20 



niche, reversed her position, and advanced head foremost into the tunnel to 

 continue excavation and cover the egg with boring-dust. As the tunnel was 

 by this time covered with celluloid, she first proceeded to close the cracks between 

 it and the edges of the tunnel with boring-dust. 



REMOVING THE BORING-DUST. 



In removing the boring-dust, the female scrapes it backward with the 

 mandibles, which make a very efficient hoe. If she wishes to pack boring-dust 

 into egg-niches or to fill cracks in the tunnel wall, the dust is pushed forward 

 with the mandibles and packed by them into the proper position, but when 

 ejecting boring-dust from the tunnel it is always scraped backward, first with 

 the mandibles and then with the legs, working it beneath and behind the body. 

 By moving backward and at the same time revolving in the tunnel, the insect 

 is able to remove the dust without difficulty, and to eject it into the nuptial- 

 chamber, or to extrude it through the exit hole. . The tarsi are retracted more 

 or less, and the outer edge of the tibiae is used much in locomotion, and parti- 

 cularly in removing the boring-dust. The armature of the tibiae, of course, 

 assists considerably in both operations. 



A METHOD FOR STUDYING HABITS. 

 (PI. 4, fig. 6). 



In studying the habits of Ipidae, it becomes necessary to devise some method 

 of watching the beetles at work. All their operations, with the exception of 

 cutting the entrance-hole, are performed beneath the protecting cover of bark; 

 and when the latter is largely removed they invariably cease work almost 

 immediately and either leave the tunnels or retire to the uncovered portions. 

 If the tunnels, with the beetles in them, are covered in the proper way with 

 glass, celluloid, or mica, the excavation may be continued and much of the 

 work may be observed. We have secured best results with smaller species 

 working in thin bark, such as P. hopkinsi Sw., by removing the bark over the 

 nuptial-chamber and a part of an egg-tunnel, and immediately pinning thereover 



PLATE 5 

 BARK-BEETLE TUNNELS (ORIGINAL). 



Fig. 1, Pityokteines sparsus Lee.; egg-tunnels in balsam fir; wood surface; twice natural size. 



Fig. 2, Dendroctonus obesus Mannh.; tunnels in Sitka spruce bark; very much reduced. 



Fig. 3, Pityophthorus canadensis Sw.; Pupal cells in pine, showing larva and pupa in position; 

 about natural size. 



Fig. 4, Hylastinus obscurus Mannh.; tunnels in red clover roots, showing a beetle, and the eggs 

 in place in the niches; about natural size. 



Fig. 5, Phloeosinus canadensis Sw.; tunnels in arbor yitae, wood surface; two-thirds natural size. 



Fig. 6, Hylurgopinus rufipes Eichh.; tunnels in elm, inner surface of bark; about natural size. 



Fig. 7, Phthorophloeus liminaris Harr.; tunnels in peach limb, showing a portion of the brood; 

 one-half natural size. 



Fig. 8, Leperisinus aculeatus Say; tunnels in ash, showing the brood in position; about natural 

 size. 



Fig. 9, Pityophthorus nudus Sw. tunnel in pine, wood surface; twice natural size. 



Fig. 10, Pityophthorus canadensis Sw.; pupal cells in pine twig, showing full grown larvae and 

 pupae; natural size. 



Fig. 11, Phloeosinus canadensis Sw.; tunnels in arbor vitae, showing eggs in situ; one and one- 

 fourth natural size. 



