SPECIES ATTACKING JOINTS EXTERNALLY. 19 



Second instar. — Length, 4 rum. Very little change from first instar except 

 that the femora and prothorax have a slightly lighter color. Second joint of 

 antenna with almost straight sides. Spines on first and second joints more pro- 

 nounced. Length of stage, 4 days. 



Third instar. — Length, 5.5 mm. Spines on first and second antennal joints 

 slightly more pronounced, as is the raised callosity on the abdomen. The two 

 transverse brown slits very conspicuous. Prothorax changing to greenish. 

 Antennae inore distinctly flabellate; otherwise there is little change. Length of 

 stage, 4 days. 



Fourth instar. — Length, 6.5 mm. Greenish color on abdomen decidedly 

 darker; legs, antennae, head, and thoracic spines olivaceous black. No change 

 in spines. Length of stage, 12 days. 



Fifth instar. — Length, 7.5 mm. The abbreviated wing-pads appear and ex- 

 tend over the two anterior abdominal segments. General color dull olivaceous 

 black, except tips of antennae, which are orange. Prothorax considerably wider, 

 thus altering the appearance greatly, as the previous stages have a very narrow 

 prothorax in comparison to the abdomen. Length of stage, 14 days. 



The duration of the fourth and fifth instars was determined during 

 October; that of the earlier stages in July and August. Un- 

 doubtedly the duration of the last stages in summer does not greatly 

 exceed that of the earlier ones. 



DIMORPHISM. 



In the examination of several thousand of these bugs which have 

 been under observation- in the field and in rearing cages it was 

 noticed that there was a great variation in the color of the adults 

 from different localities. This variation is much more noticeable in 

 the nymphal stages. The color of the abdomen is either pea-green 

 or dark crimson. Repeatedly experiments in breeding these color va- 

 riations resulted in rearing adults which could not be distinguished. 



HIBERNATION. 



At a temperature from 45° to 50° F. these bugs appear to be rest- 

 less, congregating at times, and at other times dispersing in order 

 to find suitable quarters for hibernation. Throughout the winter 

 they are to be found in numbers under fallen cactus joints, in the 

 trash that accumulates at the base of the plants, under grass roots, 

 and in fact wherever they can obtain shelter in the immediate 

 vicinity of the Opuntia. They do not seem to travel any consider- 

 able distances from the plant upon which they were produced. 



Chelinidea tabulata Westwood 



The species Chelinidea tabulata Westwood has often been observed 

 in company with Chelinidea vittigera. It is not common, but if it 

 were it would easily rank as a pest of prime importance on Opuntia. 

 It is a Mexican species hitherto not known to occur in the United 

 States. In our collections it has been taken at many localities from 

 Austin, Tex., southward and westward. 



