THE PRACTCAL ENTOMOLOGST. 



101 



he recommended the farmer " to plow down im- 

 mediately the most infected portion of the field 

 with a deep subsoil plough," of course with the 

 idea of burying the larvae beyond any hope of re- 

 surrection. The advice was probably good, but to 

 be on the safe side, the whole field should have 

 been subsoiled. For just as likely as not, there 

 were full as many larvte on the uplands as on the 

 lowlands ; only iu the latter case they were exposed 

 to the eye, in the former case they were hidden 

 from view in their earth-colored cocoons. 



Mr. Rathvon seems to think it a strange thing 

 that the larva of the Wheat Midge should, as a 

 general rule, remain in the larva state, without 

 eating anything, from July to the following May. 

 But it should be recollected that for the greater 

 portion of this time it is enclosed in a cocoon, 

 which, although filmy and thin to the last degree, 

 is yet to all appearance impervious to water, and 

 must therefore check evaporation almost totally. 

 Besides, many other insects do precisely the same 

 thing. I have often haithe larva of the gigantic 

 Saw-fly of the elm ( Cimhex americana) spin up 

 early in July; yet as Dr. Harris observes, and as I 

 know from my own observation, the insect remains 

 in the larva state in its tough pod-like silken co- 

 coon all through the winter and until the following 

 spring, without the possibility of its obtaining any 

 food there. (Harris, liij. Ins., p. 519.) Hence Mr. 

 Rathvon's query, that " there may be some sub- 

 stance under the earth upon which the larva of the 

 Wheat Midge could feed during the long summer," 

 must be answered in the negative. Even if there 

 were some such substance, how could they 

 reach it,- when each is bottled up tightly in his co- 

 coon, and has to remain there until June in the 

 following year? 



THE NEW, OB COLOHADO POTATO BTTG. 



Since my last article on this insect was pub- 

 lished, 1 have collected a few additional facts re- 

 garding its geographical distribution, &e., which it 

 may be worth while to lay before the reader. 



Mr. T. T. Smith, of St. Paul, iMinnesota, noticed 

 it at that place in 1866. " They troubled the 

 Peach-blow Potatoes," he tells me, "very little, but 

 almost entirely stripped the leaves from the St. 

 Helenas." We had not previously heard of it in 

 this State. I had long ago showed that it had 

 passed from Nebraska into Iowa ; but how exten- 

 sively it prevailed in Nebraska, I have not been 

 able to ascertain. 



The Editor of the Wisconsin Farmer (April 13, 

 1867), finds that it was in Grant Co., Wise, which 

 lies in the extreme South West corner of the State, 

 as early as 1862, and that it was abundant on 

 the St. Croix river, which bounds the State on its 

 North Western border, in 1865. Mr. Townley, of 

 Marquette Co., Wise, which lies a little South of 

 the central part of the State, writes me word that 

 it existed in that neighborhood in comparatively 

 small numbers, in 1865, and swarmed there iu 

 1866. Already in 1865 he had heard that " there 

 was a bug, which, for two years at least, had been 



making havoc with the potato plant in the region 

 West of Marquette Co., and that it was considered 

 to be making its way thitherward." Hence we 

 may infer that this insect invaded Wisconsin some 

 two years before it invaded Illinois ; i. e., in 1862 

 instead of 1864 ; which is in accordance with the 

 general principle already laid down by me, namely 

 that the Southern columns of the Grand Army 

 have uniformly lagged behind the Northern co- 

 lumns, as they marched Eastward towards the sea. 



According to a letter from Mr. Byers, of Colo- 

 rado, which was recently published in the Wiscoic 

 siii Farmer, the Colorado Potato Bug is found only 

 in comparatively small numbers upon the Potato- 

 plant in that region. This is in accordance with 

 what, reasoning a priori upon general principles, 

 we should naturally anticipate. The Rocky Moun- 

 tain region, as I long ago demonstrated, is the na- 

 tive home of this insect; and as many species of 

 insects occur in that country which are not found 

 further East, it is not improbable that some can- 

 nibal or parasitic insect preys upon it there exten- 

 sively, which is not met with in the Valley of the 

 Mississippi. Wherever any animal has existed for 

 indefinite ages, there the Balance of Life has been 

 gradually adjusted, until by natural causes that 

 animal is controlled and kept within reasonable 

 limits. When this same animal suddenly migrates 

 into a new country, it is generally unaccompanied 

 by the species that had preyed upon it in its native 

 home ; and until the System of the Creation has 

 been slowly, and gradually modified, so as to origi- 

 nate a new Balance of Life — which process will pro- 

 bably occupy a very long time — it will often run riot 

 and sweep the whole country before it. We have 

 but to recur to the well known history of the Hes- 

 sian Fly, the Wheat Midge and the imported Ap- 

 ple-tree Bark-louse, to see how these principles 

 have already operated in the United States. 



To sum up all the known facts in a few words. 

 This Colorado insect now occupies more or less 

 completely Kansas, Nebraska, Iowa, Minnesota, 

 Wisconsin, Illinois and Missouri. I shall be greatly 

 deceived if we do not hear of it in Indiana, and 

 perhaps in Michigan, during the season of 1867. 



Mr. Tilden, of Davenport, Iowa, (the author of 

 the Tilden Tomato), says that he lost 30 acres of 

 potatoes in 1866 by this insect, and hardly feels 

 like going extensively into the business again. 

 {Prairie Farmer, April 6, 1867). Mr. Suel Fos- 

 ter, of Muscatine, in the same State, thinks that 

 they will have to give up growing potatoes iu that 

 region of country, and depend for their supplies of 

 that vegetable upon those districts which have not 

 as yet been invaded by the Bug. For himself, he 

 says that he does not propose to plant any potatoes 

 at all in 1867, except a few early ones, which he 

 intends to start in a hot-bed, and try to hurry for- 

 ward to harvest by the 4th of July. {Ibid, Jan. 

 26, 1867). 



The general result of all the evidence is pre- 

 cisely what I stated in the first instance, when for 

 the first time, in the first number of this Journal, 

 I laid open the Natural History of this insect. 



