May 5,1923 
Striped Sod Webworm 
409 
Tabi,E IV .—Record of food eaten, by larvce of Crambus mutabilis 
[I^inear millimetefs of blue-grass leaves, average width about 3 millimeters.] 
Instar. 
Maximtim. 
Minimum. 
Average. 
Number 
of larvae. 
IV. 
Mm. 
60 
135 
480 
I, 140 
576 
Mm. 
5 
50 
35 
90 
68 
Mm. 
33 
93 
183 
496 
268 
20 
20 
19 
18 
4 
V.. 
VI. 
VII. 
VIII. 
Total. 
i»o73 
The normal number of instars for mutabilis appears to be seven. 
Two larvae pupated from Instar VI, but neither lived until emergence. 
The males and females develop in very nearly the same time, showing 
a difference of only 0.2 of a day between the averages for 8 of each sex. 
The width of head and average length of the larva in each instar 
are shown in Table V. 
TABbE V.— Larval measurements of Crambus mutabilis 
Instar. 
Number 
Head width. 
Body 
measured. 
Maximum. 
Minimum. 
Average. 
length. 
I. 
8 
Mm. 
0. 194 
Mm. 
0. 194 
Mm. 
0. 194 
Mm. 
I. 77 
II. 
6 
.301 
.301 
.301 
2. 80 
Ill. 
4 
•459 
.424 
.441 
3. 08 
IV. 
5 
. 582 
•547 
•570 
5.00 
V. 
5 
.900 
. 812 
.847 
9. 00 
VI. 
II 
I. 306 
I. 166 
I. 227 
13.00 
VII. 
3 
I. 912 
I. 586 
I- 730 
18. 00 
DESCRIPTION 
Instar I.—^Head shining black, cervical plate fuscous, prothorax a little darker 
than abdomen, mesothorax and metathorax concolorous with it. Abdomen pale 
transparent yellow. Pinacula on thorax and abdomen dusky and conspicuous, 
unusually so for the first instar in this genus. 
Instar II.—Head shining black, frons deep fuscous, cervical plate castaneous, 
a little paler and more reddish than head. Rest of thorax and abdomen pale yellow. 
Pinacula dusky and conspicuous, for each is surrounded by a small area of brownish 
overcolor. 
Instar III.—Head shining black, frons paler, fuscous; cervical plate fuscous, rest 
of thorax and body pale, tinted by the ingested food, skin finely granular. Pinacula 
brownish, rugose, more or less conspicuously surrounded by a brownish area. Caudal 
plate pale with dusky dots. 
Instar IV.—[No description obtained.] 
Instar V. —Head dark yellow with clearly defined yellowish brown markings 
made up of round spots arranged in broken groups but in a definite pattern as follows: 
One area bordering the vertical suture and extending down on to the face in a branch 
each side of the frons; another larger triangular area with its base on caudal margin 
of head, extending forward until its tip joins the forks of the vertical spot; below 
this a smaller crescent-shaped area midway between the frons and caudal margin of 
