8 UNITED STATES NATIONAL MUSEUM BULLETIN 276 



Malacosoma incurvum incurvum (Henry Edwards) — raised to species 

 Malacosoma incurvum discoloratum (Neumoegen)— raised to sub- 

 species 

 Malacosoma incurvum aztecum (Neumoegen) — regarded as a sub- 

 species 



In figure 2 note that the six subspecies of M. calif ornicum occur at the 

 edges of the distributional range. In the center between the subspecies 

 a large area is occupied by populations that are highly variable. None 

 of the subpopulations within this area are regarded as being sufficiently 

 distinct to warrant formal recognition, so they are referred to as M. 

 californicum. The following terminology has been adopted, however, to 

 distinguish between these central populations and the species as a 

 whole, including the subspecies. The name "M. californicum''^ is used to 

 refer to the species when it is not necessary to distinguish between sub- 

 species and other populations. The name "M. californicum (central 

 populations)" is used when referring to all populations except the sub- 

 species. 



Unless specifically stated otherwise, it can be assumed that inter- 

 mediate and intergrading populations are present wherever the distri- 

 butions of subspecies adjoin. 



Economic Importance of the Genus Malacosoma 



In North America tent caterpillars have been known as pests of vari- 

 ous shrubs and trees since the earliest colonial times. Britton (1935) 

 gives a brief history of outbreaks in New England of M. americanum, the 

 eastern tent caterpillar, and states that "at least in 1646, the pest was 

 exceedingly abundant, as it has been in certain other seasons." Epi- 

 demic populations of Malacosoma disstria, the forest tent caterpillar, are 

 recorded in eastern North America as early as 1791 (Baird, 1918). 

 Sippell (1962) mentions an outbreak described by Paul Kane in 1834 

 which may be the earliest record of an outbreak in Canada of Malaco- 

 soma disstria, the forest tent caterpillar, although it is not definitely 

 established that M. disstria was the insect responsible. 



All species of North American tent caterpillars either have been 

 recorded in the literature as occurring in outbreak numbers or per- 

 sonally have been observed to do so during the field seasons that were 

 spent studying them in the western United States and Canada. Some 

 recent outbreaks have occurred in areas that are relatively undisturbed 

 by man. Examples of such outbreaks are those of M. disstria and M. 

 tigris in the scrubby oak forests of central Texas, M. constrictum in the 



