976 
Journal of Agricultural Research 
Vol. V, No. 21 
CAUSE OF PRODUCTION 
The theory has been frequently advanced that the production of 
winged forms during the summer is due to a lack of sufficient nourish¬ 
ment for the insects. In some cases the wording of this theory is modified 
by the statement that winged forms appear on plants which are very 
heavily infested. The writers’ results are a flat contradiction of this 
theory for this species. 
As has been stated previously, in handling the insects the writers 
always transferred the mothers to new plants, rather than the progeny. 
In this way several consecutive generations were reared on one plant. 
Thus the effect of poor or good food would be accentuated. Yet the 
winged forms were never obtained in series of small, poorly fed insects, 
but occurred frequently in well-nourished series. 
It should be stated that these results are not based on deliberate 
experiments to obtain data on this point. Notes were made simply 
because of a very evident abnormality in size and rapidity of develop¬ 
ment, correlated with a lack or an abundance of food. Later, in study¬ 
ing the notes, it was found that the large, well-fed insects developed 
rapidly and often produced winged forms, while many of the small, 
starved aphides produced only wingless progeny. Moreover, none of the 
plants was heavily infested, so the production of winged aphides can 
not be correlated with that condition. 
In addition to the foregoing data, it was found that those winged 
insects produced during the summer months showed little or no inclina¬ 
tion to leave the plants on which they were produced. This would at 
once disprove the theory that these winged forms are produced when 
the insect meets adverse food conditions in order to carry it to better 
food. 
Other writers have maintained that the winged insects were produced 
as the result of an abundance of certain chemicals in the soil. The 
writers’ work would not certainly contradict this theory. Still, the 
fact that the soil used was mixed in large batches and that winged forms 
were produced on some of the plants, while other plants raised in soil 
from the same batch bore only wingless forms would seem to cast con¬ 
siderable doubt on its truth. It is also very difficult to understand how 
the occurrence of such a form as an intermediate could be made to con¬ 
form to this theory. 
The writers’ results, deduced from very full notes on the life history 
of this aphis, lead to the belief that much of the evidence given in favor 
of these theories is based on insufficient data. 
It seems much more probable, especially in view of the quite frequent 
occurrence of such a form as the intermediate, that the production of 
this winged form during the summer is merely a reversion from the 
wingless to the more primitive aphis form. As such it is doubtful 
whether food conditions have anything whatever to do with the matter. 
