Il6 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



Trypodendron the whip of the antenna is four jointed, and the 

 club instead of being rounded is angular and is devoid of 

 sutures, being closely covered with hairs or bristles. 



In Tomicus and Pityogenes the whip of the antenna is five- 

 jointed, and the club is roundly oval. Three wavy rows of 

 bristles take the place of sutures. 



The difference between these two genera is, to the layman at 

 least, very slight. It lies in the underside of the pro-thorax, 

 called the pro-sternum, to which the first pair of legs are 

 attached. Between the coxae, or first joints of the legs, there is 

 in Tomicus a small but distinct angular process which is absent 

 in Pityogenes. 



The most common representative of the genus Tomicus is 

 T. acuminatus, while P. hidentatus is probably the commonest 

 Pityogenes. The two beetles are easily distinguished. In the 

 first place T. acuminatus is twice the size of P. bidentatus. It is 

 yellowish brown in colour. P. bidentatus is dark brown or black. 

 Further, the wing-covers in the two beetles differ very markedly. 

 In both they are scooped out at the apex, and the outer edges 

 are armed with short tooth-like projections. In the females 

 these teeth are less marked or absent as in P. bidentatus. 

 Tomicus acuminatus bears three short teeth on each wing-cover. 

 In the female all three teeth are simple. In the male the middle 

 tooth is double (Fig. 3^). In Pityogenes bidentatus each wing- 

 cover, in the male, bears a well-marked hook-like tooth. 



The above short descriptions may help the forester and others 

 interested to identify our commoner pine scolytids, but the 

 beetles may also be identified by the nature of their work. With 

 the exception of Trypodendron lineatum, all the beetles described 

 above are bark dwellers, breeding between the bark and the sap- 

 wood, where they construct their peculiar tunnels or brood 

 galleries. 



In the above description the genera Myelophilus and Hylastes 

 have been classed together, and again Totnicus and Pityogenes. 

 It is interesting that, if we except Myelophilus minor and base 

 our classification on the galleries, we get an exactly similar 

 grouping. Thus Myelophilus and Hylastes are both monogamous, 

 and both make simple vertical mother galleries, Tomicus and 

 Pityogenes, on the other hand, are both polygamous, and in 

 both genera the galleries consist of a central nuptial chamber 

 from which ramify three, four or five mother galleries (Fig. 9). 



