1903] WEBSTER: — DIFFUSION OF INSECTS £^3 



What is now known as Phyoptera astur Cramer occurs in South America 

 north to Arizona and New Mexico. Heterocampa biundata occurs from Panama 

 through Guatemala and Mexico to Florida and New England. Macrocanpa 7?iar- 

 thesia is known from Brazil through Central America to Texas, Georgia, and Maine. 

 The two latter species do not occur on the Pacific slope. 



The genus Diabrotica, of the Chrysomelidae, offers some good illustrations 

 of the diffusion of species of Coleoptera from the far south to the north into 

 North America. There are in Columbia and Venezuela, about one hundred known 

 species of Diabrotica, of which eleven extend into Guatemala, eight into Mexico, 

 and one into the United States. Several of our most common species of this genus 

 can be traced directly to Central America, D. longicornis having been found in 

 Yucatan. In fact, with but a single exception all of our fifteen North American 

 species can be traced into Mexico, and some even farther. Only recently a 

 Mexican species, Diabrotica peregritia, has been found just over the Rio Grande 

 River, at Brownsville, Texas. Elsewhere (Journ. ent. soc. N. Y. vol. 3, p. 158-160 ; 

 vol. 4, p. 67) I have discussed the diffusion of the genus at considerable length, 

 and it is unnecessary to repeat here what was there stated, except to call attention 

 again to the fact that our D. viftata has a very close relative in D. trivittata on the 

 Pacific coast, and that our D. 12-piinctata has an equally near i^elative in D. soror, 

 also of the Pacific coast, while in each case there is an intermediate species that 

 seems to connect the two. This phenomenon I attribute to the fact that the 

 original stem species may have become separated far to the south, and one branch 

 followed the Pacific and the other the Atlantic Maritime trends, and Professor 

 Cockerell's D. vittata var. i/icet-fa, coming between the former and D. trivittata, 

 would seem to give us an illustration of an intermediate species in the process of 

 evolution, while in D. trici/icta, which occupies a similar relation to D. 12-punctata 

 and D. soror, the evolution has advanced further and we have what we term a 

 good species. From some more recent studies of Myoc/irous deuticoUis and allied 

 species of that genus, it would seem that something similar might have taken place 

 with reference to the northeastward trend of diffusion. Since mapping the distri- 

 bution of the genus Myochrous in the United States, in 1901,^ I have found that 

 M. squamosus occurs in Illinois and Kentucky, thus indicating that the latter, like 

 M. denticolUs, has swept broadly to the north and eastward. 



The common Dynastes tityus occurs from Brazil through Central America and 

 Mexico, and in the United States from Texas to Illinois and east to southern New 

 York and New England. The Cotton boll weevil, Anthonomus gra?idis, which is 

 spreading its devastating hosts through the cotton fields of Texas, was unknown on 



^ Journ. N. Y. ent. soc, 1901, vol. 9, p. 127-132, pi. g. 



