INSECTS. 



189 



9. Careful examination of the woods to see if injurious insects are 

 present (Fig. 36), and instructing the woodmen how to examine 

 decoy-stems left as traps for bark-beetles. 



Fig. 36. 



A sample-plot of Scots Pine ringed witli bands oj patent tar to ascertain if 

 the Nun -moth (Liparis monacha) is present (Saxony, 1900). 



Exterminative measures are needed when noxious insects are found to 

 be increasing, by such indications as bore-holes in the bark, bore-dust or 

 drops of resin, gnawed leaves, excrement, gradual thinning of the foliage 

 in tree-crowns, or the presence of insectivorous birds in larger numbers 

 than usual ; but these measures differ for beetles and for moths. 



(a) Extermination of Beetles. Many bark-beetles and weevils can be 

 destroyed by felling and barking Conifer trees attacked, and burning the 



