14 DISTRIBUTION AND DISPERSION OF I^EPTINOTARSA. 



THE DISTRIBUTION AND MIGRATIONS OF THE LINEATA GROUP. 

 Distribution and GEcology of the Species. 



LEPTINOTARSA UNDECIMLINEATA Stal. 



It is highly probable, although it can not be absolutely proven by actual 

 observation, that the Guatemala- Chiapas Plateau, when perhaps it had a 

 much lower altitude, was the original habitat, the center of origin, and first 

 center of dispersal for this group of beetles. That L. undecimlineata is the 

 most primitive of all the species in this group and close to the parent form 

 is reasonably certain. The data of its distribution, which has been given, 

 shows that, as far as is known, it is the only species of the group in Guate- 

 mala. It is evident that it did not come from South America, but is strictly 

 a Central American form. 



Of its habitat or habits in Guatemala I know nothing. In Chiapas, 

 Oaxaca, and Vera Cruz I have been able to study it in nature and to 

 discover some of the factors which control its range of distribution and 

 confine it to a restricted habitat. 



In a very general way the distribution is shown on plate i, where L. tmde- 

 cimlineata is shown to be distributed over the American Continent to the foot 

 of the great escarpment on the southern end of the Mexican region. It is 

 distinctly a tropical species. The distribution is irregular, it being confined 

 to the valley floors and the low coastal plains of Vera Cruz, Oaxaca, Tabasco, 

 and Chiapas, and southward, and it is not known from the Pacific coast regions. 



Throughout the entire area in which I have studied this species it is always 

 found in open grassland formations (plate 2), never in the forests, and is 

 local in its distribution, being limited to isolated colonies in narrow and 

 precise habitats, from which it does not wander far. These colonies are 

 maintained from year to year in almost exactly the same spot. The situa- 

 tion in which the colonies thrive best is where there is a growth of their food 

 plant upon the edge or within a few feet of the edge of a small, deeply-cut 

 stream, so deeply cut that the chances of overflow are slight, or on a slightly 

 elevated mound in the meadow or savanna, but there must be either an 

 abundant supply of telluric water or the superficial soil must be kept moist by 

 frequent precipitation. The soil most favorable to it is a fine residual or allu- 

 vial soil sufficiently free from clay and cementing materials, so that it does not 

 become too hard during dry times. These are the general conditions best 

 adapted to this insect — conditions which can be realized onl}^ in rather 

 restricted areas. The immediate edges of the rivers in the country in which 

 it lives are subject to extensive overflow, and hence are impossible sites, as 

 are also the open, level flood plains. Neither a hillside nor the talus slopes 

 at the foot of a hill provide the ideal conditions. In fact, only that portion 

 of the valley situated between the upper limits of the rainy season floods 

 and the talus slopes of the hillsides provides the conditions necessary for 



