History and Habits of Pityogenes. 45 
that temperature also aids in determining the length of time 
the adults remain in their larval host. If they reach adult 
condition in the fall they do not emerge from their feeding 
burrows until the following spring. As has already been 
stated, the time of emergence also varies with the sex, the 
males .seeking a new host several days in advance of the 
females. 
Proportions oF THE Syxes.— The two sexes as repre- 
sented in the feeding burrows before any have emerged, occur 
in equal numbers, as has been determined by careful counts. 
Yet as the sexes exist in the brood-burrows there is a great 
preponderance of females as Pityogenes exhibits the poly- 
gamous habit to at least as marked a degree as any other 
genus of bark beetles (Figs. 26, 27, 28). Actual count of 
sixty brood-burrows occurring in nature, showed according to 
the engravings, that the parent females outnumbered the par- 
ent males in the proportion of 2.83 to 1. Of these sixty bur- 
rows only six contained a single egg gallery, seventeen had 
two, twenty-two had three, twelve had four, two had five and 
one had six egg galleries. Other brood-burrows of this same 
species have been observed which possessed as many as eight 
egg galleries. 
This disproportion of the two sexes in the brood bur- 
rows may be explained by two factors. A number of males 
were found both in the laboratory cultures and in nature, 
which had completed their nuptial chambers and had 
evidently lived in them and fed in them for a number of 
days, but had not succeeded in attracting any females, al- 
though other burrows within an inch or two contained from 
two to five. In the material started in the laboratory, several 
males were still alone in their burrows, while other burrows 
in the same bit of wood which were started on the same day, 
contained nearly full grown larvae. There can be little doubt 
that these individuals would die bachelors, although both they 
themselves and their burrows seemed to conform to the same 
specifications as others which were occupied by growing fam- 
ilies. But the factor which seems most important in determ- 
ining the disproportion of the two sexes in the brood bur- 
rows is the greater danger to which the male is exposed be- 
