90 UNITED STATES NATIONAL MUSEUM BULLETIN 276 



Hardy (1943) reported a similar avoidance of buffaloberry, Shepherdia 

 canadensis, and silverberry, Eleagnus argenta in British Columbia, but 

 again the leaves were used as cocoon sites. 



The pear appears to be the only fruit tree which has some immunity 

 among those that disstria might be expected to attack. Treherne (1913) 

 reported that in British Columbia disstria and [californicum] pluviale 

 "feed upon almost everything in the orchard except the pear, which 

 under normal conditions seems immune." Downing et al. (1956), how- 

 ever, list both of these species as being sporadically injurious to pear 

 in British Columbia. In the present study it was not possible to get 

 any species to feed on pear. Possibly some cultivated varieties of pear 

 are immune, but others may be acceptable in varying degrees. There 

 may be a few other species of trees or shrubs immune to attack by 

 disstria, but a lack of acceptable hosts does not appear to be a factor 

 limiting its distribution. 



TYPE. — Apparently destroyed. Dr. F. Kasy of the Naturhistorisches 

 Museum, Vienna, Austria, could not find it in their series of Malaco- 

 soma disstria Hiibner, and states that it is highly unlikely that it could 

 be found in any other collection. 



TYPE LOCALITY. — Unknown, probably somewhere in eastern 

 North America. 



DISTRIBUTION (fig. 1). — M. disstria is the most widely distributed 

 North American species, occurring throughout most of the United 

 States and Canada wherever deciduous trees grow. No specimens from 

 Mexico have been seen, but it seems likely that it occurs there, since 

 its distribution extends into southern Texas and New Mexico. 



ECONOMIC IMPORTANCE.— Af. disstria is without doubt the 

 most destructive North American tent caterpillar because of its wide 

 distribution, wide host range, and the relatively frequent outbreaks 

 which occur on economically important species such as aspen, gum, 

 oak, and maple. 



COMMENTS. — ^There have been numerous subspecies, varieties, 

 aberrations, etc., proposed for M. disstria, but Dyar (1928) was 

 correct when he said, "The various varietal names proposed are 

 superfluous, referring to individual variations only." Extensive dis- 

 sections of specimens from all over North America have shown that 

 disstria can be distinguished from all other North American species by 

 characters such as the epiphysis and genitalia. These characters are 

 constant for all subspecies, varieties, etc., which have been described. 

 The various described forms were based originally on differences in 

 adult or larval coloration, but, as far as is known, none of these color 

 variations are restricted to any geographic area, so there is no basis 

 for any subspecific designations. 



