138 ENTOMOLOGICAL NEWS. [May 



Mercer county, but leaving a central area to be occupied later by 

 the Flow but steady advance of the species now from all directions. 



The species had been reported from extreme southeastern Michi- 

 gan as early as 1889. the introduction being attributed to specimens 

 having probably been brought across Lake Erie by the winds from 

 some eastern locality. A year later a tew specimens were found at 

 Lansing, but it was not until 1892 that it began to make its pres 

 ence felt, and then only over a strip of country extending from 

 Monroe to' Grand Rapids. As the insect was abundant enoueh in 

 Paulding county, Ohio, to work serious injury to the clover crop in 

 1893, 1 am disposed to doubt the above mentioned theory of first in- 

 troduction into southeastern Michigan by way of Lake Erie and to 

 ascribe it to a continuation of the Ohio invasion. This seems all the 

 more probable, as it would be only after the insect had become seri- 

 ously injurious that information would be likely to reach me 

 through farmers, and the pioneers might be and probably were sev- 

 eral years in advance of this. A year later, in 1894, came the re- 

 ports from Mercer county, Ohio, which might have been due to the 

 southern dilfusion of the northern Ohio and southern Michigan in- 

 vasion, but the outbi'eak iu Dearborn county, Indiana, could not be 

 accounted iorin the same way, and this must, therefore, beattributed 

 to a separate introduction, for which there appears to be no other 

 explanation than that the species, like Phytonomus, was carried 

 down this river and left stranded in the lowlands in that section. 



Besides this, both correspondence and personal observation shows 

 that the species became noticeably numerous in eastern Ohio before 

 it did in the central portion of the State. It was not until 1896 that 

 it was observed on the Experiment Station grounds at TVooster, 

 which is slightly over 75 miles in a direct line from Columbus, and 

 slightly less 50 miles, also in a direct line, from Cleveland. 



The influence of rivers on the dilfusion of Diabrotica longicornis 

 is probably indirect, but, nevertheless, clearly defined. (See Map 2.) 

 In a previous paper presented before this body* I called attention 

 to the peculiar adaptation of this species in the cornfields of the 

 middle West, and there called attention also to the fact that it had 

 probably long ago made its way over ihe country, but was able to 

 retain its hold only in small and widely separated localities, until 

 the second tide of diffusion with the more highly developed food 

 habits of the larvae rendered its establishment in Ohio in its present 

 abundance possible. 



The trend of diffusion is now certainly parallel with the course 

 taken by rivers, though not necessarilv in the same direction as the 

 water flows. This insect cannot breed in great numbers in fields 

 that are subjected to a rotation of crops. Tiie same ground must be 

 devoted to maize for a series of years in order to enable the insect to 

 become even numerous, and it is the bottom lands that boixier the 



* Fifth Report Ohio Academy of Science, p. 41. 



