INSECTS INJURIOUS TO CONIFERiE, 



6. The practice of growing large pure woods of Conifers of 

 uniform age tends especially to widespread ravages. Most 

 Conifer-feeding insects will not touch deciduous trees, and many 

 are confined to a single species of Conifer. Others, again, limit 

 their attacks almost completely to a single period in the life of a 

 tree. Curculio Ahietis is very destructive to trees under seven 

 years old, comparatively harmless to those of ten or more years. 

 In a pure wood the conditions favourable to increase of an 

 insect pest exist over the whole area at once, and there is no 

 limit to the supply of food, the facilities for egg-laying or for 

 migration to fresh districts from the part infected. 



Under the circumstances, a bad insect-attack localised in one 

 spot of an extensive forest is an exceedingly dangerous thing, 

 and it has been necessary on several occasions to isolate such an 

 area in a European forest and destroy it wdth fire to prevent 

 the hatching of myriads of wdnged moths which w^ould spread 

 over the neighbourhood. The danger and expense of so drastic 

 a measure are obvious. It is a universal rule that the larger 

 the district cultivated with any particular plant the greater is 

 the risk of insect-attack, while small isolated plantations become 

 infested with difficulty. A good instance is aiforded by the 

 annually recurring depredations in the Eastern Counties of the 

 Mustard-beetle (PhcBdon hetulcB), unrecorded as a destroyer 

 before 1854 ; with the continual growing of Mustard there the 

 insect flourishes, and will continue to do so till farmers agree to 

 rotate their crops, so that no Mustard shall be cultivated for a 

 year over large areas. 



Similarly the Easpberry-shoot borer {Lampronia ruhiella) 

 appears to be increasing in the South-east of England, owing to 

 the enormous Kaspberry-plantations which occur there. It is 

 not readily amenable to treatment, and is beginning to cause 

 annoyance to many growers. 



It will be convenient to take those insects now under con- 

 sideration in an order agreeing partly with the period in the life 

 of a tree when they are most mischievous, partly with the 

 character of the injuries they inflict, rather than in one deter- 

 mined by their zoological position. 



Seedling Conifers, if the nursery be placed in a well-chosen 

 situation, secure from the inroads of Curculio Abietis, are usually 



