COLEOPTERA SCOLYTID^E. 87 



soon afterwards dies. In nearly all cases the female dies at the end 

 of the burrow, after the deposition of eggs. 



In a general way the appearance of many species of insects is very 

 much affected by climatic conditions, and the Scolytidaa are especially 

 susceptible to the influence of weather. Thus the first appearance of 

 the hibernating species in spring depends on the warmth and sun- 

 shine. The weather also affects the swarming of the brood, and the 

 colour of the beetle is therefore sometimes variable, as specimens 

 which swarm soon after changing from the pupal to the perfect stage 

 are light as compared with those fully developed specimens which, on 

 account of unfavourable weather, have had to remain for a consider- 

 able time within the food-plant. The markings, too, are sometimes 

 affected, as the perfect beetles, in their quarantine stage, often make 

 markings beyond the pupal recesses. 



These remarks apply to the markings of a typical bark-beetle ; but 

 the student, we repeat, must make a very careful study of the mark- 

 ings, because they are so definite in character that from them alone 

 the species can always be determined. 



It must also be borne in mind that there is a sharp and definite 

 distinction between certain species which feed on conifers and others 

 which feed on hardwoods, inasmuch as we never find coniferous 

 feeders living in hardwoods and vice versa. This distinction, how- 

 ever, applies to species, and not to genera. For example, take the genus 

 Cryphalus. Thus C. abietis and 0. picece feed on spruce and silver fir 

 respectively, while C. fagi and C. tilim live on beech and lime. 



The various parts of the tree itself also harbour different species, 

 and therefore several species may be found on one tree. Take, for 

 example, a comparatively young Scots pine tree. In the top twigs we 

 may have Pityogenes bidentatics, and in the smaller branches Hylastes 

 palliahis. The stem may harbour Hylurgus {Hylesinus) piniperda, 

 and the root-surface Hylastes ater. 



The mother-gallery is a- most important character, and no illustra- 

 tion is quite complete unless it is shown. The mother-gallery, as 

 a rule, is either perpendicular or horizontal that is to say, it is 

 perpendicular when running in the same direction as the standing 

 stem, and horizontal when running across the direction of the stand- 

 ing stem. The mother-gallery may be either single- or double-armed, 

 and in working she makes one arm at a time. 



A more detailed consideration of the galleries or markings may now 



