REVISION MALACOSOMA HUBNER IN NORTH AMERICA 109 



to arid areas and should do quite well in many parts of California if it 

 were able to get there, and compete successfully with M. constrictum 

 which also prefers oaks. The limits of its eastward distribution are not 

 definitely known, but specimens have not been seen from areas farther 

 east than central Texas. It may occur farther east since many species of 

 oaks are present throughout most of the eastern United States. If it 

 does occur east of Texas, however, it is probably rare, and even more 

 rarely collected owing to its lack of a conspicuous tent. 



The factors which limit its eastward distribution are unknown, but 

 it does not seem to be limited by a lack of suitable host plants. Most 

 likely there are climatic factors which limit it since the eastern edge of 

 its known distribution more or less coincides with the transition zone 

 between the arid regions of western Texas and the more humid regions 

 of eastern Texas. In the Rocky Mountains it extends northward into 

 northern Colorado, but in the Great Plains it has not been collected 

 north of Texas, although it seems likely that it should be found in 

 Oklahoma or even farther north. 



ECONOMIC IMPORTANCE.— M. tigris does not appear to be of 

 any great economic importance, since it feeds on oaks, most of which 

 are of little value in the areas where it is known to occur. With tlie help 

 of M. disstria, however, it has caused heavy defoliation in south-central 

 Texas (see Coop. Econ. Insect Report, USDA, in recent years). In 

 fact, tigris was the more common species in many areas in Texas in 

 1961 and 1962, and was probably causing more damage than disstria. 

 Past reports of disstria causing heavy defoliation in Texas should be 

 regarded with caution, since tigris was probably also responsible in 

 many cases. 



COMMENTS. — The name "onissa'" is listed as a synonym of tigris 

 even though it differs from most tigris in some respects. In the holotype, 

 the outer margin of the forewing is bowed out at vein R5 more than 

 most Malacosoma, and the base of the eighth sternite is flared out 

 somewhat, but in other respects, such as the jagged accessory claspers, 

 it is like typical tigris. When more is known about the other life stages 

 of the Mexican Malacosoma it should be confirmed that ''onissa" is a 

 Mexican population of tigris which is somewhat different from the 

 more northern populations, but which intergrades with them. 



When the larvae of tigris are reared, the sex ratio of the adults is 

 approximately 1:1. But in collections of adults only, females are 

 extremely rare, only 7 females being found in a total of 411 adult 

 nonreared specimens examined in this study (7 females in the United 

 States National Museum were reared by Dyar). In one collection 

 made by Dr. Frederick H. Rindge of the American Museum of Natural 

 History near Monticello, Utah, in 1960, 125 males and no females 



