AND OTHER INSECTS WHICH INFEST CONIFERS. 125 



twigs and branches from early prunings or thinnings. It has 

 been frequently observed that they prefer locating themselves 

 among these cut branches to any other shelter or cover, so long as 

 they find them in a fresh, although drying, condition ; and they 

 will invariably settle on them rather than on any part of the 

 growing trees themselves. This predilection for shoots in a semi- 

 dry or half-withered state is further attested by the circumstance, 

 that insects which attack the fir tribe invariably commence upon a 

 subject already evincing indications of sickness or decay. This 

 is apparent in woods where no pruning or thinning has afforded 

 them an opportunity of selecting their favourite haunts among 

 felled branches and stools, and in the absence of such they are 

 universally found to select apparently sickly specimens in preference 

 to very robust and healthy plants, the juices of luxuriant and 

 vigorous growths being probably too strong and rank in their 

 vitality for their slower insect development and economy. 



One explanation of this generally observed preference of insects 

 of various orders for diseased or sickly specimens of the trees 

 they prey upon, is given by M. Audouin, Professor of Entomology 

 in the Museum d'Histoire Naturelle at Paris, who has closely 

 studied and noted the habits of many insects, and there appears to 

 be good ground for accepting it as authentic and reliable. He 

 thinks that the quasi-incipient decay of the tree is due, not to 

 any inherent failure in the plant-life of the specimen, but to the 

 attacks and boring operations in the bark of the tree caused by 

 the search of the male insects (chiefly) for food, which injures the 

 bark, inducing an unhealthy foliage ; into these subcortical bor- 

 ings the female deposits her eggs; and so what we usually ascribe 

 as the primary cause of the tree's sickness is merely the secondary 

 result of the creature's operations, which are really an attack, in the 

 first instance, upon a healthy tree for food. These borings weaken 

 and exhaust the functions of the bark, whereupon the female 

 deposits her eggs in the previously made workings of the male 

 insect, whdo the act of burrowing and depositing the eggs and of 

 so injuring the tree are commonly supposed to be confined only to 

 trees which previously evinced signs of decay. In the Eeview 

 Entom. (iv. p. 115), Sdbermann also states, upon the authority of 

 Dr Eatzeburg, that the large weevd (Pissodes notatus) attacks the 

 bark of young pines with its trunk, and thus renders the trees un- 

 healthy, prior to the female depositing her eggs in them. 



The modes of insect attacks upon coniferous trees may be directed 



