8 



root or to another root close by, and there watched over by the patient 

 and industrious ants. The same thing- was observed going on about 

 a young plant of fox-tail grass in this same cornfield. 



INFLUENCES LIKELY TO PRODUCE FEMALES. 



While the production of winged individuals seems to be brought 

 about largely by insufficient food supply, Forbes is of the opinion that 

 the production of egg-laying females is fully as much — if not indeed 

 much more — influenced by the temperature, a low temperature caus- 

 ing them to be produced at an}' time, regardless of generation; and he 

 .himself has secured them from as many as five different generations. 

 In two cases recorded ])y him the first 3'oung produced developed to 

 adults that gave birth to their 3'oung, whereas the last developed to 

 adults that laid eggs. These cases, although seeming rather out of the 

 ordinar}", illustrate the fact that the insect may adapt itself to widel}' 

 different autumn conditions; that is to say, an early frost, which pre- 

 supposes a low temperature, kills the corn but does not annihilate the 

 insect, for an egg-laying generation is thus precipitated and the ants 

 promptl}' secure the eggs. This egg-la3'ing' generation is probabl}' 

 produced in September or October, as these females are found in the 

 burrows of ants at that time. Possibl}' it is produced earlier to the 

 South. Mr. C. N. Ainslie, of this Bureau, one of the writer's assist- 

 ants, found the egg -laying females quite numerous in such situations 

 on September 22, at Annapolis Junction, Md. The chief item of 

 interest to the farmer is the fact that these e^^gs are taken charge of 

 by the ants and kept through the winter. 



THE ant's CAEE FOR EGGS AND YOUNG OF THE ROOT-APHIS. 



There is no indication that the ants hunt the fields for egg-laying 

 females; on the contraiy, they secure their supply of eggs from females 

 kept for precisely that purpose in their burrows about the roots of 

 corn. This affords ample explanation of the increasing abundance of 

 root-aphides in fields that are cultivated to corn 3'ear after 3'ear in 

 succession, and it also points to a preventive measure. The object of 

 all of this care on the part of the ants is to obtain from the root-aphis 

 a sweet fluid known as "honey dew." Owing to this peculiar rela- 

 tion, this and some other aphides are commonl}' termed "ants' cows."' 

 Thus the economic importance of this insect and its association with 

 ants is for practical purposes fully accounted for and an explanation 

 furnished as to why farmers are misled into believing that it is the 

 ants that actually destroy the corn. Not only this, but a condition of 

 affairs is revealed which shows why this. 3^oung growth of grass and 

 weeds that springs up soon after the ground is plowed in spring, pre- 



[Cir.86] 



