66 



Dendroctonus borealis Hopk.; U.S. Bur, Ent., The Genus Dendroctonus^ 

 133, 1899. 



The length varies from 5 mm. to 7 mm.; long series from the Rockies 

 and Lesser Slave Lake are as large as the average of obesus, while from some 

 localities the size is usually smaller; the punctures of the elytral striae are 

 usually small and rather indistinct, but very many individuals have these 

 dorsal punctures quite as coarse as in typical specimens of obesus; the elytral 

 strise are more constantly distinctly impressed, but in this character also 

 there is great variation. Much of our material from the southern Rockies, 

 the Selkirks and the southern interior of British Columbia agrees with 

 the characters given for engelmanni Hopk., but the intergradation with the 

 typical borealis is so complete that the name borealis is employed for all 

 our variations discussed here from Alberta and the interior of British 

 Columbia. 



Host trees. — White Spruce, Engelmann's Spruce. 



Distribution. — Alaska, the Yukon, throughout the interior of British 

 Columbia and northern and western Alberta. We have also taken it in 

 white spruce in northern Manitoba. 



Economic importance. — An important secondary enemy and frequently 

 a serious primary enemy to white and Engelmann's spruce throughout its 

 range. Incipient outbreaks should not be neglected. It has killed a large 

 amount of timber in Northern Alberta. 



Dendroctonus piceaperda Hopk.; Bur. Ent., U. S. Dept. Agric. Bui. 28, N.S., 

 p. 16. 



This species is very closely allied to the obesus-borealis series. The 

 head and pronotum are entirely as in borealis and obesus, with similar 

 slight variations. The elytral strise are usually distinctly impressed and 

 the punctures of the discal strise are usually rather coarse and distinct. 

 The size is usually smaller than in borealis and obesus; a series from New- 

 foundland is constantly 5 mm. long; and another long series from Sydney, 

 N.S., varies between 5-75 mm. and 6-2 mm. The writer has taken 

 borealis, with small discal punctures, as far east as northern Manitoba; 

 when long series are available from the region between Manitoba and 

 northern Quebec, the relations between borealis and piceaperda can be 

 discussed more satisfactorily. Individual specimens of piceaperda are 

 best separated by the rather coarse and deep strial punctures of the disc 

 and the deeply impressed strise, but exactly the same conditions are 

 commonly found in our series from the northern Rockies and Alberta. 



The egg-tunnels are longitudinal, usually short, in the inner bark, 

 grooving the wood surface; the eggs are closely placed in rather large 

 groups, alternately, on the tunnel wall; the larval mines usually separate 

 at a short distance from the tunnel; they are exposed in the inner bark 

 and the pupal cells are usually exposed. 



Host trees. — Red, White, and Black Spruce. 



Distribution. — Michigan and central Pennsylvania (Hopkins), north- 

 wards through Maine and the Maritime Provinces to Newfoundland. 



Economic importance. — This species is one of the most destructive 

 in the genus. It has killed enormous quantities of spruce, particularly 

 in Maine and south western New Brunswick. 



Dendroctonus obesus Mannh.; Bull. Mosc, p. 296, 1843; Hopkins, U.S. Bur. 

 Ent., The Genus Dendroctonus, p. 135, 1909. 



Length, 5-5 mm. to 7 mm., the average about 6-5 mm. The colour 

 when mature is usually deep black, rarely reddish. The punctures of the 

 discal strise are usually coarse and distinct; the shape is frequently slightly 

 more elongate than is usual in borealis, with the hairs often denser, but 



