20 BULLETIN 885, U. S. DEPARTMENT OF AGRICULTURE. 
in the Canal Zone there is always a steady breeze blowing which 
naturally increases transpiration from the leaves. This increased 
transpiration, coupled with the drain .on the sap supply due to the 
insects, caused the wilting and subsequent dropping of the leaves so 
that by April, 1919 (the end of the dry season) (PL. I, B) , fully 75 per 
cent of the total number of leaves were lost. This loss of leaves, how- 
ever, seemed to be a benefit to the tree, for when a leaf wilted it 
checked the development of all stages of the black fly occurring on it 
and when it fell large numbers of the insects were killed, as is shown 
by experiments on the effects of drying on the emergence both of 
larvae from eggs and of adults from pupae. Likewise, the rate of 
reinfestation from April to September, 1919, has been very slow, 
due to the fact that practically all heavily-infested leaves were shed. 
But this tree is far from being dead, and with the coming of the wet 
season in the middle of April, it put forth an abundance of new 
growth, the greater part of which was free from woglumi, so that 
one not knowing its previous history would scarcely suspect that it 
had been one of the most heavily-infested trees found in the Caoal 
Zone. 
The observations on this tree were checked against those made on 
both orange and tangerine trees heavily infested with A. woglumi in the 
Las Sabanas region of Panama. Here the trees were unwatered, but 
the fact that they were of considerable size, close together, and pro- 
tected by windbreaks, offsets this factor. The percentage of leaves 
lost Was not as great as in the case of the tree at Ancon, due no doubt 
to a checking of the development of the black fly during the dry 
season so that the infestation at the end of the dry season was notice- 
ably less than at the beginning. There was nothing here to indicate 
that either the quantity or quality of the fruit had been seriously 
reduced by the black fly. 
In several instances in the outlying parts of the Las Sabanas region 
various kinds of citrus that were well cared for, but received water 
only at long intervals or not at all, were found to be in a badly wilted 
condition, but examination showed them to be entirely free from 
woglumi. Such trees, however, seemed able to resist the drought 
much better than infested ones and did not lose as large a percentage 
of leaves. On the other hand, trees in the same region and likewise 
uninfested but neglected in every way were found to be decidedly 
dwarfed in size and many were dead and dying. These same condi- 
tions were verified in the Canal Zone. 
In the village of Taboga on the island of that name, lime trees 
growing under very adverse conditions and heavily infested showed 
some injury but not as much as might have been expected. 
At Frijoles and Corozal dead and dying lime trees were found. 
At the first place neither scale insects nor the black fly were present, 
