140 
Journal of Agricultural Research 
Vol. XXI, No. 3 
In 1919 the infested areas were determined as follows: South of the 
Tuolumne River in Tenaya and Cathedral Creek Basins, Snow Flat and 
Porcupine Flat, and Ten Mile Meadows; on the headwaters of the Tuo¬ 
lumne River throughout the Tuolumne Meadows as far east as Lambert 
Dome and the terminus of the Lyell Fork Canyon; down the Tuolumne 
River to and throughout Conness and Alkali Creek Basins and Glen 
Aulin. The infested areas north of the Tuolumne Canyon occur in the 
Matterhorn Canyon, around Benson Lake, and throughout the canyons 
of Kerrick, Stubblefield, and Jack Main. The range of the infestation 
covers an approximate total area of 60 square miles, or 39,000 acres. 
The records now available indicate an advance of the infestation 
toward the southwest. In 1906 no evidence of the needle-miner was 
found in Tenaya Basin or the Tuolumne Meadows. In 1911 the infesta¬ 
tion was prevalent and conspicuous in both these areas. In 1912 it had 
not advanced beyond the divide between Tenaya and Snow Flat, but in 
1917 infestation was very heavy throughout this latter area, and in 1919 
it was conspicuous in Porcupine Flat still farther southwest. The 
limits of the host type are reached in Porcupine Flat, so that further 
advance to the west will necessitate a migration of 6 miles over a high 
ridge to the lodgepole pine stands in Yosemite Creek Basin. 
Records show that the invasion of a new area occurs suddenly, the in¬ 
festation reaching an epidemic condition in one year, with resultant very 
heavy defoliation from its inception. 
Old centers of infestation are indicated in the stands in Jack Main and 
Matterhorn Canyons. The greater portion of these stands is now dead, 
having been killed by the mountain-pine beetle years ago, but all indica¬ 
tions point to the fact that the needle-miner was present in these areas 
prior to the advent of the beetle. The needle-miner is still present in 
both these canyons, infesting the remaining trees. 
In Virginia Canyon, north of the Tuolumne Meadows, the needle-miner 
was present in 1911, as shown by the mined needles found under the trees 
in 1913 and the absence from the twigs of a heavy percentage of the 
1910 needle growth; but for some reason that has not been determined 
the moths abandoned the area in that year, and no trace of existing 
infestation has since been found. This is the only area now free of in¬ 
festation in which previous infestation has been known to exist. 
Heavy stands of lodgepole pine occur in the Illilouette Basin and in 
other areas south of the Merced Canyon. These are the only large 
stands of lodgepole pine left within the park that have not been invaded 
by the needle-miner, although they are situated in the same zones of ele¬ 
vation as are the heavily infested areas around Tenaya. Invasion of 
these stands by the needle-miner may occur at any time; in fact, the in¬ 
festation is drifting in this direction, as is indicated by a small area of 
infestation which appeared in 1919 on the slopes of Clouds Rest just 
across the Merced River from the Illilouette Basin. 
