THE BLACK FLY OF CITRUS. 21 
but the injury seemed to be due to neglect and to the fungus (Gloeo- 
sporium gloeosporoides) , which had gained entrance to the trees 
through pruning wounds. At Corozal the injury seemed to be 
due to heavy infestations of the purple scale (Lepidosaphes beckii 
Newm.), and of the West Indian red scale [Pseudaonidia (Selenaspi- 
dus) articulatus Morg.]. These dying lime trees were not heavily 
infested with A. woglumi. 
In the authors' work at Ancon, Balboa, and Cristobal, it was found 
that when citrus trees (lime, orange, and grapefruit) were heavily in- 
fested with the two scales mentioned above, they were almost invaria- 
bly only lightly infested with A. woglumi even though they were in close 
proximity to trees heavily infested with this insect. From the authors' 
experience then it would seem that the infestations of scale insects and 
the black fly go on independently of each other and it does not neces- 
sarily follow "that an infestation of the black fly is invariably accom- 
panied by rapidly increasing scale infestations so that the life of an 
infested tree is necessarily short" (25). That this may take place 
is not denied, but that it has not taken place in the Canal Zone to 
date is the result of a year's observation in that region. It has also 
been observed that heavy infestations, especially of the West Indian 
red scale, serve as a decided inhibition to the development of the 
black fly, as will be pointed out under the life history of the insect. 
The writers find that the two scales mentioned do far more actual 
and noticeable damage than the black fly in that they actually kill 
infested areas on the leaves and cause infested twigs to die. In 
many instances the cultural conditions and neglect to which trees 
have been subjected are in themselves sufficient to injure them 
seriously even if no insect or fungous pests were involved and such 
factors coupled with a heavy infestation of the black fly doubtless 
will, in time, prove a handicap that these trees will be unable to over- 
come in spite of the fact that the climatological conditions of this 
region are extremely favorable to plant development. 
Since in all the survey work conducted by the authors a tree was 
never found killed by the black fly, it is safe to conclude that much 
of its injury is "ornamental" and that the fact that it makes heavily 
infested trees decidedly unsightly has been largely responsible for 
the exaggerated statements regarding its destructiveness. 
In conclusion the authors' work bears out the following statements 
of Morrison, who has seen the insect and its injury in the Canal Zone, 
Jamaica, and Cuba: "It may be said that the presence of this pest in 
numbers affects adversely the infested tree, and may in cases where 
other factors are also unfavorable be the final handicap which pre- 
vents the production of a crop of fruit or reduces it in size until it is 
unprofitable commercially to grow such a crop, or prevents the trees 
from making the amount of new growth each year which is necessary 
