506 



less dependent on this tree. Of these only 37 per cent, derive their food 

 from sohd substances of the tree, the rest feeding on the juices of the 

 tree, on fungi, etc. In the present paper only those species are dealt 

 with which jive in the cambium, belonging to the families Scolytidae, 

 Cerambycidae, Anobiidae, Curculionidae and Buprestidae. 

 The only Scolytid that is always a primary pest is Dendroctonus 

 micans, Klug, which is, however, very rare in Finland. The most 

 common species is Ips typographus, L., and groups or single trees are 

 often found which apparently have been killed by this insect. The 

 fact that /. typograpkus is better known than the other bark-beetles 

 of spruces renders it very probable that this species is often accused 

 of the death of trees which have in reality been killed by others. 

 Next to /. typographus in importance come Pityogenes chalcographuSy 

 PolygrapJius poligraphus and P. subopacus, which are also found on 

 perfectly healthy trees. The latter species is regularly found, together 

 with 7. typographus, usually in the upper part of the tree, though it 

 often attacks small spruces from the root to the top. P. poligraphus 

 and P. subopacus can only with difficulty be distinguished from one 

 another and from the third Finland species P. punctifrons, Thoms. 

 The latter, however, seems to prefer fallen trees, whereas the others 

 mainly attack standing ones. In company with these species Xylechinus 

 (Kissophagus) pilosits, Ratz., occurs on the mountain slopes, especially 

 in the northern parts of the country. 



The following species are comparatively rare, but may occasionally 

 be dangerous : — Pityophthorusfennicus, E., occurring on the trunk and 

 branches of weak standing trees, measuring about 2-6 inches in 

 diameter ; Ips duplicatus, Sahib., only occurring on trunks cut off 

 about 3|-5 feet above the ground, but found also on one occasion on 

 a healthy tree ; Ips suturalis, Gyll., wliich seems to prefer trees damaged 

 by fire, and Cryphalus saltuarius, Weise, which is fairly common in the 

 northern part of the country, where, especially on the mountain slopes, 

 it kills the small trees. Still more rare, but probably as dangerous 

 as the above, axQ Pityogenes saalasi, E., Phloeophthorus [Phthorophloeus) 

 spinulosus, Rey, and Cryphalus abietis, Ratz. Other species that 

 are very common, but do not play any important part because they 

 are secondary pests, are Hylastes palliatus, Gyll., Crypturgus pusillus, 

 Gyll., C. hispidulus, Thoms., and C. cinereus, Herbst. The following 

 species only occur in fallen trees or stumps and are consequently of 

 little or no importance, viz : — Polygraphus punctifrGns, Thoms., 

 Hylastes cunicuiarius, Er., H. glabratus, Zett., Ips laricis, F., Dryocoetes 

 autographus, and D. hcctograplius, Reitt. 



Of the Cerambycidae the following three species are very common 

 and primary in character of attack : — Tetropium castaneum, L., 

 T. fuscum, F., and Callidium. coriaceum, Payk. Tetropium makes the 

 pupal chamber rather close to the surface, while Callidium often 

 penetrates the wood to the centre. Tetropiimi seems to prefer the 

 lower part of the trunk and is very often found in trees where Ips 

 typographus has attacked the rest of the trunk and Pityogenes chalco- 

 graphus the top and the branches. Although the larvae of these beetles 

 are very common, the imagines are comparatively rare, because the 

 Ivarae have so many enemies, both Hymenopterous and Dipterous, as 

 well as wood-peckers, which diminish their number before they pupate. 

 €aenoptera minor and Seynanotus undatus, which live in slender trees, 



