CONTRIBUTIONS ON THE CORN ROOT-APHIS. 107 



up and the contents so scattered that the ants are able to recover only 

 a few of their own eggs and larvae, and fewer yet of the aphis eggs. 

 This method also prevents the weeds from getting a start, so that 

 there is no food for the young larva? which hatch from those eggs 

 which the ants are able to preserve. This is a good treatment for 

 land that is to be planted to corn throughout the section of country 

 where the root-aphis is found, but more especially in the northern 

 part of the infested territory. 



In the more southern part of the range of this insect winter plow- 

 ing may be practiced with good results wherever the land is suffi- 

 ciently level so that it will not wash badly. Winter plowing breaks 

 up the ants' nests and scatters the contents of these nests at a time 

 when the ants are least able, because of the cold wet weather and 

 shortness of the food supply, to recover from the injury. 



One example of the effects of winter plowing that came under the 

 observation of the Bureau of Entomology was as follows : Mr. John 

 Bowie, at Annapolis Junction, Md., plowed the major portion of a 

 60-acre field in the winter of 1905-6, leaving unplowed a small strip 

 in the middle, which he finished in the spring. Prof. F. M. Webster 

 visited this field July 28, 1906, and found that owing to injuries by 

 the root-aphis the spring-plowed portion of the field would almost fail 

 to produce a crop, while the winter-plowed portion gave promise of 

 an unusual yield. On the spring-plowed area much of the corn was 

 missing, while many of the surviving stalks were dwarfed. By these 

 signs it was easy to determine at a glance the dividing line between 

 the two areas. On September 22, 1906, just after the corn was cut 

 and shocked, this field was visited by Mr. C. N. Ainslie, and he, too, 

 was able clearly to separate the two areas, being guided only by the 

 appearance of the stubble. 



In the southern part of its range the corn root- aphis is able to 

 spend the entire summer on its wild food plants, and these wild 

 plants are especially infested in the late summer and early fall. If, 

 then, these weeds are destroyed by thorough cultivation, the root- 

 aphis is encouraged to leave the fields. In the fall eggs are laid on 

 the roots of late scrub corn which was not harvested and on the roots 

 of weeds such as Ambrosia and pigweed. Fall plowing as soon as 

 possible after' the crop is harvested will prevent these eggs from being 

 laid in the field. The land may then be put into some cover crop. 



REPELLENTS. 



The method of combating the root-aphis by direct application of 

 repellents to the seeds was investigated by Doctor Forbes and re- 

 ported in the Twenty-fifth Report of the State Entomologist of 

 Illinois. Many substances were experimented with, such as oil of 

 lemon, oil of cloves, kerosene, and carbolic acid. Of these, oil of 



