60 UNITED STATES NATIONAL MUSEUM BULLETIN 276 



Adults emerging from cocoons collected by Hodson (1941) showed a sex 

 ratio for M. disstria in Minnesota of 47 percent females in 1 936 and 48 

 percent females in 1937. Similar unpublished sex ratios taken by Hodson 

 in 1952 showed 30 percent females at Lake George, Minnesota (7 mi. 

 E. Itasca State Park), 38 percent females in 1953 at Lake George, and 

 43 percent females in 1953 just north of Itasca Park. All of these results 

 consistently show fewer females than males, and if it is assumed that the 

 samples were random and there are no other differences between males 

 and females which result in greater numbers of one sex being collected 

 than the other, it indicates one of two things : either the females had a 

 higher mortality rate at some time during their development, or there 

 were fewer females at the start. It is not known which of these alterna- 

 tives (or both) is true. 



The pluviale-lutescens Relationship 



The number of unhatched, dead caterpillars, infertile eggs (those eggs 

 which contain only yellow or orange yolk and show no signs of any 

 embryological development), and other unhatched eggs (those eggs 

 showing signs of some development, but which are not recognizable as 

 caterpillars because they died at an early stage of development or be- 

 cause they were decayed) do not appear to be of any significance in any 

 of the egg masses with the exception of rearings R27 and R36. When 

 these are compared with their reciprocals (R28 and R35) and the con- 

 trols (R29 and R30), the number of infertile eggs is strikingly greater in 

 R27 and R36. 



In both R27 and R36 the male parent came from populations about 

 100 miles east of Edmonton, Alberta, which have been known since 

 1949 as M. lutescens (Neumoegen and Dyar), the so-called prairie tent 

 caterpillar (figs. 373-375, 221). Before 1949 it had been known as M. 

 fragile lutescens (Neumoegen and Dyar). The female parents came from a 

 population in the foothills of the Rocky Mountains about 60 miles 

 northwest of Calgary, Alberta, that has been known in the past as a bog 

 form of M. pluviale (Dyar), the so-called western tent caterpillar (figs. 

 372, 200). (See the section on M. calif ornicum pluviale for a discussion of 

 the bog form and crossing it one way with nonhog pluviale, page 158, 

 It would have been better to use nonbog pluviale since they are more 

 likely to occur in the same area as lutescens, but their emergence could 

 not be synchronized with that of lutescens.) 



Often infertile eggs which are found in egg masses of Malacosoma 

 are grouped together, indicating that the sperm probably were pre- 

 vented from reaching these eggs for one reason or another, rather than 



