234 



The root louse hibernates as an egg in the earth, and, as far as known, 

 only in the nests of ants of a species identified for me by August Forel as 

 Lasius brtmneus, var. alienus. This ant is host and constant companion 

 of the root louse throughout the year. It is equally devoted, however, 

 to the common grass-root louse {Schizoneura corni, by Osborn's deter- 

 mination). The formicaries containing the corn louse eggs are most 

 frequently to be found in old hills of corn, late in autumn or in early 

 spriug, at a time when the ants are torpid within the earth, and when, 

 consequently, their miniug operations do not betray their presence. 

 They should be sought by digging or plov\ ing up the corn stubble in 

 the field, when, if auts be found, a thorough search of the burrows will 

 commonly show the aphis eggs, piled together in larger or smaller 

 quantities, the depth below the surface varying according to the sea- 

 son, and even the time of day. We have found them at a depth of 6 

 or 7 inches, and, again, scarcely more than half an inch below the 

 surface. In spring especially, when hatching tioie draws near, the ants 

 convey the eggs to the ui)per galleries of their nests during the heat of 

 the day (particularly if the weather be fine), but withdraw them for 

 the night and during cold wet days. 



The ants themselves pass the winter as adult workers, and as larvae in 

 various stages from the minute youug to those nearly full grown. The 

 time of hatching of the plant-louse eggs varies, of course, with the sea- 

 son, ranging, according to our observations, from the 10th to the 30th 

 of April. The commencement of the hatching season is fairly well in- 

 dicated by the opening of the radical leaves of the common smartweed 

 or heart weed {Polygonum persicarium) in the fields. The greater part of 

 the eggs are commonly hatched a week or ten days before corn planting 

 is fairly under way. 



The aphids of the first generation, that hatching from the eggs, are, 

 of course, wingless, oviparous females — the form commonly known as 

 the stem-mother, or, by Lichtensteiu's system, as the Pseudogyne fun- 

 datrix. This generation is readily distinguished by characters of form 

 and color from all that follow. Hatching commonly before the corn ap- 

 pears it is dependent at first in our region almost wholly upon young 

 plants of Polygonum. The roots of these are laid bare by the. burrows 

 of the ants, and upon these roots within their narrow tunnels the lice will 

 usually be found thickly clustered. Later, if tlie field be not planted 

 to corn, our common species of Setaria divides the attention of the lice, 

 offering, in fact, for a little time, a more succulent herbage than the 

 rapidly growing smartweed. 



The second generation begins to appear about the 10th of May, and, 

 by the 20th of that month may be itself mature. Many of this genera- 

 tion are winged, and others certainly wingless, as careful breeding ex- 

 periments upon isolated individuals have proven again and again. Our 

 earliest observation of the winged form of the root louse was dated May 

 13. This generation — the Pseudogyne emigrans of Lichtenstein — may 



