FOREST INSECTS ON THE CULBIN SANDS. I39 



the well-known German forester, pointed this out many years 

 ago ; but in this country, and even in Germany, Hylobius has 

 been too much associated with the felled area, and its mode 

 of living under natural forest conditions rarely considered. So 

 it is with the majority of our forest pests. They are always 

 present in our woods ready to take advantage of any conditions 

 favourable to them in order to extend their range. If the 

 conditions do not favour them they may lie dormant, as it were, 

 for years, appearing apparently without cause and without warn- 

 ing in large numbers, as the Larch Sawfly did some years ago in 

 the Lake District. The most remarkable recent instance of the 

 rapid increase in numbers and range of a forest insect in 

 Britain is afforded by the Black Pine Longicorn beetle, Asemum 

 striatum. For many years before the war this beetle was 

 considered rare, even by coleopterists who knew something 

 of its habits. As a result of the war-fellings it is now one 

 of the commonest of our longicorns, and the curious oval exit 

 holes which it makes on the cut surface of pine stumps are 

 probably familiar to most observers. The case of Asemum 

 striatum is doubly interesting, first because of the rapid increase 

 in its numbers, and secondly, because its characteristic exit 

 holes afford a ready means not only of determining its mere 

 presence in a district, but also afford a means of tracing its 

 rate of spread and increase by comparison of areas felled 

 prior to the war and after it. This beetle in the years before 

 the war held its own in the struggle for existence ; the war- 

 fellings shifted the balance in its favour, and it rapidly increased. 

 To-day it is probably again on the decline. So it is with all 

 our forest insects, and a study of the conditions or factors 

 which favour and retard them respectively, is one of the most 

 important branches of forest protection. It is this branch of 

 forest protection that is most likely to prove useful on the 

 Culbin Sands. The young plantations now being formed there 

 must be protected from the surplus insect population of -the 

 Low Wood. That they may be invaded by that population two 

 interesting observations show. On loth May, on the blown 

 and as yet unfixed sand about a mile east from the borders 

 of the Low Wood, nine Hylastes ater were found alighting and 

 crawling on the sand, and Mr Annand, the Divisional Officer 

 for the North-East of Scotland, found, as he informed me, an 

 adult Hylobius near the same spot in July. 



