THE BLACK FLY OF CITRUS. 23 
these were removed. The chosen spirals were observed daily, or 
three times daily in many instances, until the life cycle was com- 
plete. Hence by close observations in the field and by a careful 
study of the habits of the insects in all stages in the laboratory, 
answers to most of the questions mentioned before, and which could 
not be determined by the direct method, have been obtained. 
Two methods were used in obtaining the life history of this insect, 
namely, the group method and the individual method. Both had 
certain advantages and disadvantages. The group method con- 
sisted in taking an egg spiral laid on a known date, watching for the 
eggs to hatch, and then making observations on the individuals from 
one to three times daily until they had completed their life cycle. 
In this case, however, only the number of individuals that passed 
from one instar to another on a given date was recorded day by day. 
The individual method consisted in accurately plotting the egg spiral 
and the position of the larvae after they had settled and giving each 
one a number to be retained by it throughout its development. The 
time when each molted was then recorded, thus giving a very accurate 
record of the development of each individual. The advantage of the 
group method is that it is a rapid one and shows readily by a glance 
at the chart how many individuals die in a given instar, the duration 
of a given molt, and the time of the maximum molting for a given 
molt. (See fig. 5.) From such a chart the life-history curve of the 
individuals of one lot of eggs can be plotted directly. The great 
objection to this method is that it does not give a clear-cut individual 
record, which is also desirable. The advantages and disadvantages 
of the individual records are just the inverse of the group record, but 
the chief objection in the work here was that this method was too 
slow and there was in many cases a waste of time due to the great 
mortality of A. woglumi, especially in the first instar, as will be shown 
later. The two kinds of records taken together make an ideal com- 
bination, as one can be used to interpret the other. 
The following tables are representative of the two methods of 
recording the life history and show the range and variation under 
favorable (field) conditions and more or less unfavorable (laboratory) 
conditions. In the laboratory the small trees used were watered 
daily, but the humidity was often as much as 20 per cent lower in- 
doors than out-of-doors, and there was generally a considerable breeze 
blowing through the room. Likewise the light in the room was dull 
and it seems that all the factors taken together retarded the indi- 
viduals, especially in the pupal stage. But laboratory data give a 
clue to the ability of the species to adapt itself to its environment 
and likewise indicate what takes place in the dry season, especially 
in a region like Las Sab anas. 
