REVISION MALACOSOIVIA HUBNER IN NORTH AMERICA 17 



The general procedure followed in collecting was to examine several 

 colonies in an area, checking for variation in larvae, egg masses, tents, 

 and hosts. If all colonies in the area were similar, a colony usually was 

 selected from the most common host, and the other hosts in the area 

 were recorded. If some colonies appeared to be different in some 

 respect, they were more carefully studied and appropriate ones were 

 selected for rearing. 



In some areas colonies were so numerous that any sample was bound 

 to include larvae from several egg masses, while in other areas colonies 

 were miles apart or impossible to find. An example of an area where 

 colonies were difficult to find is the west side of the Sierra Nevada 

 range south of Lake Tahoe. Not a single colony was located here 

 despite 2 days of driving through the area. Undoubtedly some were 

 present since they had occurred in outbreak numbers a few years 

 earlier (Clark, 1955, and Langston, 1957), but they evidently were 

 at a very low level in 1960 and we were not fortunate enough to find 

 any. This was the exception rather than the rule, however, and no 

 difficulty was encountered in locating at least a few tents in the vast 

 majority of the areas visited. 



Originally, it was planned to collect the larvae as soon after hatching 

 as possible and rear them to adults. Single colonies were to be col- 

 lected and reared to obtain some idea of the range of variation that 

 could be expected in both larvae and adults which presumably came 

 from a single egg mass. This plan, however, had to be abandoned for 

 several reasons, the most important of which was the introduction 

 into the insectar^'-trailer of a disease, tentatively identified as a non- 

 inclusion virus by Steinhaus (Steinhaus and Marsh, 1 962) , which made it 

 practically impossible to rear larvae from the earlier instars to adults. 



This disease afTected all instars of all species and subspecies reared 

 in the trailer, but little or no mortality was observed after pupation, 

 even though there can be little doubt that many of the larvae which 

 successfully pupated were infected to some degree. Collecting, there- 

 fore, had to be planned so as to obtain last instar larvae in order that 

 pupation would occur before the disease could progress to a fatal level. 



Although the collection of last instar larvae is advantageous in some 

 ways, it also has disadvantages. One advantage lies in easier collecting, 

 since the large tents of late instar larvae are readily spotted. Another 

 advantage is the shorter period of required feeding resulting in a 

 more rapid turnover of cage space and less work in feeding the larvae. 

 Also, larvae collected as last instars have been feeding on natural, 

 living hosts for the greater part of their larval life, while caged larvae 

 have been eating cut foliage that cannot be maintained in as good 



