May 2,1921 
Life History of Recurvaria milleri 
129 
appearance of the trees becomes apparent (PI. 30). It has been noted 
that this latter damage is most severe and conspicuous in mature or 
overmature stands, such as are found in the Tenaya and Cathedral 
Basins. There is a striking contrast in the degree of damage in different 
localities of the infested area. In the northern part of the Tuolumne 
Basin, in the vicinity of Kerrick Canyon, the damage is much less severe 
than in the Tenaya and Cathedral Basins, although the infestation has 
been present fully as long in the northern locality as in the southern. 
Dying tops and limbs would, of course, result from pathological condi¬ 
tions produced by other causes than the needle-miner. No disturbances 
aside from the needle-miner have been noted; but the pathological 
aspects of the problem have not been thoroughly studied. 
It has also been noted that the degree of damage varies greatly accord¬ 
ing to the site of the host tree. Trees standing on rocky, exposed sites, 
under unfavorable soil and moisture conditions, suffer much more severely 
than those standing on meadows where there is abundant soil and moisture. 
Much of the timber defoliated by the needle-miner has been attacked 
and killed by an entirely different insect, the mountain-pine beetle 
(Dendroctonus monticolae). No direct biological association, however, 
exists between the needle-miner and the barkbeetle, although the badly 
defoliated trees are apparently so weakened that they offer little, if 
any, resistance to the attacks of the beetles. 
Final and complete killing of the trees as a result of the needle-miner 
damage alone has not been recorded, although some of the more severely 
affected have reached a condition that offers little hope for their ultimate 
recovery. The insidious character of the needle-miner damage is not 
readily apparent in areas of recent invasion, but is very noticeable in 
stands where the infestation has persisted for a number of years. This 
will be readily understood by reference to the diagrams (fig. 1-3), 
which show that the attacks upon the needles occur in such manner as 
to allow the trees a breathing spell sufficient to maintain their vitality 
for a few years after the initial attacks. 
LIFE CYCLE 
The length of the life cycle is 25 months and covers a period of 1 year 
and parts of 2 other years. The individual broods hibernate during 
two winter periods of approximately 6 months each. The feeding periods 
of the larvae occur during parts of 3 years, aggregating a total period of 
11 months. Flight occurs every alternate year, as in 1913, 1915, 1917, 
and 1919. During the alternate years from flight the broods are found 
in the larval stage in the needles of the current or previous year’s growth. 
Emergence and flight of the adults occur during the period from July 
1 to August 31. For illustration of life cycle see figure 1. Some few 
individuals may be seen earlier or later than .these dates, but they repre¬ 
sent only advanced individuals and stragglers. During the period of 
