Jan. IS. IP'S Agrihis Bilineatus 291 



XXXIX, figure 3, shows, the transverse direction is the usual one in the 

 last instar, especially when the bark is thick, while during the earlier 

 instars the burrows run in a more oblique direction. 



No evidence can be offered as to the duration of instars. Larvae which 

 were in the first stage were found from July 21 to August 13, mature 

 larvae were found in their pupal cells as early as August 7, while the 

 intermediate stages were found throughout this period. 



It was found that the lar\'ae in the last instar burrow from 2 or 3 to 

 23 mm. in 24 hours. Larvae of the second instar burrow as far as 6 mm. 

 in the same length of time. Upon consideration of these records it is 

 not surprising that trees infested with Agrihis hilineatus appear to die 

 suddenly when larvae are to be found as numerous as shown by the 

 burrows in Plate XXXIX, figure 3, where each one may consume cam- 

 bium tissue equal to nearly twice its own bulk every 24 hours. In the 

 section shown there were nine larvae in approximately i square foot of 

 bark, each burrowing across the cambium layer. It was also found that 

 when the larvae are so numerous that they confront each other, one or 

 the other is eaten through as if it were merely cambium tissue. This 

 may become an important economic factor, for cases have been obser^'ed 

 in bark which was crowded with grabs where a number of dead lan-ae 

 were found with burrows passing through their abdomens or even their 

 heads. 



The slowest burrowing was found to be -in the dry wood, where the 

 tissue was evidently the toughest and of the least nutritive value. Trees 

 with growing tissue offer the best opportunity for making extended 

 burrows with great nutritive value to the lar\'3e and to the detriment of 

 the tree. On the other hand, as soon as the tree dies from being girdled, 

 the tissue becomes dry and offers more resistance to the burrowing and 

 is of little nutritive value to the larvae, which may die. A tree which 

 was grubbed up on July 30, at which time it had just died, was examined 

 on August 13. The dried bark, especially on the side exposed to the sun, 

 contained shriveled larvae, over 50 per cent of which were dead. Similar 

 conditions were found in other trees that had died early in the season, 

 when the dryness seemed to affect the larvae more than later when they 

 are in the pupal cells. This may also explain the condition described by 

 Chittenden, who stated that burrows were found in trees, but no lar^-«E 

 were present.' 



In summarizing the work of the larvae of the two-lined chestnut borer 

 it is also of economic interest to note the wide distribution of the bur- 

 rows on the tree, from the small branches less than an inch in diameter 

 and between 40 and 50 feet from the ground down even to the roots, 

 where in one case a larva was found constmcting a pupal cell 1 1 inches 

 below the surface of the ground. 



' Chittenden, F. H. I.oc. cit. 



