THE DESERT CORN FLEA-BEETLE. 
9 
The incubation period (Table II) varied from 3 days in the month 
of July and August to 15 days during March and April. The average 
time required for 314 eggs was 5.8 days. The egg stage was secured 
by placing freshly laid eggs within newly made plaster of Paris cages, 
the eggs being placed directly upon the plaster, which had been pre- 
viously darkened with waterproof India ink. This plaster not only 
kept the eggs sufficiently moist, but also kept down any fungous 
growth until the eggs could have time to hatch. Just previous to 
hatching the eggs darken slightly, taking on a yellowish tinge, and 
the larvae escape by bursting one side of the eggshell. 
Table II. — Length of egg stage of the desert corn flea-beetle ( Chaetocnema ectypa) at Tempe, 
Ariz., 1913, 1914, 1915. 
Cage No. 
Date 
laid. 
Num- 
ber. 
Date 
hatched. 
Num- 
ber. 
Length 
of incu- 
bation 
period. 
Aver- 
age 
mean 
tem- 
pera- 
ture. 
Bi 
1913. 
Aug. 27 
Aug. 28 
Aug. 29 
Aug. 30 
Sept. 7 
Sept. 19 
Sept. 29 
1914. 
Feb. 27 
Mar. 18 
Mar. 20 
1915. 
May 22 
June 12 
July 13 
July 22 
23 
24 
62 
75 
36 
5 
6 
20 
30 
15 
25 
25 
22 
23 
(Aug. 30 
{Aug. 31 
(Sept. 1 
/..do.... 
\Sept. 2 
/..do.... 
\Sept. 3 
Sept. 4 
Sept. 11 
Sept. 22 
Oct. 6 
Mar. 12 
(Mar. 28 
{Mar. 29 
(Apr. 1 
/Apr. 3 
I Apr. 4 
May 27 
June 17 
/July 16 
\July 17 
July 25 
1 
8 
14 
5 
19 
12 
40 
35 
36 
5 
5 
20 
17 
6 
3 
1 
7 
25 
25 
6 
16 
8 
Days. 
3 
4 
5 
4 
5 
4 
5 
5 
4 
3 
13 
10 
11 
14 
14 
15 
5 
5 
3 
4 
3 
°F. 
87 
85 
85 
85 
84.3 
81 
81 
81 
87 
83 
71 
61 
64 
63.5 
62.6 
61 
61 
74.6 
80 
86 
86 
85 
Ci 
Di 
Ei 
Hi 
Li 
Mi 
2 
3 
4 
T 141 
T163 
T2392 
T360* 
Totals and average 
391 
314 
5.8 
'R. N. Wilson's records. 
"* L. J. Hogg's records 
THE LARVA. 
DURATION OF LARVAL PERIOD. 
It was quite easy to secure the approximate length of the larval 
stage of many specimens, but owing to the feeding habits, a great 
deal of difficulty was experienced in securing the exact length of this 
stage. Various types of cages were first tried, all of them embodying 
the feature that the larvae must be beneath the surface of the ground 
in order to insure their reaching maturity. In the past two years, 
however, the experiment was modified by placing the newly hatched 
larvae upon small tender sections of corn root, within the cavity of 
57154°— Bull. 436—17 2 
