69 
RELATION TO THE CORN LEAF APHIS. 
Ever since Walsh, in 1862, doubtfully connected a leaf louse 
of corn, first reported by him,* with the root aphis described by 
Fitch from the roots of corn under the name of Aphis nmiais, t 
the relations of these insects has been a moot point, there has 
never been any evidence, however, of their connection as simply 
different forms of the same species other than the facts that 
they belong to the same genus, that they resemble each other 
more or less closelv in specific characters, and that they infest 
different parts of the same plant in the same territory, and often 
at the same time. On the other hand, the differences of specific 
character are such that they may very well belong to dirfeien . 
species, and should, indeed, have been held to be distinct uiuil 
their identity had been demonstrated. They do not by any 
means vary together in abundance either in time 01 m place, 
neither do "they by preference infest the same species of plant. 
The corn leaf aphis occurs much more abundantly on sorghum 
and broom corn, especially the former, than it does on Indian 
norn itself; while the root louse occurs but rarely on those plants. 
Many other species whose roots are infested by the root aphis 
have not been known to support the corn leaf aphis at any 
time. The bare possibility, however, that these two forms may 
nevertheless alternate in such a manner that the one may be de¬ 
rived from the other throws somedoubt on all propositions for an 
economic procedure, since if this is the case, both leaf and root 
louse must be taken into account in any measures intended to 
arrest the multiplication of either. 
On account of the economic importance of this point, elaborate 
experiments have been made necessary with both root and aerial 
lice. The distinctness of the two can only be shown by tracing 
the life history of each throughout the entire year under condi¬ 
tions such as to insure the production of the one from the other 
if such production be possible. Even then the demonstration 
would be incomplete unless both root and leaf lice had been fol¬ 
lowed generation bv generation throughout the entiie season 
-from the egg of one’year back to the sexual generation and the 
egg of another year. These experimental conditions have now 
been substantially fulfilled for the root louse only, as will be 
seen from what is presently to follow. The leaf louse, on the 
other hand, although it has been carried through the greater 
part of the year, including the entire fall and w inter season, has 
never yet been seen to produce a sexual generation or an egg„ 
Some experimental evidence has been obtained by attempting to 
bring the leaf aphis out of the root form by breeding the latter 
for many successive generations upon the corn leaf, and b\ sim¬ 
ilar attempts to rear the root louse from the winged leaf louse 
transferred to the roots of corn. These attempts have not thus 
* Proc. Ent. Soc. Phila., Vol. I. (1863), p. 300. 
+ Rep. Ins. N. Y., II.. p. 318. 
