12 BULLETIN 1336, U. 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 



Third 



2 36 



Fourth 



3 27 



Fifth 



3 64 



Sixth 



8 27 







Total 



22.84 













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 

 0.268 





.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 





Maximum 



Minimum 



Length of larva 



Instar 



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 



Millimeters 

 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 







EESISTANCE TO FROST 



The larva? of Plathypena scabra 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. K. McConnell reported finding numerous 

 live larvse in a plot of soybeans at Greenwood, Miss., as late as 



