about iwo weeks old. Their young, in turn, reproduce in tiie same 

 way. one generation succeeding another at shorter intervals as the 

 weather warms up, until in midsummer they are only a week apart. 

 The average number of complete generations for the season is about 

 sixteen in the latitude of central Illinois. 



4. The second generation of this series begins to appear in cen- 

 tral Illinois about the first of May, and the oldest of these will begin 

 to give birth to the third generation on or before the middle of that 

 month. So rapid is the rate of reproduction that by the end of June 

 as many as six generations may have made their appearance. 



3. The root-lice of the first generation— those hatching from the 

 egg — are all wingless ; but beginning with the second generation a vari- 

 able percentage of this and of all following generations may ac(|uire 

 wings. These winged root-lice, called migrants, may thus begin to 

 appear early in May. 



f). By means of these winged insects originating in old corn 

 ground, fields not infested the year before may become infested from 

 the first week in May onward. Root-aphis injury is thus like a con- 

 tagious disease, spreading from field to field on the wings of the es- 

 caping migrants. .As these fall to the ground they are taken in charge 

 by the corn-field ant. which carries them under ground and places 

 them on the roots of plants, where they begin to feed and to bring 

 forth ]i\ ing young precisely as do the wingless ones. The young born 

 from winged mothers are wingless or winged, according to circum- 

 stances, just as are those whose mothers are themselves without wings. 



7. As the winged lice may ])egin to come up out of the ground 

 and fly away even before corn is planted for the new crop, and will 

 continue to do so thruout the season, fields that were not in corn 

 the vear before may become infested ])y these winged migrants and 

 their young while the corn is still very small. 



8. The corn-field ant is indispensable to the root-lice, which it 

 carries about from ]ilace to j^lace as may be necessarv, transferring 

 them to the roots of fresh plants when those they have been feeding 

 u])on become sapi^ed or overcrowded. 



0. Tf an old infested corn field is planted to some other crop than 

 corn, the root-lice living in it feed on the weeds until these are smoth- 

 ered out by the new crop-plants. Many of them then acquire wings 

 and fly away, and others are eaten by the ants which have them in 

 charge. The field is in this way virtually cleared of them; but the sur- 

 vivors are widely dispersed, to infest other fields. 



10. If an old infested corn field is planted to corn, the lice, placed 

 at first on the roots of the corn-field weeds, are transferred bv the 



