1919] Blackman — Notes on Species of Pityophthorus 141 



insect's burrow, the beetle prevents the burrow from being flooded 

 by partially plugging the opening into the pitch-sinus with bits of 

 sawdustlike frass. The pitch-soaked frass is apparently used as 

 food and that eaten is replaced with new bits of "saw-dust." This 

 is continued until most of the more liquid pitch is drained from the 

 sinus and then the sawdust plug is eaten away and the burrow con- 

 tinued along the pitch cavity. The foregoing is based on direct 

 observation made with a binocular miscroscope. 



The beetles breed not only in the terminal twigs (Plate IX, fig. 

 4, b, c, d, e, f), but also in the larger twigs from 4 mm. to 8 mm. in 

 diameter (Plate IX, fig. 4, a) . They nearly invariably enter at the 

 axil of a smaller twig, constructing the nuptial chamber either on 

 the surface of the wood or in the inner bark, depending upon the 

 thickness of the latter. In the material at hand the egg-galleries 

 are short and irregular both in diameter and in direction. In 

 many cases the eggs are laid in piles or groups, and lie unprotected 

 in one corner of the nuptial chamber or in a wide alcove extending 

 from it. In still other instances the egg tunnels extend through 

 the axis of the twig in the pith and the larvae arising from the egg 

 niches in the walls of the tunnel bore directly through the soft sap- 

 wood to the inner bark surrounding it, where they continue their 

 burrows. The larval mines are broad and irregular and often 

 coalesce so that it is not unusual, on removing the outer bark of 

 larger twigs, to find a number of larvae working in a common cham- 

 ber excavated by their joint efforts. However, before pupating, 

 each larva in such instances, constructs a short individual burrow 

 ending in a pupation chamber. The larvse also seem to eat pitch, 

 as their burrows often involve pitch-sinuses and, indeed, individual 

 burrows frequently follow one of the pitch-sinuses for some distance. 



As regards the economic importance of P. puherulus, it will be 

 seen at once that insects which possess to such a marked degree the 

 ability to live in pitch, have the power to do considerable damage. 

 However, according to the writer's observations, these minute 

 beetles only occasionally attack perfectly healthy twigs. They 

 seem much to prefer the twigs of freshly broken limbs, or of limbs 

 which are undergoing suppression by shading, or which are un- 

 healthy from other causes. Apparently, then, they are only 

 occasionally injurious, and from the point of view of the forester, 

 are perhaps as often beneficial in hastening natural pruning, and 



