NORTH AMERICAN BUPRESTID BEETLES 165 



indicated but in a few examples they are entirely obliterated, and 

 rarely there are two vague costae on each elytron. The concavity on 

 the second abdominal segment of the male is not constant, and it 

 varies from a narrow, parallel sided groove, to one that is distinctly 

 wider in front than behind, but in all cases the first segment is 

 broadly concave, and the bottom roughly sculptured. 



Hosts. — This is the most serious pest of the European white birch, 

 particularly the cut-leaved form, but it also attacks our native birches 

 and poplars, especially when cultivated for ornamental purposes. 

 Swaine (1918) reports that about 50 per cent of the white birches 

 have been badly injured in the Province of Quebec, and in some of 

 the parks in the United States practically all of the birches have 

 been killed. It has been reared from yellow birch (Betula lutea 

 Michaux), black or sweet birch (B. lenta Linnaeus), paper birch 

 (B. papyrifera Marshall), red birch (B. fontinalis Sargent), gray 

 or white birch (B. populifolia Marsh), European white birch (B. 

 alba Linnaeus) and its cut-leaf form, aspen (Populus tremidoides 

 Michaux), large-tooth aspen (P. grandidentata Michaux), cotton- 

 wood (P. deltoides Marshall), Carolina poplar (P. deltoides pilosa 

 (Sargent) Sudworth), balsam poplar (P. bdlsainifera Linnaeus), 

 northern black cotton wood (P. trichocarpa hastata Henry), balm-of- 

 gilead (P. balsamifera candicans (Aiton) Gray). Cook (1890) and 

 Davis (1891, 1892) record this species as making galls on pussy 

 willow {Salix discolor Muehlenberg), but the writer has not seen 

 any specimens from this host. Turner (1918) records it from pecan, 

 but this record was made without any doubt from an incorrectly 

 identified specimen. 



This species has received considerable attention from the economic 

 entomologists, due to the great amount of injury caused to orna- 

 mental birches in the southern part of Canada and northern part 

 of the United States, and is commonly known as the " bronze birch 

 borer." 



Chamberlin (1926) records the species from southern California, 

 but this is incorrect, as the specimen mentioned in the collection of 

 the Academy of Natural Sciences of Philadelphia is not this species. 



LeConte separated anxius from gravis from the fact that the 

 groove on the head is deeper and longer, the prehumeral carinae 

 less distinct, the elytra with a vague discal costa, and the pronotum 

 more brassy than the elytra, but all of these characters are variable, 

 and all forms of intermediates can be found in a series of specimens. 

 Horn (1891, p. 307) states that both torpidus and gravis were de- 

 scribed by LeConte from females, but on examining the types in the 

 LeConte collection torpidus (No. 10 in the anxius series) is a male 

 which agrees with his description of that species and which was 



