COLEOPTERA. 



77 



As the larva? are always found on back-going or dead standing trees, 

 this species cannot be considered as directly injurious. It would 

 therefore appear, on first consideration, that the forest should not 

 only be kept free from dead trees, but also that all heavily suppressed 

 trees, showing distinct symptoms of death or premature decay, should 

 be cut. This principle, however, pushed too far, would not be in 

 keeping with first-class forestry, inasmuch as unbroken canopy must 

 be maintained throughout the period of growth, more especially in 

 youth and middle age, and dying or recently dead trees are quite 

 useful for estate purposes, provided proper creosoting be adopted. 

 Fig. 74 is from a photograph of cocoons on dead standing trees 

 underneath the bark. 



The life-history of the genus has been most carefully worked out 

 by Dr Stewart MacDougall, who 

 proved from both observation and 

 actual experiments that the dates 

 of appearance of perfect insects 

 were variable, as also the period 

 of time required for larval and 

 pupal duration itself. In North- 

 umberland the perfect beetles 

 emerge respectively most plenti- 

 fully about the middle of July. 



The female beetle lays her eggs 

 in the bark, and the larvae hatch 

 soon afterwards. At first the larvae 

 move from the egg -chamber in 

 different directions, forming a sort of star, but later on the markings 

 appear in long, broad, irregular lines, generally running lengthwise 

 with the stem. 



The larval markings are, as a rule, most conspicuous on the bark. 

 After the larva is fully fed it scoops out a chamber in the stem, and 

 covers itself over with the scooped-out chippings. Each larva makes 

 a chamber for itself, and those specimens which are fully fed in the 

 autumn pass the winter in the larval stage, pupate in the spring, and 

 appear as beetles during the summer. The chamber acts as a double 

 means of protection, inasmuch as it minimises the attacks of insect- 

 ivorous birds, and also shields the creature from injuries when the 

 loose bark is removed from the stem. 



Fig. 74. 



Cocoons of Pissodes pini on, stem of 

 Scots pine {reduced). 



