4 BULLETIN 427, U. S. DEPARTMENT OF AGRICULTURE. 
one, since the change always favors its being freed from some of its 
natural enemies and checks. This is especially true of the tuber 
moth, since most of its parasitic enemies aid in reducing it only when 
it appears as a leaf miner, and if it were introduced into a new locality 
in the tubers, these would be left behind. 
When all these facts are considered, there is some argument in 
favor of considering America as its native home. 1 
NATURE OF INJURY. 
Injury by the tuber moth is accomplished through two widely dif- 
ferentiated methods of attack : (1 ) To the growing plant, and (2) to the 
tuber (fig. 1). The injury to the plant is incident to the mines in the 
leaf and petiole and to the tunnels in the stem. As a rule the egg 
is deposited on the leaf, and the larva as soon as hatched starts to 
mine in the leaf. As the larva grows the leaf becomes too thin for 
mining, and if there is not another leaf near by to tie up, the larva 
either rolls the leaf or enters the petiole. If the larva confines its 
work to the leaves it injures one-third to one-half a leaf during its 
larval life, but where necessity drives it to mining the petiole it kills 
the entire leaf. Once started in the petiole the larva rapidly works 
its way to the main stem, which it begins to tunnel. (Fig. 2.) 
The larva generally works downward in the stem, although in a very 
few cases where the stem is thick and succulent it may turn and work 
upward. Wherever a larva works within the stem for several days 
before becoming mature the terminal section of the stem usually 
dies. It is easy to see that wherever this occurs generally over a 
field while the potato plants are young considerable injury might 
result through the reduction of leaf surface and a weakening of the 
plants. 
A factor which would make this possible would be the stacking of 
a large amount of infested potatoes from the firs*t crop near fields 
where the second crop of potatoes was just beginning to come up. 
Only one instance of this type of injury has been noted, although in 
1912 conditions were as bad as they would ever be allowed to become. 
In one small field (about 7 acres) at least half of the plants were 
materially injured and the yield was probably reduced one-fourth to 
one-third. The moths were very abundant in this field at the time 
the potato plants were coming up, and several could be found on 
each plant. The reason that more injury was not caused was prob- 
ably due to the fact that vigorous young potato plants are quick to 
grow away from any injury. 
1 Notwithstanding the opinions above expressed there are, perhaps, equally good reasons for supposing 
that this species is of exotic origin, and since it was first reported in New Zealand it would be natural to 
look to that vicinity for its natural habitat. It has been somewhat generally credited with being native 
to North Africa, and with reason, since the flora of that continent is particularly rich in solanaceous plants. 
In fact, the tropical regions of Africa and South and Central America include among their native plants 
nearly nine hundred species of Solanaceae. — F. H. Chittenden. 
