THE PRINCIPAL CACTUS INSECTS OF THE UNITED STATES. 



INTRODUCTION. 



The cactus plants of the genus Opuntia arc among the most strik- 

 ing objects to be seen in semiarid and arid regions. These plants, 

 which are extremely picturesque, are accorded a prominent place in 

 the illustrations and literature of early surveys, undertaken by the 

 War Department. 1 and, from a scientific standpoint, are of great 

 interest because they have been found to have adapted themselves to 

 existence in regions of small rainfall in many remarkable ways. The 

 numerous insects associated with cactus plants are naturally of great 

 interest. These insects have adjusted themselves to the general condi- 

 tions in the regions in which the plants grow T and have also adapted 

 themselves to the structure and habits of the plants themselves. 

 Moreover, cactus insects have ahvays held special interest on account 

 of the cochineal insect. The cultivation of this species, which is 

 indigenous to America, caused the prickly pear to be transported to 

 remote parts of the globe, where it has been planted for the purpose 

 of furnishing food for the dye-producing insect. The industry of 

 rearing the cochineal insect w T as for years a very important one. It 

 furnished valuable dyes which are still utilized for special purposes. 

 In the Canary Islands alone, in 1876, the exportation of cochineal 

 amounted to over 5,000,000 pounds. It has been determined that the 

 bodies of about 70,000 cochineal insects are required to make a pound 

 of the dried product. This gives an indication of the extent of the 

 industry in the Canary Islands, which did not, however, produce 

 nearly all of the supply which entered into commerce. 



Except for the cochineal insect, the species feeding upon Opuntia 

 have been until recently rather of scientific than of practical im- 

 portance. In the early days, since it was necessary to cultivate the 

 Opuntia plant as food for the cochineal insect, any species which 

 injured the plant w r ere of economic importance. In fact, the treatises 

 on the cultivation of the cochineal contain directions about the control 

 of various species which damaged the plant. With the decadence of 

 the cochineal industry, the cactus plants became nuisances, except 



1 Pacific Railways Report, vol. 4, p. 37, 1856; U. S. and Mexican Boundary Survey, 

 vol. 2, p. 35, 1859. 



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