66 



THE REPORT OF THE 



No. 19 



culture, to which crop it has come to be a veritable pest. Somewhere in the great corn fields 

 of Illinois and perhaps Iowa, this insect acquired the habit of breeding in the roots of corn, 

 and what seems to be a corn feeding race has sprung up and has slowly made its way eastward, 

 having now reached the eastern half of Ohio. As illustrating this feature of its diffusion, while 

 I have been closely watching its progress in western Ohio, I was unable for ten years to find a 

 single individual about Wooster, situated about 65 miles from the eastern line of the State, and 

 about 35 miles from Lake Erie. In the summer of 1900, however, I found a single individual in 

 my garden on the common sunflower, and, judging from past experience in other Stites as well 

 as in western Ohio, we shall soon have the insect in abundance.* Elsewhere^'' I have discussed 



Map 3. — The dotted area shows the territory over which Lercina accius, the Clouded Skipper 

 Butterfly, occurs. This is the area covered by the northern trend of southorn 

 species, ( Adapted from Scudder. ) 



the diffusion of the genus at considerable length, and it is unnecessary to repeat here what was 

 there stated, except to again call attention to the fact that our D. oittata has a very close relative 

 in D. trivittata on the Pacific coast and that our D. 12-pnnctata has an equally near relative in 

 the D. soror, also of the Pacific coast, while each has an intermediate species that seems to con- 

 nect the two in each case. 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 western slope and the 

 other the eastern. Prof. Cockereirs D. v'lttata var., incerta 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. tricincta, which occupies a similar relation to D. 12-punctata andl>. soror, 

 the evolution has advanced further and we have what we term a good species. From some more 

 recent studies of Mijochrons denticoUis and allied species of that genus, it would seem that some- 

 thing bimilar might have taken place with reference to that species as wellt. 



The southern terminus of the Appalachian system has a similar effect in dividing the streams 

 of insect migration, after such have passed to the eastward along the gulf coast, one branch 

 keeping along the Atlantic coast and the other to the west of the mountains, but without any 

 such influences on the species as seemingly occurs in Central America and Mexico. Thus, there 



*Jour. N. Y. Ent. Soc, Vol. HI, pp. 158-166 ; Vol. IV, p. 67. 

 fLoc. Cit., Vol. IX, p. 127. 



