The Spruce Budworm 



425 



buds, where they feed on the tender 

 young needles which are just starting 

 growth. They also feed on spruce and 

 fir pollen. As the new shoots elongate, 

 the larvae tie the needles together with 

 silken threads and thus form shelters 

 within which they feed. By late June 

 they are full-grown, reddish brown in 

 color, and start forming the pupal 

 cases, which are attached to the twigs. 

 The pupal period lasts 7 to 10 days, 

 after which the moths emerge and start 

 laying eggs a new generation is under 

 way. 



The spruce budworm may spread 

 over long distances to new areas by 

 flights of the moths. Records of the 

 1910-19 outbreak show that in July 

 1911 swarms of moths appeared in 

 Philadelphia and in 1912 and 1913 

 they were abundant in Connecticut. 

 Those localities are outside the general 

 spruce-fir range, so the presence of the 

 moths there had significance only in 

 showing how far they travel. 



The regions where extensive tree 

 mortality has already occurred in the 

 present outbreak and the extent of the 

 active infestations are shown on the 

 accompanying map. There is no record 

 of a flight of moths in 1944 from Can- 

 ada that might have caused the out- 

 break conditions discovered in New 

 York in 1945. Apparently, though, a 

 heavy infestation arose simultaneously 

 over an area of approximately 3,000 

 square miles, and careful study of the 

 area in 1945 pointed strongly to the 

 possibility of a widespread flight of 

 moths in 1944. 



DURING AN OUTBREAK PERIOD, a 

 heavily infested tree may harbor thou- 

 sands of caterpillars. Except when the 

 young caterpillars first resume activity 

 in the spring and form mines in the 

 old needles, the new foliage is the pre- 

 ferred food and it is entirely devoured 

 before the old foliage is eaten. 



In heavy infestations the trees first 

 exhibit a scorched appearance. Later 

 they turn grayish as the foliage disap- 

 pears. Finally dead tops become evi- 

 dent. A heavy defoliation for several 



years will reduce the volume of foliage 

 to a degree where many of the cater- 

 pillars die from starvation and the bud- 

 worm population declines, but in the 

 meantime many of the trees will have 

 died. Following the decline of the in- 

 sect in a particular area, the loss of 

 trees continues for several years, be- 

 cause secondary insects and fungi have 

 a part in killing weakened trees. 



The feeding habits of the spruce 

 budworm determine to a large measure 

 the damage in various types of stands. 



The caterpillars show a definite pref- 

 erence for fir in that they develop 

 readily on both old and current growth. 

 Although the budworm feeds readily 

 and develops rapidly on pollen from 

 fir trees, the presence or absence of 

 abundant staminate flowers has little 

 effect on the budworm population in 

 the forest. The lack of synchronism be- 

 tween budworm development and 

 opening of buds and the poor survival 

 on old foliage of red and black spruce 

 indicate that these two species are less 

 favorable food plants than balsam fir. 

 This fundamental information on the 

 biology and feeding habits of the spruce 

 budworm and the fact that mortality 

 in all species of attacked trees is directly 

 proportional to the lack of vigor at the 

 time of defoliation give us a basis for 

 formulating methods for the silvicul- 

 tural control of this insect. 



Investigations made during and 

 after the disastrous outbreak of 1910- 

 19 in New Brunswick and Maine in- 

 dicated that the greatest mortality of 

 trees occurred in the red spruce-balsam 

 fir type, particularly where the fir pre- 

 dominated and was overmature. 



Little damage occurred in the mixed 

 hardwood-spruce fir stands, where the 

 hardwoods overtopped the conifers. 



White and black spruce appeared to 

 suffer less from attack than red spruce 

 and fir. 



THE RESULTS of the earlier studies 

 and the intensive work of Canadian 

 and American entomologists during 

 the present outbreak point the way 

 toward a possible solution. 



