THE CITRUS WHITE FLY: LIFE HISTORY AND HABITS. 
63 
PUPAL STAGE. 
One of the most interesting phases of life-history studies has been 
the wide range in the duration of the pupal stage; a range of from 13 to 
304 days. Considering the relatively slight variation in the length of 
the larval life, this range among specimens passing into the pupal 
stage at practically the same time is remarkable. In view of the fact 
that the effect of this variation upon the duration of life and number 
of annual generations will be fully discussed under those headings and 
brought out in Tables XV and XVII and figure 12, only a few of the 
large number of records on file are given in Table X to illustrate this 
range in pupal life during different parts of the year. 
Table X. — Duration of pupal stage of the citrus white fly. 
Speci- 
men 
No. 
Period of growth. 
Num- 
ber of 
days. 
Sum of 
effective 
tempera- 
tures. 
Speci- 
men 
No. 
Period of growth. 
Num- 
ber of 
days. 
Sum of 
effective 
tempera- 
tures. 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
Apr. 30-May 13 . 
Apr. 30-June 20 
Apr. 30-Aug. 3 
May 18-June 5 
May 18- July 31 
Mayl8-Mar. 18 
July 15-July 30 
July 15-Aug. 4 
Aug. 15-Aug. 27 
Aug. 15-Aug. 28 
13 
51 
64 
18 
74 
304 
15 
20 
12 
13 
410 
1,833 
2,564 
664 
2,866 
11 
12 
13 
14 
15 
16 
17 
18 
19 
20 
Aug. 15-Sept. 6 
Aug. 16-Mar. 18.... 
Aug. 16-Mar. 20.... 
Aug. 17-Mar. 25 
Aug. 18-Sept. 10... 
Aug. 18- Apr. 1 
Sept. 30-Mar. 31... 
Oct. 28- Apr. 19.... 
Nov. 1-Apr. 17 
Nov. 8-Mar. 25.... 
22 
214 
216 
220 
23 
226 
182 
173 
167 
137 
885 
5,414 
5,479 
5,574 
931 
5,752 
4,473 
4,167 
4,069 
3,256 
602 
808 
479 
521 
It will be noticed that pupae pass either a comparatively few or a 
comparatively large number of days in this stage and that ordinary 
temperatures and humidity do not have the oower to determine which 
it shall be. 
LOCOMOTION. 
On hatching from the egg the young larva is provided with well- 
developed legs, as shown in figure 5, by the aid of which it crawls 
about the leaf for several hours and then settles and begins to feed. 
Because of the aimless way in which it crawls, frequently doubling 
on its own course and turning aside for the least obstacle, it travels 
over a very limited area. It is therefore improbable that the crawling 
larvae ever leave the leaf upon which they were hatched, unless carried 
on the feet of birds or insects or blown or dropped from one leaf to 
another. After settling, the larva does not change its position on the 
leaf, while with the first molt its legs become vestigial (see fig. 7) and 
unfit for locomotion. Larvae frequently move slightly, especially 
directly after or during molting when they merely describe an arc 
of 180°, using their mouth parts as a pivot. The larva passes into the 
pupal stage without materially changing its position on the leaf. The 
only time, then, during the life cycle when the white fly is capable 
of moving about from place to place is during the winged adult stage 
and the crawling larval stage. 
