THE BLACK FLY OF CITRUS. 11 
tance of 30 feet from these orange trees a young palm, Eleais 
melanococca, was found to be lightly infested and adults were seen 
flying away from it toward the orange trees when disturbed. Hence, 
it is evident that this palm was the source of reinfestation of the 
orange. 
m At Corozal in October, 1918, four lime trees in front of what was 
once the old post office (house 543, now used as quarters for attend- 
ants at Corozal Asylum) were found lightly infested with A. woglumi. 
Across the road, behind the houses opposite Corozal Asylum, on a 
long open lawn space, was a row of 29 lime trees, none of them 
infested, the nearest being at least 300 feet from the four infested 
trees. After the first week of heavy rains following the dry season 
(Apr. 24, 1919) all trees were reinspected. The infested trees showed 
a decidedly heavier infestation and of the row of limes uninfested 
in October, 1918, trees Nos. 9, 10, 20, 25, 27, 28, and 29 were found 
. infested. Tree No. 1 was the farthest away (about 900 feet) from 
the source of infestation and trees Nos. 20 to 29 the nearest (200 to 
300 feet away) to it. Trees Nos. 20 to 25 were almost directly 
opposite the originally infested trees. That this was a recent infesta- 
tion was shown by the fact that no individuals were found beyond 
the pupal stage and no adults had emerged from any of the pupse 
found. In July this row of trees was again examined and trees 
Nos. 9, 10, 11, 12, 18, 20, 23, 25, and 29 were found infested and 
the infestation was increasing. It is evident that the infestation of 
numbers 11 and 12 came from trees Nos. 9 and 10 and that of 18 
came from tree No. 20. The infestation on Nos. 27 and 28 had 
died out for some reason. Here we have an infestation due directly 
to the flight of adults, the longest flight being about 700 feet and 
-^the least 200 feet. 
It has been noted in bringing adults into the laboratory on shoots 
on which they had gathered in abundance in the field, that when 
such shoots wilted the adults would leave them and fly out of the 
screened windows, a case of forced migration guided by positive 
phototropism. 
Likewise in working around trees on which adults were clustered 
in the late afternoon it has been observed that when disturbed many 
of the adults take to flight and, instead of merely flying off a short 
distance and returning to the trees as they often do, a large number 
would disappear permanently. 
4 No observations have been made as to whether or not the insect 
is carried by the wind. Nor has there been seen any such migration as 
Morrill and Back (21, p. 44-48) have described as taking place in 
the case of the citrus white fly (Dialeurodes citri Ashmead). This is 
probably due to the fact that no large and heavily infested citrus 
