22 
BULLETIN 1393, U. S. DEPARTMENT OF AGRICULTURE 
THE EGG 
INCUBATION PERIOD 
Data on the incubation period of the granary weevil accompanied 
by the maximum, minimum, and mean temperatures for the period, 
have never been published. References to the length of the egg 
stage are very fragmentary except those by Strachov-Koltchin 
(65), in which the day, but not the night, temperatures are given. 
This writer concludes that the incubation period may range from 
about 5 days at 75° F. to 15 days at 62° F. Observations made on 
individual eggs indicated that at 75° F. the incubation period might 
be 5 to 6 days; at 73° and 82° F., 6 days; at 69° F., 8 days; at 68° 
F., 9 days; and at 67° F., 9 to 10 days. 
Table 4. — Duration of the egg stage of the granary weevil 
Date egg 
laid 
Date egg 
hatched 
Temperature 
for incubation 
period 
Length 
of egg 
stage 
No. 
Date egg 
laid 
Temperature 
for incubation 
period 
Length 
of egg 
stage 
No. 
S 
a 
I 
X 
a 
a 
a 
3 
a 
ca 
Date egg 
hatched 
a 
03 
3 
a 
3 
a 
a 
i 
a 
OS 
9 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
17... 
1919 
Sept. 30 
Oct. 1 
Oct. 2 
Oct. 3 
Oct. 15 
1920 
Mar. 18 
Mar. 25 
Mar. 26 
Mar. 28 
Apr. 9 
Apr. 13 
Apr. 16 
Apr. 20 
June 23 
June 26 
July 3 
July 14 
July 15 
July 20 
July 24 
Aug. 5 
Sept. 1 
1919 
Oct. 5 
...do 
Oct. 6 
Oct. 7 
Oct. 19 
1920 
Mar. 24 
Mar. 31 
Apr. 1 
Apr. 3 
Apr. 15 
Apr. 18 
Apr. 21 
Apr. 25 
June 27 
June 30 
July 7 
July 18 
July 20 
July 24 
July 28 
Aug. 9 
Sept. 5 
°F. 
98 
98 
98 
98 
94 
90 
95 
95 
95 
85 
90 
92 
93 
93 
93 
96 
94 
94 
94 
95 
93 
96 
OF- 
67 
68 
68 
67 
67 
54 
52 
58 
55 
46 
46 
54 
62 
66 
70 
68 
68 
70 
68 
69 
68 
°F. 
79.8 
78.0 
83.1 
83.1 
80.4 
69.7 
76.8 
77.5 
78.1 
66.6 
68.7 
76.1 
78.9 
79.9 
78.6 
82.9 
81.0 
81.3 
81.5 
80.5 
80.2 
81.6 
Days 
5 
4 
4 
4 
4 
6 
6 
6 
6 
6 
5 
5 
5 
4 
4 
4 
4 
5 
4 
4 
4 
4 
23. 
24 
25. 
26.... 
27.... 
28.... 
29. 
30™. 
31.... 
32.... 
33.... 
34. 
35. 
36.... 
37____ 
38____ 
39.... 
40.... 
41____ 
42.... 
43.... 
1920 
Sept. 2 
Sept. 3 
Oct. 5 
Nov. 7 
Nov. 12 
Nov. 15 
Dec. 4 
Dec. 15 
Dec. 16 
1921 
Jan. 11 
Jan. 21 
Jan. 23 
Jan. 31 
Feb. 2 
Feb. 3 
Feb. 11 
July 26 
July 30 
Aug. 2 
Aug. 15 
Sept. 26 
1920 
Sept. 6 
Sept. 8 
Oct. 12 
Nov. 13 
Nov. 17 
Nov. 20 
Dec. 19 
Dec. 25 
Dec. 24 
1921 
Jan. 20 
Jan. 30 
Feb. 1 
Feb. 12 
Feb. 14 
Feb. 15 
Feb. 23 
July 30 
Aug. 3 
Aug. 6 
Aug. 20 
Oct. 1 
°F. 
96 
95 
89 
88 
79 
76 
84 
84 
84 
80 
84 
84 
88 
88 
88 
86 
°F. 
68 
68 
50 
57 
57 
39 
35 
35 
35 
34 
43 
43 
43 
39 
39 
39 
°F. 
81.5 
82.8 
70.9 
72.1 
68.5 
62.9 
61.0 
60.0 
61.2 
61.2 
62.6 
64.0 
67.6 
66.2 
66.5 
65.2 
85.4 
81.5 
83.5 
76.5 
72.5 
Days 
4 
5 
7 
6 
5 
5 
15 
10 
8 
9 
9 
9 
12 
12 
12 
12 
4 
18 
4 
19 
4 
20 
21 
22 
86 
83 
69 
65 
5 
5 
Of the data presented by the writers in Table 4, those for 1919 
and 1920 were secured under the semi tropical conditions of Florida 
and those of 1921 under laboratory conditions at Washington, D. C. 
These data indicate that the minimum period for egg development 
is 4 days when the temperature means average about 78° to 80° F. 
The longest incubation period, 15 days, recorded in Table 4, covers 
a period when the daily temperatures ranged from a minimum of 
35° F. to a maximum of 84° F., with a mean of 61° F. But at a 
mean of 60° F., with the same range in the maximum and minimum 
temperatures for the period, one egg (No. 30) required only 10 days 
for development. Certain eggs held for 28 days in refrigeration at 
