16 



PRINCIPAL CACTUS INSECTS OF UNITED STATES. 



feeding generally gregariously on the joints of Opuntia and allied 

 genera. It is chiefly nocturnal in its habits. The first indications 

 of feeding are the occurrence of lighter circular spots on the joints. 

 The whitish excrement of the insect, which covers the surface of the 

 joint, is also conspicuous. During the winter the insects are to be 

 found in large numbers in a somewhat dormant condition under pros- 

 trate joints. 



This species and its congeners are restricted to cactus plants and 

 are by far the most important Opuntia insects occurring in the 

 United States. On account of the wide distribution and prolific 

 breeding of C. vittigera it is conspicuous in all localities where it 

 occurs. Within its range Mimorista favidissimalis Grote is proba- 

 bry more destructive to the plants, but that species is restricted to 



a comparatively small portion of 

 the area occupied by Opuntia. 



NATURE OF INJURY. 



The small circular discolora- 

 tions on the joints resulting from 

 the work of this insect do not 

 appear until feeding has pro- 

 gressed for some time. As soon 

 as they do make their appear- 

 ance, however, they are extremely 

 conspicuous. They may be found 

 upon only a few joints of a plant, 

 or where the bugs are more abun- 

 dant all the joints may be affected. 

 As the injury proceeds, the spots 

 become larger and coalesce, so that the whole area of the epidermis 

 assumes a deadened, yellowish, and pitted appearance. The whitish 

 excrement is discharged more profusely when the bugs are approached 

 and may possibly have some protective effect. 



As a result of attack the plant is weakened so that it soon falls 

 over. Where the bugs are numerous the fallen plants give somewhat 

 the same appearance as they would if battered down by heavy hail. 

 In some cases, where the attack is not strong, portions of the fallen 

 joints take root and give rise to new plants. More frequently, how- 

 ever, the joints are unable to recuperate and either dry up completely 

 or become the breeding places for the many species of scavenger 

 insects found associated with the cactus plant. 



As soon as the bugs, whether in the nymphal or adult stages, have 

 weakened a plant they migrate to other plants and continue the work 

 of destruction. 



Fig. 1. — A cactus insect, Chelinidea vit 

 tigera: Adult. Enlarged. (Original.) 



