FOREST IMPORTANCE OF MYELOPHILUS MINOR HART. 
221 
a badly infested stem, irregular galleries are of frequent occurrence. A very interest- 
ing and puzzling form of mother gallery of M. piniperda may be found where the 
two species are breeding on the same stem. For example, in fig. 14 there is a 
mother gallery of M. piniperda loop- or inverted U-shaped. The female piniperda 
had made a gallery 2J inches in length, and, finding that she was about to cut 
across a gallery of M. minor , turned to the right, and continued the boring of the 
gallery vertically downwards. 
Length of Life-Cycle in a Single Generation. 
The number of days that it takes for the completion of a cycle from the laying 
of the egg to the issue of the young imago varies according to the season of the 
year at which the eggs are laid and the temperature, also on the quality of the 
food material and the position on the stem. Batzeburg and Hess, writing of Central 
Europe, give 75 to 84 days as the time in favourable environments, the times stated 
being — egg stage, 14 days; larva, 49 -to 56 days; pupa, 14 days. My observations 
at Aboyne in Aberdeenshire and my experiments in Edinburgh indicate rather a 
longer time. In January 1916 I found in the pine woods of the Aboyne district 
hundreds of adults of M. minor in young pine shoots lying on the ground. These 
shoots, tunnelled by the beetles, had been broken off from the trees by the winds, 
in the late part of December 1915. In sunny weather in April 1916 1 observed the 
beetles leaving these shoots and flying off to the young shoots in the trees above : 
into these young shoots the beetles bored to feed. The most careful search failed 
to reveal any minor boring into stems for brood purposes, although large numbers 
of M. piniperda had begun their brood galleries. 
On May 4, 1916, I found the first minor female commencing to bore an entrance 
and brood gallery for the purpose of egg-laying, and soon a male was found at the 
outside of the entrance-hole. Ten days later I dissected out this gallery, and found 
that it measured an inch in length and contained six eggs. Eggs hatched in times 
varying from 10 to 26 days. By May 15 numerous females had begun their mother 
galleries, and others continued to do so at intervals up to June 5. Females took a 
month to complete their two-armed gallery, and the first laid eggs had hatched 
before the gallery was completed and the last eggs laid. 
The larvae fed for 47 days and then pupated. The average time from the 
beginning of pupation to the exit of the imago in the latter part of August was 
30 days. 
From eggs laid at or about the end of May 1916 the first emergence of a new 
beetle was on August 25, 1916 — that is, in 95 days. The time taken from the entrance 
of a female underneath the bark, in making the mother gallery, in laying her eggs, 
and in the completion of larval and pupal stage to the exit of beetles, was 102 days. 
As exemplifying the effects which temperature and exposure have in hastening 
TRANS. ROY. SOC. EDIN., VOL. LII, PART I (NO. 10). 35 
