116 UNITED STATES NATIONAL MUSEUM BULLETIN 2 76 



Table 3. — Numbers of colonies of M. americanum and M. californicum 

 lutescens found at localities between Guthrie and Perkins, Oklahoma. All 

 colonies were found on wild plum. 



From this table it can be seen that in a distance of approximately 

 15 miles (6 miles NE. Guthrie to 7 miles E. of the Cimarron River) 

 there is a complete replacement of M. californicum lutescens by M. 

 americanum. Both species were sufficiently abundant to defoliate many 

 of the wild plum thickets along the highway. Both species appear to 

 have nearly identical requirements. Both lay their eggs in the same 

 way, prefer wild plum, build the same kind of tent, and seem to be 

 very much alike in other respects. The only thing noted to be different 

 in the field situation was the more nearly mature condition of the 

 c. lutescens caterpillars. Most of them were in the last instar, but most 

 of the americanum were only in the next to last instar or early last instar. 

 It is not known whether this is due to a difference in hatching dates, 

 different developmental rates, a different number of instars, or some 

 other factor, but tlie end result is the same — c. lutescens matures sooner 

 than americanum. This possibly could be advantageous during years of 

 very high populations since the faster maturing c. lutescens conceivably 

 could starve out the slower maturing americanum by consuming all the 

 available foliage before any americanum larvae were large enough to 

 pupate. Even a few days difference could be critical, since last instar 

 larvae eat about four times as nmch foliage as all the earlier instars 

 combined (Hodson, 1941). Hodson's work was done on M. disstria, 



