136 PROTECTION OF WOODLANDS. 



The best annihilative measures consist in the laying down of 

 decoy-stems here and there (vide par. 61), and in duly peeling 

 and burning the bark from these after all the ova of one swarm- 

 ing-time have been deposited, but before any of the first beetles 

 have had time to make their exit. Burning of the bark is best, 

 though, where this is inconvenient, it is sufficient to expose it inside 

 upwards to the sun, if the brood is still in the larval stage. But 

 if the bark be thrown together in large heaps, as must occur when 

 the attacks of the insects are on any very large scale, burning is 

 absolutely necessary in order to destroy them. 



It is of particular importance that, in order to carry on 

 exterminative operations with fully successful results, another 

 supply of decoy-stems should be prepared against the second 

 time of swarming of the insects in summer, to induce them 

 to deposit the ova there. As a general rule, it may be said 

 that fresh decoy-stems should be felled every 4 to 5 weeks 

 throughout the summer and well into autumn, wherever 

 experience has shown that bark-beetles are likely to occur 

 in any large number. 



What has been said above concerning injuries inflicted, pro- 

 tective or preventive measures, and annihilative or exterminative 

 remedies, refers especially to the bark-boring beetles. The much 

 less numerous genera of wood-boring beetles, occurring in conifers 

 as well as broad-leaved trees (e.g., Oak), belong to the technically 

 injurious class of insects ; the trees attacked by these, especially 

 the broad-leaved species, often continue to live and flourish for 

 decades afterwards, although early utilisation of such stems is 

 certainly advisable in view of the constantly increasing deprecia- 

 tion in the value of the trees attacked. For such cases the fell- 

 ing of decoy-stems is of no avail, and other measures require to 

 be adopted in order to counteract the damage threatened, and 

 to reduce it to a minimum (vide par. 71). 



The bark-beetles are subdivided into three main groups, com- 

 prising about thirty species of sylvicultural importance : 



1. True Bark-beetles (Bostrichini) having the elytra often con- 



tracted and toothed at the lower end. They live chiefly on 

 conifers, but also on broad-leaved species, partly under 

 the bark and partly in the wood, but never breed in 

 the roots, like many Hylesinini. 



2. Cambial-beetles (Hylesinini) having the elytra or outer 



