May 2, 1921 
Life History of Recurvaria milleri 
133 
Activity is resumed in early May of the next spring, and the brood 
develops as larvae throughout the growing period of the second season. 
By the middle of July the larvae have mined two-thirds the length of 
the infested needles attacked during late summer of the previous year and 
are about half-grown, or nearly 4 mm. long. 
Beginning about August 5 of this season, or when the new needles of 
this year’s growth are nearly full-grown, the larvae begin to leave the 
mined needles in which the previous winter was passed and migrate to 
these new needles. The migration covers the period from August 5 to 
September 1, when practically all the brood is in the new needles (fig. 
2, 3). During this period the migrating larvae are exposed and may be 
seen crawling about on the needles and twigs. Undoubtedly a high mor¬ 
tality occurs during'the migration, but no statistics are available to show 
this. By the first of September the larvae are well established in the 
new needles of the current year’s growth which are attacked near the 
outer ends. These new and tender needles are mined very rapidly so 
that by September 15 one-half the length of each infested needle has been 
eaten. 
Toward the latter part of October and the arrival of winter conditions 
the brood again ceases feeding and becomes dormant, passing the second 
winter as nearly mature larvae in the first-attacked needles of the second 
season’s growth. 
Activity is again resumed the following spring in early May. During 
this spring-feeding period the larvae complete the mining of the needles 
in which the brood hibernated. These mined needles are then abandoned 
and the larvae attack green needles of the same growth, which by the 
last of May are from one-half to three-fourths mined; the larvae, now 
being full-grown, cease feeding and prepare the larval tunnels for pupa¬ 
tion in the needles mined last. These tunnels are slightly lined with 
silk and have emergence tubes leading to the covered exit holes near the 
tips of the needles. By the close of the second spring-feeding period 
each larva has mined an approximate average of two needles of the pre¬ 
ceding year’s growth. Thus, each larva mines three needles during its 
life cycle of 23 months—one during the first season of attack and one 
after each of the two migrations (fig. 2). From this it is obvious that of 
the crop of needles which develops after the season of initial attack twice 
as many needles are mined as of the crop which receives the initial attack. 
This accounts for the more conspicuous color phase and defoliation which 
are apparent every alternate year (PI. 29, D). 
Pupation begins about June 10 and is continued until August 5. 
Pupae form in the mined needles with the heads toward the tips. Emer¬ 
gence of the adults begins about July 1. Soon after the mined needles 
are abandoned by the migrating larvae or the emerging adults, the needles 
begin to fall from the trees (fig. 2, 3). 
36731°—21 - 2 
