27 



marriage, but it is held that this could not be continued for any 

 great length of time without injury to the species, and eventually, 

 it is thought, would result in its extermination. There are certain 

 species of plant lice, however, of which no males or oviparous 

 females have been seen. Such species are thought to produce males 

 and egg laying females locally or only at seasons which from some 

 unknown cause are especially favorable to this method of reproduc- 

 tion. 



Observations made by the writer during the past season indicate 

 this habit for Ayhh viaidls. From the latter part of May when 

 this plant louse appeared on the corn till the middle of November 

 when the corn had long been dry and the ground had been many 

 times frozen, the corn louse was followed with special care ; and 

 though hundreds of individuals were dissected under the micros- 

 cope, only wingless and winged viviparous females were seen during 

 the season. About October 6th, most of the sorghum cane in Cen- 

 tral Illinois was ripe and ready for the mill. Aphis maidis had been 

 during the season abundant on the blades and to save itself must 

 now depart. Upon examination the species was found to be repre- 

 sented mostly by pupse and alate females. The pupse, as was found 

 by confining them, were rapidly maturing and the winged adults 

 were leaving the sorghum and scattering in all directions. While 

 standing at the edges of such fields at this time one's person inter- 

 rupted the flight of many of these winged lice. The roots were 

 now careifully searched for the root form, but it was not to be found 

 in places where at the beginning of the season it was common. 

 Whole plants were searched with the glass for eggs, and, though 

 some of them had afforded nourishment to hundred of aphides dur- 

 ing the summer, no eggs could be found. The lice which were thus 

 forced to leave the sorghum field doubtless resorted to the corn, 

 which was less advanced and for some time afterward continued to 

 furnish them appropriate food. 



With the advance of the season the lice upon corn were also de- 

 prived of food. But in this case the irregular development of the 

 stalks which prevailed in most fields served to collect the lice into 

 great colonies by driving them gradually from their stalks to the 

 greener and less matured ones. At the last most of the lice were 

 to be found between the outer husks of the greener ears and upon 

 dwarfed and immature stalks. These had not all collected there as 

 winged females, for the wingless louse showed itself capable of leav- 

 ing a stalk and finding a better one. Both wingless and winged 

 females of of the aerial form were now isolated and confined : both 

 were found to give birth to living young. On the ninth of Novem- 

 ber numerous specimens were collected in the fields and carried to 

 the house. Among them were many winged females, some pupae 

 and a few young. All proved to be viviparous. Some of them 

 were alive November fifteenth ; on the twentieth of this month the 

 last winged female died with its body distended with matured em- 

 bryos (11 were counted.) The last to succumb was a pupa which 

 died some days later. 



The specimens seen in the fields November 9th, were the last 

 ones observed alive out of doors. Previous to this date there had 

 been severe frosts, and the corn was nearly all dry and hard. The 



