278 ENGLISH ESTATE FORESTRY 



easy and effectual methods of prevention. Fortunately, no 

 insect pests can be dealt with so readily as the pine beetle, 

 provided the area it frequents is placed under uniform 

 treatment at one and the same time. It is little use for 

 the one forester or proprietor to put preventive methods 

 into force, while his neighbour over the way or over the 

 ditch, as the case may be, allows things to take their chance. 

 Where large numbers of pine beetles have managed to 

 hibernate or breed on an area of, say, one square mile, 

 preventive methods must be exercised in places liable to 

 attack over the whole of that area, if the foe is to be 

 successfully fought. What form these measures should take 

 depends upon circumstances. The most frequent cause of 

 large numbers of beetles existing on a definite area is usually 

 the leaving about of fallen or blown timber in the woods 

 through the summer. In such cases, not only does every 

 pair of beetles which has hibernated find feeding and 

 suitable breeding material in this timber, but the eggs laid 

 by each pair develop into a new and much more numerous 

 generation in a couple of months. This means that each pair 

 of beetles at the beginning of a season is multiplied into at 

 least fifty pairs by the middle of it, and these fifty pairs are 

 again multiplied by fifty if a third generation is able to de- 

 velop. It is easily seen, then, that a month or two's neglect 

 may bring about enormous swarms of beetles, which, sooner 

 or later, will continue their existence in the crowns of grow- 

 ing pine trees within a certain radius. The extent of damage 

 done in such cases varies, of course, with the age of the trees 

 attacked. The loss of a few shoots in an old pine tree which 

 has finished its growth is not a serious matter, as the loss of 

 a comparatively small number makes no appreciable differ- 

 ence to the production of wood ; but, in the case of young or 

 middle-aged trees which are still adding to the growth of 

 their leading shoots, the loss of the latter may seriously 

 affect the ultimate yield of the plantation, and also produce 

 crooked stems which depreciate the value of the trees. 



The importance of preventive measures becomes all the 

 greater, therefore, the larger the area of young pine trees hap- 

 pens to be. Where nothing but mature timber is present, 

 the economic significance of the beetle is not great, as the death 



