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160 Journal New York Ent. Soc. [Voi. hi. 



the continent of North America. This species appears to prefer the 

 lower altitudes, as it has not been found above the 5,000-foot level, and 

 over the area of its greatest abundance in the Mississippi valley the ele- 

 vation is generally less than 2,000 feet, and in Illinois, Indiana and 

 Ohio it is less than 1,000 as a rule. I have previously shown that it 

 can breed freely in low and damp localities, and Mr. Harrington found 

 it in New Brunswick abundantly in the " dyked lands" known, as the 

 Big Tantramah Marsh. The rapidity with which this has increased in 

 numbers, in some portions of the country, during quite recent years, is 

 simply astonishing. Where I could scarcely get specimens enough for 

 a series in my collection, twenty years ago, it is now one of the most 

 injurious insects known to the farmer, and this, too, at an elevation of 

 not over 900 feet. Over the western third of Ohio, across Indi'ana and 

 Illinois to the Mississippi River, through Iowa, eastern Kansas and 

 eastern Nebraska, is largely a prairie country, and such a part of this 

 area as was in cultivation up to i860 was devoted mainly to wheat 

 growing. From about 1S65 onward farmers ceased to raise wheat as 

 a leading crop, and corn became king of the cereals. Sometime between 

 1865 and 1875 this species oi Diabrotica seems to have been attracted 

 to the immense corn fields by the inexhaustible supply of food they af- 

 forded for the adults, and as later investigations have shown, for the 

 larvae also, and these immense stretches of corn lands soon became 

 breeding grounds for vast myriads of the insect. So far as we now can 

 see, the centre or this outbreak, if such it might be called, was in cen- 

 tral or northern central Illinois, and it is here that appears to have 

 evolved a race not differing specifically or perceivably, yet whose larvae 

 develop on the roots of Indian corn, while the adults may subsist alike 

 on the silk and pollen of the corn, the bloom of Solidago, thistle and 

 clover, and the result has been that not only has the species increased 

 enormously in point of numbers and far above what could ordinarily 

 exist in the natural flora, but there seems to have been a sort of over- 

 flow of this race, precisely as though a slow but constantly moving wave 

 had spread out over the west, north and east; these directions being 

 governed by the area continually planted with corn. In Ohio this 

 problem offers a fine illustration of the effect of cultivated plants on the 

 spread of insects. The area over which the species occurs, even rarely 

 as my observations of the last four years have shown, is continually be- 

 ing extended to the eastward, it having been found abundantly this year 

 where the most careful search failed to reveal it last year or the year be- 

 fore last. In Ohio more or less of the inland streams flow more or less 



