324 Studies in Forestry [CHAP. xiv. 



presence of more insectivorous birds than usual conveys a 

 plain hint to the thoughtful observer. Towards evening any 

 abnormal swarming of moths serves to put one on guard ; 

 whilst threatened large attacks of the Pine moth (Gastropacha 

 pint) may be foretold by the frequency with which the hiber- 

 nating caterpillars may be found under the layer of moss 

 covering the soil. 



Whenever thus forewarned, or when called upon to annihi- 

 late swarms of any injurious species that may have acquired 

 numerical strength enough to seriously threaten or interfere 

 with the vigorous growth and development of timber crops, 

 the exterminative methods adoptable vary according to the 

 habits of the insect occasioning the trouble and anxiety. 

 Some knowledge of its life-history is requisite in order that the 

 easiest point of attack against it on a large scale may be fixed 

 on. As, however, the methods usually adopted against beetles 

 differ essentially from those in use against moths, these two 

 great classes may be treated separately as forming two distinct 

 groups comprising the chief species of destructive insects. 



A. Annihilation of Beetles (Coleoptera). 



So far as many of the bark-beetles (Scolytidae) and weevils 

 (Curculionidae) are concerned, which chiefly breed in conifers, 

 the felling and barking of stems attacked, and the burning 

 of the bark whose cambial layer contains the ova, larvae, 

 pupae, and often imagines, are the first steps to be taken. 

 The foresters and woodmen should be carefully trained to find 

 out such infected stems, and should also be taught the 

 principle and the practice of felling a tree here and there so as 

 to form a decoy-stem, and thus prevent the beetles selecting 

 healthy stems for ovideposition in default of sickly ones. The 

 careful revision and subsequent burning of the bark must of 

 course be duly arranged for, and not on any pretence over- 

 looked. 



