THE CITRUS WHITE FLY: SEASONAL HISTORY. 81 

all individuals winter over as pup. 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 terkperatures upon the 
length of the life cycle for individuals developing from eges laid on 
September 20 is brought out in Table XVI: 
Taste XVI.—Duration of instars of the citrus white fly. 











Instar. 
Speci- First. | Second. Third. | Pupal. Total 
men —— page 
No. | ber of 
Num- Num- Num- Num-| days. 
Duration of | ber | Duration of | ber Duration of ber Duration of ber 
instar. of instar. of instar. of instar. of 
days. | days. days. | days. 
| | | 
| 
1908. 1908. 1908. 1908. 
ae ov Oct. 3-10.-..- S | Oct. 10-15. - 5 | Oct. 15-27 : 12 | Oct. 27-Apr. 28) 173 198 
2S eae Oct. 3-10...-- 8 | Oct. 10-24_. 14 | Oct. 24-Nov. 10 17 | Nov. 10-Apr. 17 158 197 
Cae OCs). a 5- isi Olwigs oe ae. 7 | Oct. 22-Nov. 4. 13 | Nov. 4-Apr. 8 ..| 155 188 
ARs, Oct. 3-Nov. 2- 31 | Nov. 2-16... 14 | Nov. 16-Dee. 3.. 17 | Dee. 3-Apr.6..-| 128 190 
aye ae Oct. 3-10... -- 8 | Oct. 10-18. - 8 | Oct. 18-29. .__-- 11 | Oct. 29-Mar. 26. 148 175 
| 



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. 
SEASONAJ 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,' states that ‘‘four generations a year doubtless often occur, 
but not in sufficient numbers to obscure three well-defined broods 
as therule.” In the greenhouses at Washington, Riley and Howard ? 
found that there were but two generations annually. The life-history 
work of the present investigations has shown that while the general 
1 Bul. 67, Fla. Agr. Exp. Sta., p. 612, 1903. 
2 Insect Life, vol. 5, p. 224, 1893. 
86850°—Bull. 92—11——6 
