THE CITRUS WHITE FLY: SEASONAL HISTORY. 
81 
all individuals winter over as pupae. It should also be noted that 
the number of maximum degrees of effective temperature is more 
strongly influenced by the time of year the eggs are deposited — the 
nearer the winter months deposition takes place the fewer the degrees 
accumulating before the last fly emerges. This is due to the equal- 
izing effect of the cooler winter temperatures. 
This same equalizing effect of the winter temperatures upon the 
length of the life cycle for individuals developing from eggs laid on 
September 20 is brought out in Table XVI: 
Table 
XVI . — Duration 
of instar s of the citrus white fly. 
Instar. 
Speci- 
men 
No. 
First. 
Second. 
Third. 
Pupal. 
Total 
num- 
Duration of 
instar. 
Num- 
ber 
of 
days. 
Duration of 
instar. 
Num- 
ber 
of 
days. 
Duration of 
instar. 
Num- 
ber 
of 
days. 
Duration of 
instar. 
Num- 
ber 
of 
days. 
ber of 
days. 
1 
2 
3 
4 
5 
1908. 
Oct. 3-10 
Oct. 3-10 
Oct. 3-15 
Oct.3-Nov.2. 
Oct. 3-10 
8 
8 
13 
31 
8 
1908. 
Oct. 10-15.. 
Oct. 10-24.. 
Oct. 15-22.. 
Nov. 2-16.. 
Oct. 10-18. . 
5 
14 
7 
14 
8 
1908. 
Oct. 15-27 
Oct. 24-Nov. 10 
Oct.22-Nov.4.. 
Nov. 16-Dec.3.. 
Oct. 18-29 
12 
17 
13 
17 
11 
1908. 
Oct. 27- Apr. 28 
Nov. 10-Apr. 17 
Nov. 4-Apr. 8 . . 
Dec. 3-Apr. 6. . . 
Oct. 29-Mar.26. 
173 
158 
155 
128 
148 
198 
197 
188 
190 
175 
From this table it will be seen that retardation in growth during 
any one instar does not affect materially or show a corresponding 
increase in the total number of days required for development when 
the individual passes the winter in the pupal stage. Also, that an 
unusually large number of days spent in one instar does not neces- 
sarily mean that the individual insect will be equally backward 
in the next instar. These records of daily observation on individual 
specimens from hatching to adult are only 5 of 85 similar obser- 
vations for the same period. Nos. 2-5 were insects on the same leaf. 
SEASONAL HISTORY. 
Generations of the Citrus White Fly. 
It has been generally understood in the past that there are three 
generations annually of the citrus white fly, although Prof. H. A. 
Gossard, 1 states that ''four generations a year doubtless often occur, 
but not in sufficient numbers to obscure three well-defined broods 
as the rule." In the greenhouses at Washington, Riley and Howard 2 
found that there were but two generations annually. The life-history 
work of the present investigations has shown that while the general 
1 Bui. 67, Fla. Agr. Exp. Sta., p. 612, 1903. 
2 Insect Life, vol. 5, p. 224, 1893. 
59131°— Bull. 92—12 6 
