4 BULLETIN 255, U. S. DEPARTMENT OF AGRICULTURE. 



degree until pupation, which takes place in the third season after the 

 deposition of the egg. 



The head is small and rounded ; the body cylindrical, rather slender 

 in comparison with that of the larvae of other sesiids. When full 

 grown it is from 1 to 1^ inches long. 



THE PUPA. 



The pupa is shining brown, armed with transverse rows of spines 

 on the back of the abdominal segments, by aid of which it moves 

 back and forth at will in the tunnel made by the larva before pupa- 

 tion in the covering pitch mass. When ready for the final trans- 

 formation the pupa uses these spines for working its way through 

 the thin layer of pitch at the mouth of the tunnel, by projecting its 

 anterior segments to at least one-half of the entire pupal length 

 through the opening, and holding itself securely during the escape 

 of the moth. 



SEASONAL HISTORY. 



The pupal period as observed in the laboratory is 30 days, but 

 under adverse weather conditions it seems to be prolonged a few 

 days. Usually moths appear in greatest numbers the first sunny 

 day after a rainy spell. 



The general emergence of the Douglas fir pitch moth occurs dur- 

 ing the month of June, although individuals emerge in Montana as 

 early as May 15, and farther west adults may be found by the first of 

 that month. On May 20 the writer noted the first female (no male 

 was observed at large during two years of observation) flying up 

 and down a Douglas fir tree, evidently in the endeavor to locate a 

 favorable spot for oviposition. Fresh empty pupal shells were 

 observed protruding from pitch tubes on infested trees as early as 

 May 15. A living chrysalis was found early in April, which, 

 allowing 30 clays for pupation, would evidently result in adults 

 appearing early in May. It is- rather striking that most of the 

 early chrysalids were found at the highest altitudes in which the 

 moth is active. This makes it probable that the shortened seasons 

 at high altitudes are frequently responsible for an extension of the 

 larval period into the fourth year, just as, in consequence of late 

 August oviposition at lower altitudes, a certain percentage of the 

 insects do not attain maturity during the three years that this species 

 requires for development from egg to adult. In such instances the 

 larva pupates during the first warm days of the fourth season. 

 Occasionally adults emerge up to the last of July and the first part 

 of August. 



The mature insect lives only about five days after emerging from 

 the pupa, which accounts for its scarcitv- Even where its work 



