254 



fir, Pityophthorus spp. occurring in the branches ; /. ( T.) bidentatus' 

 and Pityogenes spp. in the branches of pine, with /. {T.) sexdentatus 

 in the trunk. 



A blocking of the sap-flow, which results in decomposition, occurs 

 after defoliation, which may be due to insect infestation. Injury to 

 the crown, as is seen in stumps standing in windbreaks, is also respon- 

 sible for this condition, and it occurs in trunks that have been 

 felled and deprived of their branches in early spring. Such damp 

 timber attracts the following beetles :^ Hylesinus palliatus and Ips 

 {Tomicus) autograph us in spruce ; Cryphalus piceae in fir ; Myelophilus 

 spp., Hylastes spp., and Hylesinus palliatus in pine. /. {T.) lineatus 

 appears in spruce and fir if the wood is damp enough to ensure the 

 formation of the fungus la3'er in the mines. 



The preparation of trap-trees must be carried out on this basis. 

 For standing trap-trees, two rings are cut round the trunk, with a space 

 of a hand's-breadth between them. The bark between the rings may 

 be left (double ringing), or it may be removed (girdling) ; the crown of 

 the tree may be sawn off, or the branches may be lopped off. In spite 

 of the high attractiveness of standing trap-trees, they are not often used, 

 because their preparation is troublesome, the attack and development 

 of the beetles are difficult to observe, and, especially, because a period 

 of from one to two years elapses before attractiveness begins. For 

 practical work felled trunks are used as traps. Their attractiveness 

 may be increased materially by scarif3dng their upper surfaces 

 longitudinally, the resulting resinous odour attracting species such as 

 Hylastes, Pissodes and Hylohius. In such a scarified trunk the brood 

 often fails to develop because the bark soon dries and large numbers 

 of parasitic and predaceous enemies appear. 



The position of the tree and the character of its surroundings are 

 important factors in the selection of a trap-tree. The season of the 

 year must also be considered. Trees felled in winter usually become 

 attractive in the following flight period, whereas trees felled in spring 

 or early summer are rarely ready in the same year, and by the next 

 season are already too much decomposed to prove attractive. 



The following data apply to a region with an average annual tempera- 

 ture of 42°-46°F., where felling is done in winter, where girdling 

 standing trees is not much practised, and where beetles occur in normal, 

 abundance. 



Spruce. Hylastes cunicularius : Double rings a few months before 

 felling, removal of strips of bark after felling, examination of the 

 side touching the ground after a few months ; in sheltered positions 

 the branches must be lopped off ; in exposed ones they must be left. 

 H. palliatus : Felled trunks with branches in exposed situations and 

 lopped in protected places ; standing trunks without crowns or entireh- 

 lopped. Polygraphus poligraphus : Girdled trees to be felled in spring,. 

 the branches being left and strips of bark removed ; standing trunks 

 to be girdled or double-ringed ; these require a long time to become 

 attractive, but then become very effective. Ips (T.) chalcographiis : 

 Faggot-wood or billets are best ; felled trunks must be lopped except 

 in shaded situations ; standing trees must be girdled or double-ringed. 

 /. {T.) amitinus : Felled trunks with branches; standing trees to 

 be double-ringed. /. [T.) typographus : Trees, preferably girdled 

 in the previous autumn, must be felled in winter or early spring, 

 ungirdled ones must be scarified ; in exposed situations they must be 



