1 6 DISTRIBUTION AND DISPERSION OF LEPTINOTARSA. 



it is true, due to the processes of railroad building, but if the same condi- 

 tions had been produced by floods or other natural agencies which may act 

 rapidly to change local conditions by cutting new waterways, the newly 

 created possible habitats would in all probability have been seized upon with 

 equal suddenness. 



We see how definitely undecimlineata is limited in its distribution to a 

 particular portion of the locality in which it lives, and it is probable, there- 

 fore, that its present distribution through the valleys of Vera Cruz, Oaxaca, 

 Tabasco, and Chiapas has been a growth dependent upon the development 

 of appropriate habitats at successively higher and higher levels in the river 

 systems, so that the beetle has been brought by a series of steps nearer and 

 nearer to the Mexican region. Its food plant everywhere precedes it, and 

 as fast as appropriate conditions of soil and moisture are developed at any 

 place, the beetle occupies it. This process of reaching out for new sites is 

 easily seen on the eastern slopes of the Mexican highlands at Orizaba or 

 Jalapa, in the State of Vera Cruz, where well-established colonies are found. 

 From these colonies numerous individuals find their way to points higher 

 up on the valleys, where food, temperature, and moisture are favorable, 

 but where permanent colonies are not established, because the conditions of 

 existence at these points are unfavorable to aestivation and pupation ; and as 

 long as the conditions demanded are not fulfilled no permanent colony can 

 be established. It is not necessary that the soil should be of a special chem- 

 ical composition or temperature and rainfall of special amounts, but it is 

 essential that during pupation and aestivation the beetle shall not be sub- 

 jected to excessive desiccation or moisture, and that the soil shall be porous 

 enough to admit of an abundant supply of air. 



The southward distribution of this insect is not well known. The data is 

 meager, consisting of records of capture, and I have not been able to visit 

 these southern regions to study its habits and distribution there. However, 

 from the data which we have, it seems probable that it occupies the same 

 habitat there as elsewhere, and that it is limited by the same determining 

 factors as in the northern portion of its range. It has extended south to 

 the isthmuses of Panama and Darien. It is everywhere a Caribbean or Gulf 

 coast form, never, as far as our knowledge goes, occurring upon the Pacific 

 slopes. 



LEPTINOTARSA DIVERSA. 



The narrow range and the few observations that have been made upon this 

 species do not permit of any extended discussion of its distribution or the 

 control of its habitat. It is, as I have pointed out, a close ally of undecim- 

 lineata, and, like it, is confined to a narrow habitat. In the barrancas of the 

 Rio Grande de Santiago it occurs upon clumps of Solatium sp.?, which grow 

 near the edges of the cliffs and upon their faces and the steeper sides of the 



