35 



Pinus strobus (white pine), P. resinosa (Canadian or red pine), 

 P. austriaca (Austrian pine), P. sylvestris (Scotch pine) and P. cembra 

 (Swiss pine). It is largely the cause of " spike-top " in mature timber 

 and stunts and kills outright innumerable trees of the so-called " second 

 growth." The timber of at least one area has been brought into such 

 ill-repute that carpenters and builders refuse to use it for any important 

 purpose. A systematic study of the life-history and habits of this 

 pest was undertaken in the autumn of 1912 and continued in 1913 

 and 1914. The particulars were collected only in Montana and Idaho, 

 but the moth is probably distributed throughout the United States. 

 The marked variations in colour of the caterpillars appear to be due 

 to the host flant. The chrysalis is without spines on tie segments, 

 which readily distinguishes it from an Aegeriid pupa that is frequently 

 found under somewhat similar conditions. The adults are chiefly on 

 the wing from 1st May to 15th September, but fertilised eggs are 

 deposited during any of the milder months and larvae of all sizes, 

 except the most minute in winter, may be found at any time of year. 

 Since no other pitch moth so seriously destructive to the trunks of 

 mature or nearly mature trees, leaves the entire pupal shell within 

 the bark or the pitch w^hich sheltered the immature insect, its identity 

 is quite easily determined. The eggs deposited in July appear to 

 hatch within about two weeks. In the latter part of August, the 

 mixture of coarse castings and brown bark dust which is thrown out 

 through the entrance and other holes in the bark indicates the presence 

 of the larva. Unlike the larva of the Aegeriid pitch moths, the cater- 

 pillar does not work into the cambium and stay there. After attaining 

 nearly half its full growth it usually leaves its hatching f lace and drills 

 again, often several feet away from the original spot. Migration is 

 not renewed in spring, each larva preparing for pupation in its own 

 individual tunnel by lining it with silken thread. Pupation takes place 

 about the middle of June. Eggs laid the previous autumn hatch in 

 early spring, the adults appearing during August and September of 

 the same year, while eggs laid in May yield adults early in the following 

 spring. In the northern Rocky Mountain region, Pissodes sclmvarzi, 

 Hopk., is a common associate of this moth in yellow pine, especially 

 when the trees are attacked near the base, as the work of this beetle 

 is rarely found more than 2 or 3 feet from the ground. The result of 

 infestation is identical. Aegeria (Sesia) brunneri, Busck, which is at 

 present known in Montana and Idaho, is also associated with 

 P. zimmermani in yellow and lodge pole pine. 



In Montana and Idaho, Pinipestis cambiicola, Dyar, is a most 

 important factor in regard to the existence of P. zimmermani. During 

 the latter part of June it infests the cambium of the terminal branches 

 of mature yellow pine, and many of these wounds are reinfested year 

 after year. Its work almost invariably causes .the knobby growth on 

 branches in w^iich P. zimmermani breeds undisturbed by woodpeckers, 

 and P. cambiicola must be therefore regarded as providing brood trees 

 for the more destructive insect. In most parts of the Rocky Mountains 

 Dryobates villosus monticola (Rocky Mountain hairy woodpecker) is 

 unquestionably the most efficient natural control of P. zimmermani . 

 Woodpeckers, however, never molest caterpillars under " spike-tops " 

 or in knobby branches on certain mature trees and this is evidently 

 the reason why their effects are so limited. The cocoon of an 



