THE CITRUS THRIPS. 
11 
INCUBATION PEEIOD. 
The time required for the development of the egg after deposition 
varies considerably at different times of the year and is influenced 
largely by the prevailing temperature. There is also some variation 
among eggs deposited the same day, in the same plant, and kept 
under precisely the same conditions of temperature. The incubation 
period ranged from a minimum of 6 days to a maximum of 21 days, 
the average for the entire season being 16 days. The records on 
incubation in 1911 are given in Table II. The principal average 
seasonal variations, together with the prevailing mean temperatures 
for the periods covered, are shown in Table III. It will be seen that 
in the cool weather of spring and early summer and again in the fall 
the incubation period is about two and one-half times as long as in 
the hottest period of summer. In like manner the egg stage and 
other immature stages as well are short in exceptionally hot, dry 
summers, such as those of 1908 and 1909, and considerably prolonged 
in cooler years, such as 1911. 
Table II. — Incubation period of the citrus thrips, Lindsay, CaL, 1911. 
Rec- 
Num- 
ord. 
ber of 
No. 
eggs. 
1 
11 
2 
61 
3 
15 
4 
6 
5 
2 
6 
1 
7 
1 
8 
1 
9 
8 
10 
31 
11 
2 
12 
11 
13 
7 
14 
5 
15 
3 
16 
1 
17 
1 
Deposited. 
May 4 
do 
do , 
do 
do 
do 
do 
....do 
May 5 
do 
....do 
May 6 
do 
....do 
....do 
....do 
May 9 
Hatched. 
May 21. 
May 22. 
May 23. 
May 24. 
May 25. 
May 26. 
May 27. 
May 28. 
May 21. 
May 22. 
May 24. 
May 22. 
May 23. 
May 24. 
May 25. 
May 27. 
May 25. 
Dura- 
Rec- 
Num- 
tion of 
ord 
ber of 
stage. 
No. 
eggs. 
Days. 
17 
18 
1 
18 
19 
1 
19 
20 
1 
20 
21 
1 
21 
22 
1 
22 
23 
2 
23 
24 
1 
24 
25 
1 
16 
26 
1 
17 
27 
1 
19 
28 
1 
16 
29 
3 
17 
30 
2 
18 
31 
2 
19 
32 
1 
21 
33 
1 
16 
Deposited. 
May 9 
.../.do 
do 
July 17 
do 
July 22 
do 
do 
Aug. 1 
do 
Sept. 6 
Sept. 8 
do 
do 
Sept. 18 
do 
Hatched. 
May 26.. 
May 27. . 
May 28. . 
July 23.. 
July 24.. 
July 28. . 
July 29. . 
Julv 30. . 
Aug. 9 . . 
Aug. 10 . 
Sept. 23. 
Sept. 21. 
Sept. 22. 
Sept. 24. 
Oct. 8... 
Oct. 10.. 
Dura- 
tion of 
stage. 
Days. 
Maximum . 
Minimum. 
Average . . . 
Days. 
.. 24 
Table III. — Principal seasonal variations in incubation of 
thrips, Lindsay, Cal., 1911. 
of the citrus 
Period of season. 
Range. 
Average. 
Mean 
tempera- 
ture. 
May 4 to May 28.. 
July 17 to Aug. 10 
Sept. 6 to Oct. 10. 
Days. 
16-24 
6-9 
13-22 
Days. 
18.8 
7.3 
17.0 
° F. 
64.06 
81.52 
62.18 
