6 U.S. NATIONAL MUSEUM BULLETEST 25 6 



Costa. Each species usually possesses several hosts but shows a definite 

 range of limitation in the choice of its food plants. In addition to this 

 restriction, one finds a considerable variation in the degree of success 

 with which Dactylopuis attacks its range of hosts ; it may increase freely 

 and cause much damage to one species of Opuntia, yet multiply slowly 

 and have little appreciable effect on another Opuntia seemingly closely 

 related to the favored food plant. 



The cactus-feeding insects and mites are classified in the list on 

 pages 9-12, their predators and parasites are shown on pages 12-14, 

 and the cacti they attack on pages 15-28. The classification does not in- 

 clude the scavenging flies of the families Syrphidae and Stratiomyidae 

 nor the Argentine lycaenid butterfly Thecla melanis Drury, the larvae 

 of which probably feed on other plants as well as Cactaceae. The 

 capsid Hesperolabops picta Hunter, Pratt & Mitchell is included, since it 

 is mainly a cactus feeder, although it is reported to have other hosts. 

 Among the Phycitidae are included various forms known in the larval 

 stage only, and the same is true of one chrysomelid. 



The list makes no pretensions of being complete. For example, in 

 the Curculionidae, various species of Gerstaeckeria Champion recorded 

 by other authorities as cactus insects have not been added. 



When considering the variety of cactus insects, one is immediately 

 conscious of the omission of certain groups. There is only a single 

 record of one representative of the great Lepidopterous family Noc- 

 tuidae as a cactus feeder. Again, among the Heteroptera the large 

 family Pentatomidae is not represented, although the succulent growth 

 of prickly pear and other cacti should be particularly attractive to 

 these plant-sucking groups. 



Obviously there are dominant groups among the cactus insects, 

 which would mean that the cactus fauna have developed mainly along 

 certain lines. The most important group is found among the Phycitidae, 

 with about 40 species divided among a number of closely related 

 genera, all of which are restricted to cactus insects. Insects in these 

 genera occur in all cactus areas of importance, except Central America 

 where further investigations would probably reveal their presence, 

 and they have been found from the northern limits of the cactus region 

 in North America to the southern limits in Argentina and Chile. The 

 Phycitidae are internal feeders within the main stems, cladodes, and 

 fruit. 



The groups next in importance are the cerambycid genus Moneilema 

 Say and the curculionid genus Gerstaeckeria Champion, the former with 

 about 24 species and the latter with at least 10 species. Species of 

 Moneilema are found from Colorado in the United States to southern 

 Mexico, while Gerstaeckeria weevils occur in the United States, Mexico, 



