108 PAPERS ON CEEEAL AND FORAGE INSECTS. 



lemon appears to be most promising. A solution of the oil in alco- 

 hol — 1 part of the oil to 9 parts of ordinary commercial alcohol — is 

 used. About 3 ounces of this mixture is used to a gallon of corn. It 

 should be stirred thoroughly till all the seed is moistened. This 

 treatment costs only 10 cents an acre for the materials, and appears 

 to be very effective. 



INJURY TO COTTON. 



A form of Aphis maidi-radicis was very injurious to young cotton 

 on the light sandy soil of the eastern parts of North Carolina and 

 South Carolina throughout the seasons from 1907 to 1909. During 

 this time it was the most injurious enemy of cotton in that region. 

 In this form, which is apparently the same as that found on corn at 

 Duncan, Okla., by Mr. T. D. Urbahns, of this Bureau, the spots on 

 the back of the apterous vivipara are larger and darker than they 

 are on the typical Aphis maidi-radicis as found on corn roots in 

 Illinois. The third antennal segment has two or three circular sen- 

 soria which are not present in the Illinois variety. Although this 

 insect AYas first brought to the attention of entomologists as a cotton 

 pest in 1907, some of the cotton planters in North Carolina have 

 known of it for upward of twenty years. 



It attacks cotton just as soon as the young plants appear above 

 ground and is usually first noticed when the plants are about 2 inches 

 high. The cotton plants in certain areas will turn red and die, 

 shriveling up so that they can be seen with difficulty. In one field, 

 examined May 28, 1909, at Marion, S. C, by Mr. G. G. Ainslie, fully 

 90 per cent of the cotton was infested. As a rule most of the aphides 

 observed were in a cluster on the main stem just below the surface 

 of the ground, but a few could be found anywhere on the roots, even 

 to the tips of the longest rootlets. Mr. Ainslie found as many as 

 200 insects, in all stages, on one plant. 



As far as the study of this insect has gone it appears that the 

 root-aphis infests cotton only while the plants are young and tender, 

 and leaves as soon as the roots begin to get hard and woody ; or they 

 remain only on the fibrous rootlets deep down in the soil where they 

 are unable to do much damage. They leave the plants as winged 

 migrants or are transferred by the ants to some of the numerous 

 wild food plants of this species. 



The ravages of this insect in the cotton fields can be largely pre- 

 vented by proper rotation and better culthation. Most of the 

 planters reported that the insect was less injurious where cotton was 

 grown after cotton. This is because the cotton fields are usually well 

 cultivated, so that when the root-aphides leave the cotton plants they 

 leave the cotton fields, and their eggs are not left in the fields in the 

 fall. 



