12 



tunnels, their larvae cutting cradles similar to those excavated by larvae of the 

 Ambrosia beetles already mentioned, and are thus in a manner intermediate 

 in habit between Xyleborus and Trypodendron. The only Canadian species of 

 the genus lays its eggs free in the ends of the tunnels, and its larvae apparently 

 do not cut cradles.* 



The tunnels and cradles of Ambrosia beetles are lined with a fungus used 

 for food and usually characteristic of the beetle species, or at least of allied 

 groups of species. As this subject is to be discussed in greater detail elsewhere, 

 it is sufficient here to observe that all Ambrosia beetle tunnels are characterized 

 by the presence of one species of these fungi during the egg-laying season, and 

 later contain, in addition, numerous saprophytic as well as parasitic forms. 

 The tunnel walls are invariably stained brown or black by the action of the 

 Ambrosia fungus upon the wood. 



THE VENTILATION TUNNELS. 



These are short tunnels cut at intervals along the roof of elongate egg- 

 tunnels in certain species of Dendroctonus and Ips, directed outward towards 

 or to the outer surface of the bark (PL 2, fig. 3). The length of these venti- 

 lation tunnels depends upon the thickness of the bark overlying the egg-tunnel, 

 and may vary from a millimetre, or less, to more than an inch. They serve as 

 turning-niches and storage-places for boring-dust, and in some measure may 

 increase the air circulation within the egg-tunnels. Many such tunnels that 

 I have examined ended bluntly in the outer layers of bark, and could only serve 

 as turning-niches, storage-tunnels, and to increase the body of air available for 

 the beetles. With certain species, as Dendroctonus simplex Lee., the long egg- 

 tunnel is often blocked in places with boring-dust, so that these ventilation- 

 tunnels are perhaps useful, in such cases, for air circulation, but are certainly 

 necessary as turning niches for the female. 



*According to Chamberlain, Or. Ag. Exp. Sta. Bui. 147, 1918, the larvae of this species also cut cradles 

 shortly before pupating. 



PLATE 2. 

 TYPES OF EGG TUNNELS. 



Fig. 1, Forked, longitudinal. 



Fig. 2, Simple, longitudinal. 



Fig. 3, Radiate, typical. 



Fig. 4, Cave-tunnel. 



Fig. 5, Radiate, modified; Ips concinnus Mannh. a.h., entrance hole; e.p., egg-pocket; e.t. 



egg tunnel; l.g., larval gallery; n.c., nuptial chamber. 

 Fig. 6, Irregular, short. 

 Fig. 7, Radiate, transverse. 

 Fig. 8, Forked, transverse. 

 Fig. 9, Radiate, longitudinal. 



Fig. 10, Forked transverse, with larval mines, Phthorophloeus. 

 Fig. 11, Radiate, egg-tunnels commenced, Ips pini Say, from below. 

 Fig. 12, Ambrosia tunnels, simple, horizontal. 



Fig. 13, Ambrosia tunnels, compound, social gallery, X. saxesceni Ratz. 

 Fig. 14, Ambrosia tunnels, compound, with cradles, Pterocyclon mali Fitch. 

 Fig. 15, Pith tunnels, Micracis. 



Fig. 16, Ambrosia tunnels, compound, with cradles, Gnathotrichus . 

 Figs. 17, 18, Ambrosia tunnels, simple, vertically branched; Anisandrus. 



