ay 
, 
' 
66 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
the end of March and the beginning of April, and after pairing, 
the female, under cover of the bark scales, begins to excavate her 
tunnel in some sickly standing pine, or in a stump, or in felled or 
fallen timber—preferably of the genus Pinus. As a rule, the place 
chosen has thick bark, although I have repeatedly found the 
tunnels where the bark was quite thin. The tunnel crooked to 
begin with, but throughout the greater part of its length vertical 
(Somerville has well compared its shape to a golf-club), is com- 
pleted in from four to five weeks, and along its sides, in little 
excavated niches, the hundred or more eggs are laid. The tunnels 
average 3 to 4 inches, although they are often longer, one I cut 
from a tree two summers ago having a length of 114 inches. From 
the eggs hatch out grubs, which begin to gnaw tunnels in the 
cambial region. These grub-tunnels are at right angles to the 
mother-tunnel, and ultimately become winding, increasing in size 
with the growth of the larve. When full-fed, each grub pupates 
(passes into a resting stage) in a little cell formed in the bark at 
the end of its tunnel. The perfect beetles appear in June and 
July, according to the order of egg-laying, in some seventy-five to 
eighty-five days from the laying of the eggs. The earliest issuing 
beetles start breeding at once, with the result that a second brood 
of beetles appears in September. In unfavourable weather condi- 
tions there may be only one brood in a year, but with the weather 
conditions favourable, Somerville has proved beyond dispute that 
in Scotland two generations appear in the year. 
Taking the favourable weather conditions, the following may 
stand as the Calendar for the Pine Beetle :— 
| 
Noy. 1895-| End of | April and | 
March1896.| March. May. June. | July. August. September| October. 
eras aaa =a ome emer | 
Beetlesin| Beetle | Larve. | Pupa Eggs. | Larve. | Larve. | Beetles. | 
winter jand eggs. Beetle. | Larve. | Pupa | 
quarters. | | Beetle. | 
The second generation of beetles, which emerges in September 
and October by boring their way through the bark from their pupal 
cell (the flight-holes giving the bark an appearance as if riddled 
with small shot), make their way to the young shoots of the pine, 
and bore into these—not for egg-laying, but for feeding purposes— 
a little ring of resin marking the entrance hole. These bored 
shoots can be found in large quantities below the trees after a gale. 
Repeated attacks of the Pine Beetles, and loss of these shoots, soon 
