28 



lice obtained at this time were found chiefly among the husks of 

 nubbins and in crannies between the ensheathmg part of the leaves. 

 They were evidently restless, and the warmth of the sun at midday 

 aroused some of them to endeavors to find better quarters. These 

 were found wandering about the stalks. An almost microscopic ex- 

 amination of stalks which had supported thousands of aphides was 

 made after the lice disappeared without finding an egg. The root 

 form of the corn louse has not to my certain knowledge been ob- 

 served later than October 8. Its period has probably passed and 

 its purpose been served when the warm weather of July comes on, 

 and with it the aerial form. But to make sure as to whether or 

 not this form was hibernating in the ground, the roots of weeds, 

 grasses and corn in cornhelds were searched in November, but with- 

 out finding them. In the same fields at this time, the hibernating 

 viviparous females of Schizoneura j^anlcola were abundant on the 

 roots of blue grass and timothy. 



From these observations, it seems to me evidently either that (a) 

 Aphis maidis matures its egg-laying brood locally ; (b) that this brood 

 matures on some plant other than corn, or (c) that the brood appears 

 at intervals greater than one year, the species being in the mean- 

 time maintained by hibernating viviparous individuals. 



(a) The area over which the foregoing observations were made 

 will doubtless be quite uniformly infested early the coming spring 

 with corn plant lice. That these lice can have been so distributed 

 over so extensive an area, and at so early a date after hatching 

 from the eggs of locally developed oviparous females, can not be 

 believed. 



(b) If eggs Avere produced on some plant other than corn, it must 

 have been by plant lice born of the viviparous females which de- 

 serted the corn. The development of such a brood would have been 

 possible even after the hrst of November ; for Aphis mali matured 

 its oviparous brood on the apple trees after this date. When the 

 winged viviparous females of the corn louse began to mature rapidly 

 and scatter through the fields in the fall, close watch was kept of 

 available plants to see whether or not the lice resorted to them for 

 this purpose. Volunteer corn, which grew up along railroads late 

 in the season, became almost invariably stocked by these migrating 

 individuals, but on no other plant could the adults and young be 

 found. Wheat, oats and the perennial grasses seemed to be the 

 most likely to be resorted to, and the roots and stalks were 

 thoroughly examined. The lice peculiar to these plants were often 

 found in very great numbers, but in not a single instance was any- 

 thing found established on them which could be taken for Aphis 

 maidis. 



(c) The hypothesis that the lice hibernated as alate viviparous 

 females was the only one, then, left to me, and though not thoroughly 

 satisfied with the nature of the evidence, I am disposed to believe 

 that this is the usual manner of passing the cold months, and that 

 the oviparous brood appears only under specially favorable circum- 

 stances, perhaps locally. This conclusion is held subject to revision. 

 It is what seems most probable with the results of two seasons ob- 

 servation before me. 



