558 EXPERIMENT STATION RECORD. 



" Two distinct types of curl are manifested in this disease — the inward 

 and the outward, or retracted. . . . The disease can not be due to loss of plant 

 juices extracted by leafhoppers, but rather to the introduction by those 

 insects of an active agent. Few or no beets that develop curly-top symptoms 

 ever recover. Beets may fail to show symptoms of curly-top to the end 

 of the season if attacked by leafhoppers after they have attained consider- 

 able size and vigor. Yet the trouble is initiated and transmitted to the 

 root, only to develop with full virulence in the first shoots the following 

 spring if they be planted out for seed production. ... It is useless to malie 

 selections for seed from fields badly affected with curly-top. The inward typ«> 

 of curl is generally produced on young beets. The retracted type appears on 

 seed beets and on sugar beets that had attained considerable size and vigor 

 before the symptoms developed. Until recently curly-top symptoms had been 

 noted on no other plants than beets, but the writer noted the symptoms on 

 cabbage in 1909." 



" It is considered advisable to plant as early as practicable after danger of 

 late frosts is over, even to take some risks of late frost, in order to get the beet" 

 well established and vigorous before leafhoppers are likely to be numerous." 



A bibliography is appended. 



A new gall-making' psyllid on hackberry, T. D. A. Cockerell {Eiit. News, 

 21 {1910), Xo. -J, pp. ISO, ISl). — PuchiipaijUa rohweri, which forms galls on 

 the underside of leaves of Ccltis reticulata at Boulder, Colo., is described as 

 new. 



Papers on cereal and forage insects. Contributions to a knowledge of the 

 corn root-aphis, R. A. Vickery {U. >S'. Dcpt. Agr., Bur. Ent. Bui. So, pt. 6, pp. 

 Oil -118, pi. 1, figs. 6). — ^The results of recent studies of the corn root-aphis, 

 particularly in the Southern States, are presented in this paper. 



Experiments show that if the apterous females of Aphis maidirradicis are 

 transferred to the roots of corn or cotton fi*om several of their wild food 

 plants, or if they are transferred from corn to cotton, they will produce young 

 and establish colonies. In order to determine the preference of this louse 

 for cultivated food plants, seeds of a number of species were plauted near 

 infested corn rows, trusting to the ants to transfer the aphids from one 

 plant to another. When examined on June 5, muskmelon and watermelon 

 plants and sweet corn were found to be quite generally infested, while turnips, 

 cowpeas, beans, and radish had but few lice uix)n them. The ants found in 

 attendance wei-e Lasius niger americaims, Phcidolc dentata comutata, and 

 P. vinclandica. The cultivated food plants of this aphis are discussed at some 

 length. The species has been particularly injurious to corn in Maryland, Ohio, 

 Indiana, and Illinois and has done serious injury to this crop in eastern Penn- 

 sylvania, New Jersey, the Virginias, and the Cax'olinas. Its seasonal history 

 in other parts of the country does not appear to vary materially from that in 

 Illinois as described by Davis (E. S. R.. 20, p. 1051). Injury by a form of this 

 species to cotton, asters, and other cultivated food plants is also briefly discussed. 



Preventive measures include crop rotation, maintenance of soil fertility, early 

 plowing, followed by frequent cultivations, and the use of repellents. 



The paper concludes with a discussion of the Erigeron root-aphis {A. middle- 

 ioni), which has usually been identified with .4. maidl-radicis. "So far as is 

 now known A. middlefoni infests normally plants of the genera Aster and 

 Erigeron, usually in very large colonies at the crown of the plant just 

 below the surface of the ground or on the large roots. The only cultivated 

 plants it has been known to attack are Cosmos Inpinnatus and the China or 

 German asters {Callistephns horfensis), and possibly also dahlias and French 

 artichoke {Oynara scolymus)." Its food plants, attendant ants and experi- 



