SPECIES ATTACKING JOINTS EXTERNALLY. 17 



It has been observed by Mr. J. D. Mitchell that the joints upon 

 which the bugs have fed, and which may not have shown any special 

 damage during the season, are the ones first injured by frosts during 

 the following winter. This indirect injury sometimes results in set- 

 ting the plants back by as much as the growth of two years. Another 

 form of injury which is suspected but not proven in the case of this 

 bug is the dissemination of the fungous disease Perisporium sp. This 

 disease causes large black spots on the joints. The infected area fre- 

 quently drops out, leaving a more or less circular opening through 

 the joint. The feeding habits of the bug are such as to render it very 

 likely to plant the spores of the fungus when it travels from one 

 joint to another. 



This species was first called to attention as an enemy of Opuntia 

 by Mr. F. W. Thurow, who, in March, 1893, reported to the Depart- 

 ment of Agriculture that. three species of Opuntia growing in Harris 

 County, Tex., were greatly damaged. 1 



DISTRIBUTION. 



This species is not confined to the prickly-pear region 'proper, 

 although there is no doubt that it greatly prefers that plant and 

 that it is much more abundant where the Opuntia occurs in large 

 numbers. Its western limit in Texas, so far as ascertained, is Brews- 

 ter County. In the east it occurs along the Gulf and inland as far as 

 Trinity County, Tex. It has been taken in Dallas and Parker 

 Counties, Tex., wherever Opuntia occurs. It has also been observed 

 in California, Utah, and Colorado, and in fact is generally distrib- 

 uted throughout the Western and Southern States. In the East it is 

 found in Louisiana, Alabama, and North Carolina and has been 

 recorded from Virginia. 



VARIATIONS. 



The following notes on variations in Chelinidea vittigera have 

 been furnished by Mr. O. Heidemann, who examined all of the 

 hemipterous insects taken on cactus: 



The species is exceedingly variable in structure of the body and in color. 

 The relative length of the head, described by Prof. Uhler as being two-thirds 

 the length of the thorax, can hnrdly be considered as a constant character. 

 There are specimens which have the head and thorax subequal in length or 

 equal. The peculiar prism-shaped antennal joints are more or less dilated, 

 in some examples very conspicuously. This variation in the dilatation of the 

 antennal joints is noticeable even in those specimens marked as reared from 

 Opuntia. The color of the antennae, elytra, and legs varies considerably, chang- 

 ing from reddish-brown into black. The darkest, most developed forms occur 

 in Colorado and Utah. 



1 Insect Life, vol. 5, p. 345. 

 50975°— Bull. 113—12 2 



