12 BULLETIN 1336, TJ. S. DEPARTMENT OF AGRICULTURE 
Table 5. — Lengths of larval instars of the green clover worm 
Instar 
Number 
reared 
Instar lengths 
Maximum 
Minimum 
Average 
First . 
33 
33 
33 
33 
33 
33 
Days 
4 
4 
3 
5 
6 
14 
Days 
2 
2 
2 
2 
2 
5 
Days 
3.09 
2.21 
2.36 
3.27 
3.64 
8.27 
Second . __ 
Third 
Fourth 
Fifth 
Sixth 
Total 
9 2 84 
In the course of the larva's growth the size of its head increased 
with each molt but remained constant throughout each instar, thus 
forming a reasonably safe guide for determining the instar. Table 
6 gives the head widths by instars from numerous measurements. 
Table 6. 
— Head widths of green clover 
worm larvae 
at different stages 
of growth 
Instar 
Number 
measured 
Width 
Maximum 
Minimum 
Average 
First - 
6 
6 
10 
11 
11 
5 
Millimeters 
0.285 
.459 
.753 
1.166 
1.586 
2.052 
Millimeters 
0.265 
.353 
.635 
.886 
1.306 
1.866 
Millimeters 
268 
403 
Third 
713 
Fourth 
996 
Fifth 
1.454 
Sixth 
1 940 
The measurement of the length of the caterpillar can also be used 
to some extent to indicate the instar, although the degree of individual 
variation in length is much greater than for the head width. Table 
7 may be used as a guide in this respect. 
Table 7. — Larval lengths of the green clover worm at different stages of growth 
Length of larva 
Instar 
Maximum 
Minimum 
Average at 
end of in- 
star 
Average at 
beginning 
of instar 
First .- . - 
Millimeters 
4.0 
7.5 
11.0 
19.0 
23.0 
31.0 
Millimeters 
1.5 
3.5 
8.0 
11.0 
16.0 
18.0 
MUlimeters 
3.58 
6. 55 
" 10. 17 
15.59 
20.68 
28.60 
Millimeters 
1.50 
3.58 
Third 
6.55 
Fourth 
10. 17 
Fifth 
15.59 
Sixth 
20.68 
RESISTANCE TO FROST 
The larva? of Plathypena scdbra are known to survive ordinary 
frosts, but eventually succumb to continued cold weather. None 
have been found alive in the field in the vicinity of Nashville, Tenn., 
later than October 18. W. R. McConnell reported finding numerous 
live larvae in a plot of soybeans at Greenwood. Miss., as late as 
