REVISION MALACOSOMA HUBNER IN NORTH AMERICA 19 



1962) as a noninclusion virus, was extremely troublesome. Apparently it 

 was picked vip somewhere in northern California while the insectary- 

 trailer was located at Albany on San Francisco Bay — a relatively cool 

 area. No diseased larvae were noticed while the trailer was located 

 there, and none were noticed after the trailer was moved to Hat 

 Creek in Lassen County, California, until about a week after the temp- 

 eratures began climbing into the 90s every day. At that time many 

 larvae began to show disease symptoms and died several days later. 



Presumably many of the caterpillars had become infected when the 

 trailer was at San Francisco Bay, where temperatures were too low to 

 permit a general outbreak. Thus, the disease was well established 

 before its presence was suspected and there was little that could be 

 done to disinfect effectively the entire trailer once the disease reached 

 epidemic proportions. 



Larvae from most of the collections made while the trailer was at 

 San Francisco Bay had pupated, were pupating, or were in the late 

 last instar when the disease reached an epidemic level. As previously 

 noted, once the larvae have pupated, little mortality occurs, so it was 

 possible to obtain adults from most of these collections. Collections in 

 which all the larvae died before pupation were either similar to other 

 successfully reared collections, or they were replaced v/ith more mature 

 larvae obtained on a second trip to the original localities. Most col- 

 lections made after the disease became a problem contained late 

 instar larvae, so they were successfully reared. 



From the economic viewpoint this disease was highly effective in 

 controlling tent caterpillars under insectary conditions, where the 

 cages were protected from the weather, and it v/as easy for the wind 

 to blow dry, contaminated dust throughout the trailer. Under field 

 conditions, however, the effectiveness of the disease undoubtedly 

 would be considerably reduced. 



The following symptoms characterize this disease. Infected larvae 

 cease to feed, but continue to wander about very actively until they 

 begin to shrivel and shorten. At this stage the anal prolegs begin to 

 become useless and a piece of moist, soggy frass usually protrudes 

 from the anus. As the disease progresses the body shortens even more 

 and the anal prolegs become completely useless and upturned. In- 

 fected larvae regurgitate large amounts of a reddish-brown fluid when 

 they are touched or distiirbed. This regurgitation, combined with the 

 loss of fluids through the soggy piece of frass and the lack of replace- 

 ment by feeding undoubtedly accounts for the rapid shrivelling and 

 shortening of the body as the disease progresses. In the final stages the 

 larva is unable to crawl or cling to any support, and eventually falls to 

 the ground. Mature larvae that normally would be nearly 2 inches long 



