12 College of Forestry. 
controlled conditions were made in the laboratory, due to 
the fact that the size of the insect studied is so small that 
detailed observations were necessarily made at a consider- 
able magnification. 
The artificial cultures were made by placing freshly cut 
pieces of thin barked white pine hmbs in cylindrical glass 
jars. These pieces were taken from living white pine and 
were in most cases normal in every way. The glass jars 
were some of them closed with a loosely fitting glass cover, 
while others were closed with cheese cloth tied securely over 
the top. Into some of the jars limbs of pine known to be 
infested with P. hopkins: were introduced while into others 
were placed living adult beetles which had been removed 
from infested limbs. Thorough infestation of the new limbs 
oceurred in both, but the results were more prompt in the 
latter case. It was necessary to add water every few days 
in order to keep the pine limbs in condition to furnish suit- 
able food for the beetles and their developing brood. In the 
glass covered jars there was a decided tendency toward too 
great moisture which resulted in the development of fungi. 
In the cloth covered jars on the contrary the difficulty was 
in keeping the pine limbs in a moist enough condition. If 
a considerable amount of water was put in, the lower part 
the limb would absorb too much water while the upper part 
was too dry. best results were finally obtained by alternat- 
ing the two sorts of covers at intervals of several days. The 
occasional drying kept down the development of the fungi 
and also made conditions more like those occurring normally 
in nature where a dry period will alternate with a wet one. 
The cultures were quite successful and a larger percentage 
of the larvae reached maturity than in nature. One inter- 
esting reason for this is that the disproportion of the sexes 
as they occur in the brood burrows was not so great, doubt- 
less because the males were not subject to the dangers by 
which many lose their lives under natural conditions. The 
consequence was that each brood burrow contained the male 
and usually from one to three females while in nature the 
average number of females to the burrow is approximately 
