144 



The Ottawa Naturalist 



[Jan. 



Ips balsameus Lee. Development of 

 larval gallery: 1, egg-niche; 2, egg- packing; 

 3, excrement of larva; e. t., egg-tunnel. 



Ips caelatus Eichk. Under side of 

 bark, showing the eggs in the pockets. , 



bark, forming irregular cavaties_ extending laterally from the 

 primary-tunnel. 



When the eggs are laid in niches the larva? burrow separately 

 through the bark or between the bark and the wood, at right 

 angles to the primary -tunnels ; these side tunnels, larval galleries, 

 or mines, thus formed increase in size as the larvae grow, and are 

 left completely filled with wood or bark fragments which have 

 passed through the body of the larvae. The latter feed entirely 

 upon bark or wood. 



If the direction first assumed by the larvae is not parallel 

 with the wood-fibres, the larval-mines are usually found to turn, 

 tending to follow the direction of the fibres. The larvae at and 

 near the ends of the primary -tunnel swing around almost 

 immediately, while those nearer the middle do so as rapidly as 

 is possible without encroaching upon the mines of their neigh- 

 bours. Usually the larvae keep carefully to their own preserves, 

 only crossing a neighbour's gallery when necessity compels them 

 to do so. When the larval mines are entirely in the bark their 

 direction has no definite relation to that of the wood fibres. 



After the larval development has been passed, varying in 

 length with the species, the ends of the larval mines are enlarged 

 and sometimes driven down into the wood to form the pupal 

 chamber. In some species the pupal period lasts but a week, 

 or ten days, in others the winter is passed in this condition. 

 After transformation is completed, the young adults cut their 

 way out through the bark, forming the openings known as 

 "shot -holes". 



While the primary-tunnel and also the egg-niches are 

 usually engraved in the wood, the larval-mines are often 

 entirely in the bark, or only cut the wood at the pupal-chambers. 

 On ash trunks, where the bark is thick, the larval-mines of 

 Hylesinus aculeatus but slightly engrave the wood surface, while 

 on small branches, where the bark is thin, the mines often cut 

 the wood as deeply as they do the bark. 



