THE ENEMIES OF ENGLISH WOODLANDS 273 



INSECTS. 



The insects injurious to trees at one period or another of 

 their existence may be divided into two classes those which 

 attack healthy individuals, and those which confine themselves, 

 under ordinary circumstances, to sickly or unhealthy specimens. 

 In dealing with the former class, war must be waged against 

 the insects direct, either as larva, pupa, or imago ; but, in the 

 case of the latter, attention to the health of the trees by 

 planting them on suitable soils, or by attending to cultural 

 details, is the most effectual means of preventing attack 



The insects which have any practical significance as being 

 injurious to healthy trees are chiefly found amongst the 

 Lepidoptera, Coleoptera, and Homoptera. They include the oak- 

 leaf roller moth (Tortrix viridana), the winter moth 

 (Clieimatobia Irumata), the larch aphis (Chermes laricis), the 

 pine beetle (Hylurgus pinniperda), the pine weevil (Hylobius 

 abietis), the cockchafer (Melolontlia vulgaris and Hippocas- 

 tance), and the garden chafer (PhyllopertJia horticola). 



This list might be extended until further orders, but it is 

 only intended to deal with those which may now and again 

 prove themselves to be dangerous pests to healthy timber 

 trees in woods and plantations. Hundreds of insects attack 

 trees more or less every season, but the majority of such 

 attacks do not permanently injure the trees, or appreciably 

 reduce their production of timber, and consequently they do 

 not bring themselves within the range of practical forestry. 

 The average forester has usually more than enough to do to 

 cope with the ordinary routine of estate wood-work, and has 

 rarely time to undertake any but urgent measures of insect 

 prevention. Fortunately for him, some of the worst forest 

 pests are unknown in this country, or only known as 

 entomological curiosities. Black-arches moths, fir-spinners, 

 and others, which destroy thousands of acres of pine forests 

 in one season in the north of Europe, do not jeopardise the 

 existence of British woodlands at periodic intervals. Even 

 our worst pests are sufficiently harmless, and few in numbers, 

 to escape notice in an ordinary season, and it is only 

 at rare intervals that a really serious visitation occurs, 

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