REVISION MALACOSOMA HUBNER IN NORTH AMERICA 133 



adult 441 's emerged between 29 June and 2 July, and adult 442's 

 emerged between 30 June and 5 July, indicating that there was no 

 important difference in developmental rates, although those on aspen 

 were a few days later on the average. This same situation was found 

 at other localities (309, aspen vs. 310, Ribes; 443, aspen vs. 444, Ribes; 

 449, aspen vs. 448, Ribes), where there was no great difference in the 

 stage of development between populations found on aspen and those 

 foimd on Ribes. All of this means that there is little chance of isolation 

 between the 441 's and 442's due to differences in adult emergence 

 dates, but suggests that there may be some isolation between the 44 la's 

 and the other two, since no 441a larvae were found at the time the 

 44rs and 442's were collected. 



The only other area where three similar populations were found in 

 the same immediate locality was 8 miles north of Boulder, Garfield 

 County, Utah. Collection 438 (with specks) was taken from bitterbrush, 

 Purshia tridentata, and Collection 439 (without specks) was taken from 

 chokecherry. In addition, notes were taken indicating that Collection 

 439 was similar to colonies found on aspen at the same site. This 

 situation was similar to that just described from Bryce Canyon National 

 Park except for the following minor differences. The egg masses of the 

 BS's (438) were laid on both twigs and large branches, and the egg 

 masses of the B's (439) were like those found on aspen except that they 

 were laid on larger branches as well as on twigs. The BS larvae were 

 more mature than the B larvae, even though they were shaded during 

 part of the day. However, emergence dates of the adult B's were earlier 

 than the BS's, ranging from 3 to 6 July. The BS adults emerged from 

 6 to 10 July. This is just the opposite of what should have happened, 

 since the BS's were more mature when they were collected. Possibly the 

 difference is due to the fact that the BS's could not be reared on their 

 native host after collection, while the B's could be reared on choke- 

 cherry. No matter what the reason is, it points out the importance of 

 making observations on developmental rates under field conditions if 

 at all possible, since many factors which affect development under field 

 conditions cannot be duplicated in the laboratory, and other factors 

 which may be of little importance in the field may become important in 

 the laboratory. After all, it is the emergence dates of adults under field 

 conditions which determine whether any gene exchange is possible 

 between different populations which would otherwise be capable of 

 interbreeding. 



These comparisons were made on limited numbers of colonies from 

 only two localities, and they were made on preserved specimens since 

 the existence of specks in the spumaline was not known when the 

 collections were made. Therefore, more extensive field observations 



