18 N. H. AGRI. EXPERIMENT STATION [Bulletin 247 



When several eggs were laid in a single leader within 24 hours, most 

 of the larvae hatched on the same day. Occasionally the eggs did not 

 all hatch on the same day and it was necessary to mark the unhatched 

 eggs by inserting in the leader a labelled pin close to the egg in question. 

 In some instances larvae hatching on different days were destroyed be- 

 cause of difficulty in following their subsequent movements in the leader. 



In Table II the gradual shortening of the egg stage as the season pro- 

 gressed is evident. In the insectary cage the maximum number of 15 

 days was recorded for eggs laid June 15. The maximum in the green- 

 house was 12 days for 11 eggs laid from June 14 to 16. Near the end 

 of the oviposition period a minimum number of 6 days was required in 

 the case of 8 eggs laid July 11 and 12. A minimum of five days was nec- 

 essary in the greenhouse for three eggs laid July 11. Earlier in the sea- 

 son, before tne observations were made that are included in Table II, it 

 was found that eggs laid May 19, 1927. required an incubation period of 

 20 days. The average length of the egg stage in the cage was 9.32 days; 

 in the greenhouse, 8.66 days. 



The averages for this and other stages have been determined by includ- 

 ing, first, separately, the data for each day in the cage and in the green- 

 house rearings. These daih- a^-erages were combined to get final figures. 



THE LARVAL STAGE 



The lar\-a, after eclosion from the egg, remains for several hours in the 

 pitch of the cavity. It then moves downward, feeding only on the cam- 

 bium and innermost bark while still very young. Later it consumes the 

 entire cortex, except the outer bark. When approaching maturity the 

 larva may also attack the outer wood parenchyma. The thin outer bark 

 remains intact forming a loose, brown jacket around the dead leader. 



Usually the larvae encircle the leader and work downward together un- 

 der the outer bark. This concentrated manner of attack is of advantage 

 to the larvae for the tissues are killed quickly and little resin is exuded. 

 If a larva feeds alone it seldom is able to survive the copious flow of re- 

 sin induced in a vigorous tree by feeding activities. 



The larvae progress rapidly down the leader. The route of descent can 

 easily be traced by the brown discoloration of the bark, which is evi- 

 dent soon after the larvae have fed on the underlying tissue. When 

 conditions are favorable and larvae are abundant they may work down 

 as far as the second or third whorl of lateral branches, a distance of three 

 or more feet. Often, however, they do not go below the first whorl of 

 lateral branches, a distance of eight to thirty or more inches. 



In general, from our observations, the average number of larvae in a 

 single leader varies from 30 to 40. However, a considerable percentage 

 of these fail to reach the pupal stage. July 17, 1928, one hundred sixty- 

 one larvae were noted in a single leader under cage conditions. One hun- 

 dred fort3'-four of the larvae were together in a band one inch wide 

 ;ii()und the leader near the base. Over 100 have often been found in 



