298 MISC. PUBLICATION 657, U. S. DEPT. OF AGRICULTURE 
radiating mines. The cave burrow is the simplest and probably the 
most primitive type. Beetles making such burrows may be either 
monogamous, polygamous, or promiscuous. Examples of such insects 
are Cryphalus mainensis Blkin., Pityophthorus spp., and E’rineosinus 
sguamosus Blkm. 
(2) IrrecuLaR ELoncate Burrows.—In this type the entrance gal- 
lery is continued at the juncture of wood and bark for a variable 
distance, and then irregularly widened to provide a place for the 
deposit of eggs. The burrow ranges in length from several inches to 
a foot, or even several feet. The eggs are deposited i im masses in the 
wider areas on one or both sides of the main gallery and are protected 
by a wall of frass. This type of burrow is made by monogamous 
forms, such as Dendroctonus valens Lec. and D. terebrans (Oliv.). 
(3) Stmpre LoneGirupinat or TRANsvERSE Burrows.—These differ 
from the foregoing in that they are uniform in diameter throughout, 
and may be either longitudinal or transverse, straight or winding. 
Each burrow may or may not have a turning niche, or nuptial recess, 
at the juncture of entrance gallery and egg gallery. The eggs may 
be laid in egg niches arrang ed sy mmetrically or irregularly and there 
may be one or more egg grooves in which all the eggs are placed. 
The simplest burrows of this type, which contain no nuptial recess, are 
made by species of Scolytus and others. In Phloeosinus, Chramesus, 
and some other beetles the rather short galleries are similar, but each 
has a nuptial niche. In Dendroctonus frontalis Zimm. the burrows 
are much longer and are winding. Species making this type of 
burrow are monogamic. | 
(4) Forkep Lonerruprnat or Transverse Burrows.—In this type | 
the entrance gallery leads into a more or less enlarged chamber, from 
which the two egg galleries either extend in opposite directions or 
diverge at a very wide angle. Typical galleries of this type are those 
of species of Phthorophloeus, Hylurgopinus, and Leperisinus, which | 
are transverse in direction, and those of Scolytus piceae Sw., which | 
are longitudinal. Burrows of Cr yptocleptes dislocatus Blkm. are | 
also longitudinal but differ from the typical in that the eggs are not | 
placed in niches but packed in the sawdustlike frass in the main bore | 
of the gallery. In one species, Psendothysanoes drake’ Blkm., there | 
is a double-forked transverse burrow, appearing as if two forked | 
burrows were joined together by a short longitudinal gallery con- | 
necting with a common entrance. Beetles making the forked burrows 
are usually bigamous, but some are monogamous. 
(5) Raprare or Srar-SuHapep Burrows. In the radiate burrows the 
entrance gallery leads directly into an irregular chamber, known as 
the nuptial chamber, from which radiate the egg galleries, each made 
by a separate female. The egg galleries may be symmetrically ar- 
ranged as in those made by Pityogenes spp., Zps pini Say and some spe- 
cies of Pityophthorus, they may be chiefly longitudinal, as those by /ps 
calligraphus Germ. ; principally transverse as those by Pityophthorus 
liquidambarus Blkm.; or they may be irregular, as in Dryocoetes 
betulae Hopk. Radiate burrows are inhabited exclusively by polyga- 
mous forms. 
(6) Pira Burrows.—Several bark beetles such as Micracis opaci- 
collis Lee., Pityophthorus pulicarius Zimm., and several species of 
Myeloborus bore through the bark and wood and construct one or more 
ee UU” 
