10 PRINCIPAL CACTUS INSECTS OF UNITED STATES. 



where the tunas were utilized as food. 1 They occupied land that could 

 be used to advantage for valuable crops. In this way. in a few j^ears, 

 the plant was changed in character from a valuable one to a weed. 

 Incident to this change the insects feeding upon Opuntia assumed an 

 entirely different character. Instead of being considered pests, they 

 came to be looked upon as beneficial on account of their destruction 

 of the weed. In fact, in South Africa and Australia the encourage- 

 ment of the insect enemies of prickly pear has been proposed as a 

 feasible means of reducing the number of plants. 



Within very recent years, at least in so far as the United States is 

 concerned, there has been another revolution in regard to prickly 

 pear. It has been recognized for many years in the southwestern por- 

 tion of the United States that the plant furnished a supply of food 

 for cattle during drought that frequently prevented the starvation of 

 large herds. It was considered, however, that this was a rather poor 

 return for the loss of large grazing areas on which the plants grew 

 and which in normal seasons without the prickly pear would have 

 furnished large amounts of forage. Some years ago Mr. David 

 Griffiths, then of the Arizona Agricultural Experiment Station, 

 began an investigation of the feeding value of prickly pear. It Avas 

 soon found that the plant has a surprisingly high feeding value. 2 

 The greatest practical difficulty in the use of the plant for forage 

 was the spines, but it was found to be possible to eliminate this diffi- 

 culty by singeing the plants or by running them through machines 

 which chopped them into small pieces. It was also discovered by Mr. 

 Griffiths, 3 whose more recent work has been done as an agent of the 

 Bureau of Plant Industry of this department, that when prickly 

 pear is planted it responds readily to cultivation. In fact it was 

 found that artificial plantings of the pear with only meager cultiva- 

 tion furnished a growth in three years that was fully as great as the 

 growth under natural conditions in double that period. At this 

 point, however, it became evident that the insects affecting the prickly 

 pear would need to be taken into consideration. In fact it appeared 

 in the experimental plantings of the Bureau of Plant Industry that 

 the insect injury was one of the most important obstacles to the culti- 

 vation of the prickly pear as a farm crop. In this way there has been 



1 In this discussion we consider the prickly pear as a crop planted on a large scale 

 but do not overlook the fact that its fruit has been utilized as food for man from very 

 ancient times and is still an important human food in large areas. There has been no 

 revolution as regards the tuna as food for man. It has always been important. How- 

 ever, the tunas are obtained from wild plants, or from those cultivated on a compara- 

 tively small scale about houses, and thus represent a system of growth quite different 

 from the extensive field culture of the early days. 



2 The Prickly Pear and other Cacti as Food for Stock, by David Griffiths. (Bui. 74, 

 Bur. Plant Ind., U. S. Dept. Agr., March 8, 100",.) Feeding Prickly Pear to Stock in 

 Texas, by David Griffiths. (Bui. 01, Bur. Plant Ind., U. S. Dept. Agr., 1906.) 



3 Prickly Pear as a Farm Crop, by David Griffiths. (Bui. 124, Bur. Plant Ind., U. S. 

 Dept. Agr., February 19, 1908.) The Tuna as Food for Man, by David Griffiths and B. F. 

 Hare. (Bui. 116, Bur. Plant Ind., U. S. Dept. Agr., December 2, 1907.) 



