130 PROTECTION OF WOODLANDS. 



3. Boot-destroyers, including the caterpillars of the Seed Owlet- 



moth (Agrotis), the grubs of the cockchafer, and the 

 mole-cricket (Gryllotalpa vulgaris). 



4. Bud-destroyers, including a number of Tortricidx and Cur- 



culionidte. 



5. Mast or Seed destroyers, as for instance the Acorn-borer 



(Balaninus) and the Spruce Cone-twister (Grapholitha 

 strdbilella). 



6. Producers of Deformities or Malformation, including Gall- 



wasps (Cynipidie), Gall-midges (Cecidomyidse), Plant-lice 



(Aphidie), &c. 



Insects are also classified as physiologically or technic!/t/ 

 injurious according to the injuries inflicted. These may on the one 

 hand occur on important organs, and disturb the plants in their 

 growth, or even cause their death ; and on the other hand they mi y 

 be connected with the riddling of the stems with holes, whereby 

 the timber is rendered, to a greater or less extent, useless for 

 technical purposes. Those comprised among the former are by 

 far the more numerous, including all such as destroy the cambial 

 layer, foliage, buds, and roots ; whilst among the latter class are 

 included the genera already named as timber-destroying insects 

 (some Scolytidte, Ccrambycidie, Siricidse). 



According to the age of the timber crops which are most 

 liable to their attacks, insects may be either classed as destroyers 

 of young plantations and seedling growths, or else as, for the 

 most part, and sometimes exclusively, enemies of crops which 

 have already passed through the sapling and thicket stages of 

 development, and have entered upon the pole-forest or the tree- 

 forest stage of growth. Amongst the former are found most of 

 the Curculionidfe, some Tortricidte, and the grubs of the cock- 

 chafer (MdolontluC) genus of the Scarabmdx ; whilst the latter 

 include the majority of the Lepidoptera, although many species at 

 first exhibit a decided amount of choice between pole-forests and ? 

 tree-forests when they commence their destructive operations. 

 Thus, for example, experience shows that the Pine Span-worm or 

 Bordered White Moth (Fidonia piniaria), and the Pine Owlet-moth J 

 or Pine Beauty (TracJiea piniperda), always attack pole-forest first, 

 and then only later migrate to tree-forest if their numbers be 

 allowed to increase ; whilst the reverse holds good regarding t 

 Pine Moth (Gastropacha pini), and the Black Arches, " Nun," 



