DISTRIBUTION OF THE OTHER GROUPS. 5 1 



In the lincata group it is evident that there are two chief centers of distri- 

 bution, one Central American and one North American, and that in each of 

 these a series of species has developed along lines independent of the others. 

 In the dilccta group there are also two distinct sets of species, one Central 

 American and one North American, both of which have followed the high- 

 lands and moved northward over the Mexican Plateau. In the hdldemani 

 group, however, the species, with the exception of L. dahlbomi, a few rare 

 species from the Pacific slope and lowlands of the Mexican area, and one 

 doubtful species from the north end of the mesa, all develop on the Central 

 American area. The lacerata group shows an advance eastward from the 

 center of origin into Yucatan, then northward along the Atlantic slope, 

 and finally up into the mesa from the eastern side, while the flavopustulata 

 group barely reaches the North American area. (See plates n, 12, and 13.) 



From the foregoing table may be drawn additional confirmation of the 

 correlation between species formation in the genus and natural physio- 

 graphic areas. What information we can derive from their geographical 

 distribution is strongly in favor of the view of a close correlation of species 

 development with topography and climate. 



The general cecological relations of each of the species in the Ii?ieata group 

 has been given, in as far as it is concerned in the distribution of the species. 

 In the other groups in the genus Leptinotarsa the same factors have the 

 controlling influence in the distribution of the various species and in the 

 determination of habitats. In some of the groups certain species are found 

 with a general distribution over a wide area of country. Most conspicuous 

 of these is L. dahlbomi (plate 13), which, of all the species in the genus, is 

 the least dependent upon a restricted habitat for its existence. In its wide 

 and varied range of distribution, from Guatemala and Yucatan northward 

 across the Rio Grande into Texas and New Mexico, it encounters a greater 

 variety of topographic and climatic conditions than any other species in the 

 genus and is one of the least variable. Others, as, for example, L. libatrix 

 violescetis, lacerata, icndedmlineata, and others, are restricted to a ven^ narrow 

 local habitat by similar environmental conditions. Some of the species in 

 this genus, L. rubiginosa, for example, are extremely limited in their dis- 

 tribution, owing to the rarity of their food plants and the conditions of 

 existence which they seem to demand. The main cecological factors which 

 control the distribution of all the groups of this genus are, first, moisture ; 

 second, temperature ; third, soil ; and fourth, altitude. 



