cactus were sliced lengthwise and 

 immersed overnight in 50 gallons of water. The next morning 2 

 pounds of zinc arsenite in paste form were added, and after a thor- 

 ough mixing spraying was commenced on sugar beets which were 

 being injured by the belted cucumber beetle (Diahrotica balteata 

 Lee.). 1 



A previous experiment demonstrated that cactus yields a higher 

 percentage of mucilaginous matter if sliced at right angles to the 

 spines, and, moreover, the time required for preparation is materially 

 shortened by this method. It is best, however, to cut the larger pads 

 both ways, since, owing to the cellular structure of the pads, this 

 method insures a more copious and rapid flow of the juices. The 

 result obtained from the use of the spray, at the rate of 20 pounds 

 of prepared cactus to 50 gallons of water, was gratifying; the spray 

 not only adhered to the foliage better, but spread more uniformly 

 over the surface of the leaves. The quantity of cactus required to 



1 Accounts of this species, by Dr. F. H. Chittenden and Mr. H. O. Marsh, have been pub- 

 lished in Bulletin No. 82, Part VI, Bureau of Entomology, U. S. Departemnt of Agricul- 

 ture, pages 69-71 and 76-82, December 8, 1910. These include illustrations of the stages, 

 notes on life history, lists of food plants, and technical descriptions of the different 

 stages. 



