92 U.S. NATIONAL MUSEUM BULLETIN 25 6 



plants. They wander freely across the ground from one plant to an- 

 other; examples have been found 250 yards from the nearest prickly 

 pear. The eggs are deposited singly, and are affixed by a gummy 

 secretion on the surface of the segment, in cracks, at the union of 

 segments, or against the stem at, or just below, ground level. 



The larvae tunnel in the segments, stems, and branches, generally 

 in the basal parts. Their work is attended by considerable rotting of 

 the plant tissue; in fact they appear to thrive best in decaying seg- 

 ments. Branches of the large prickly pears often break off from the 

 effect of the activity of one larva at the junction of the main stems. 

 Two or three larvae in the base of a weighty tree pear may cause 

 the whole plant to collapse. In the case of Cylindropuntias the affected 

 stems tend to dry out rather quickly, and as a rule there is little wet 

 rotting of the branches and stems. The firm cocoons are constructed 

 of dead fibre within the attacked segments. 



No preference for specific host plants has been observed The vari- 

 ous species seem to attack all prickly pears and Cylindropuntias within 

 their range of distribution. Although Opuntia is the primary host, 

 other cacti may be included in the list of food plants. 



The forms that have been studied possess either one or two generations 

 each year, or one complete and a partial generation. With species 

 having an annual life cycle, the adults emerge in midsummer. Where 

 tv/o generations are completed or partially completed, there is usually 

 a larger emergence in the spring and a smaller emergence in the 

 autumn. The beetles may live for three to five months in the field, but 

 are capable of much greater longevity. Under conditions of close 

 confinement, females of M. ulkei have survived for a maximum period 

 of 300 days, while one male lived for the extreme period of 529 days. 

 The larvae may remain unpupated in the cocoons for several months. 



Most species are rather widely distributed, but a few appear to be 

 confined within limited areas. Certain forms, although found over a 

 wide range, have not been encountered in numbers; for example, 

 M. crassa in Texas, and M. appressa in New Mexico, Colorado, and 

 Utah. On the other hand, M. gigas in Arizona, M. laevigata in New 

 Mexico, M. ulkei in Texas, and M. variolare and M. rugosipennis in 

 Mexico are frequently very plentiful. A feature of the distribution, 

 which is probably associated with the wingless character of the adults, 

 is their prevalence in local areas. Thus, among the numerous fields of 

 Opuntia lindheimeri in the Uvalde district of Texas, M. ulkei could be 

 collected in quantity season after season from the same patches of 

 prickly pear, although it remained a rare insect in other 0. lindheimeri 

 infestations which appeared to offer conditions equally favorable to 

 its requirements. Similarly such species as M. gigas, M, laevigata, M. 



