4 BULLETIN 427, U. S. DEPAETMENT OF AGRICULTUKE, 



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 locahty 

 in the tubers, these would be left behind. 



When aU these facts are considered, there is some argument in 

 favor of considering America as its native home.^ 



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 confuies 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 kiUs 

 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 usuaUy 

 dies. It is easy to see that wherever this occurs generally over a 

 field while the potato plants are yomig 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 first 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. 



