12 PRINCIPAL CACTUS INSECTS OF UNITED STATES. 



of Entomology at Washington. This material was placed in the 

 hands of Mr. E. S. G. Titus and Mr. F. D. Couden. In spite of the 

 difficulties of rearing the specimens, due to the transportation to 

 Washington and the utterly different climatic conditions, these ento- 

 mologists succeeded in rearing a large number of specimens. This 

 material, with the rearing notes and the field notes supplied by 

 Mr. Griffiths, has been used in the preparation of this bulletin. 



In 1D07 Mr. Griffiths' field observations mgre than verified his 

 previous impressions regarding the importance of cactus insects. 

 By this time it had also become evident that the rearing work could 

 be carried on to much better advantage in the regions where the 

 Opuntia was grown and that field experiments in control were neces- 

 sary. For these reasons, in 1907 the investigation was turned over 

 to the branch of Southern Field Crop Insect Investigations. In con- 

 nection with other work Mr. F. C. Pratt and Mr. J. D. Mitchell were 

 detailed to institute an investigation of cactus insects in Texas. Mr. 

 Pratt's work was continued with serious interruptions, due to his 

 ill health, from late in 1907 until the fall of 1910. During this time 

 he and Mr. Mitchell accumulated a very large amount of information 

 about the insects associated with the Opuntia plant and regarding 

 feasible means of control of the more injurious species. The origi- 

 nal intention was that a publication on this subject should be pre- 

 pared by Mr. Pratt. His ill health, which became acute about the 

 time that sufficient material had been gathered to form the basis of a 

 bulletin, and his death soon afterwards, prevented placing the matter 

 in form for publication. This part of the work has been done by 

 the senior author, who has also made some field observations, although 

 the great majority of such observations were made personally by Mr. 

 Pratt and Mr. Mitchell. 



NUMBER AND CLASSIFICATION OF CACTUS INSECTS. 



As the result of the work we have done and that of the previous 

 investigators who have been mentioned, 324 species of insects are 

 known to be associated with the cactus plant. These divide them- 

 selves naturally into five categories, as follows: Species injuring the 

 plant, 92; parasites of injurious species, 28; scavengers, 73; flower 

 visitors, 40; species only incidentally associated with the plant, 91. 



The injurious species affect different, parts of the plant. In fact, 

 no important part of the plant is immune from injury. Twelve 

 species are known to attack the roots or stem. Twenty-seven species 

 attack the joints, of which 11 species feed inside of the joints 

 while 16 destroy the outer portion. A considerable number are 

 found in the blooms; a few of these are injurious, but others undoubt- 

 edly assist in the fertilization of the plant. The fruit is injured by 



13 species. 



