THE BLACK FLY OF CITRUS. 39 
of her. Attempts to induce mating between individuals of known 
history were all unsuccessful, due to the nervousness of these indi- 
viduals when confined. 
When confined the adults seem to be positively phototropic and 
always gather at the side of the cages where the light is brightest. 
% It is perhaps this reaction to light that guides them to the young 
growth of the tree, but once they reach this growth they invariably 
gather on the undersides of the leaves and avoid light, for if a shoot 
on which adults have gathered is turned so that the undersides of 
the leaves are exposed to strong light the adults immediately become 
nervous and wander around to the opposite side of such leaves. 
The length of life of adults is extremely hard to determine. Kept 
in glass vials with and without moisture some individuals of unknown 
previous history have remained alive as long as three days, though 
the large majority died within the first 36 hours. When allowed to 
emerge from pupae on leaves kept in petri dishes individuals have 
lived as long as four days. Out of large numbers of males and 
females (approximately 800) on young shoots, brought into the labora- 
tory from the field and placed in water, a few individuals have re- 
mained present as long as fire days before taking to flight, and on 
emerging from pupa cases in life-history spirals in the laboratory 
several females have remained within a few millimeters of the pupa 
case from which they emerged as long as six days and as short a time 
as two hours before flying away. Hence, it may be assumed that 
the life of the adults is at least a week and that it may be -as long as 
12 days, i. e., by adding the maximum time that they have remained 
near the pupa case and the maximum time that they have remained 
on the young shoots. 
£ TECHNICAL DESCRIPTION. 
The following technical description based on material from the 
Canal Zone has been prepared by Dr. A. C. Bakerund Miss Margaret 
L. Moles, of the Bureau of Entomology. 
EGG. 
Plate XI, A. 
Size 0.208 mm. by 0.08 mm.; shape elliptical, curved, with the stalk short and 
attached some distance from the base. Color yellowish, surface apparently without 
reticulations in some cases and with them in others, due, no doubt, to the structure 
being destroyed in boiling. When present they average 0.006 mm. in diameter. 
FIRST LARVAL INSTAR. 
Plate X, A. 
Size averaging 0.304 mm. by 0.192 mm.; shape elliptical, broadest just cephalad 
of the middle pair of spines. Margin very minutely serrate; abdominal segments 
distinct but narrow; vasiform orifice oval, almost entirely filled by the operculum. 
Caudal margin with two pairs of prominent spines, the outer pair measuring 0.032 
