PITH-RAY FLECKS IX WOOD. 7 



like a puncture of some sharp instrument. The coloration resulted 

 from the decay of the injured cells. Whether the larva first hatches 

 out of the egg outside the bark and then bores into the cambium, or 

 whether the adult female deposits the egg in the cambium itself, can 

 not be determined from the present investigation. 



Observations were next made about two weeks later — that is, about 

 May 10. The larvae had increased slightly m length, but scarcely at 

 all in diameter. Some had already reached the base of the tree and 

 started back, following for a short distance a path parallel to the old 

 mine, and then branching off obliquely (PI. II, fig. 2). Very few had 

 gone far do^^m into the roots at this time, but were burrowing in the 

 growing layer near the base of the tree. This was expected, since the 

 larvre were evidently guided in their movements by the food supply. 



During May there were examined specimens of black cherry, wild 

 plum, serviceberr}', red maple, and wild apple. From all of these 

 species larvae were secured similar to those already described. The 

 mines that were still free from wound tissue were readily followed as 

 the bark was removed. Often the larvge were secured by thus tracing 

 a mine to its termination. The number of larvae in each case varied 

 with the tree species and individual. In Maryland and Virginia 

 river birch appears to be the favorite host, mth wild plum, service- 

 berry, black cherry, red maple, wild apple, and silver maple follow- 

 ing in the order named. Certain specimens in a few localities were 

 almost free from larvae, while others seemed to be favorite hosts year 

 after year, as shown by the number of pith flecks in previous rings of 

 growth. 



During the period between May 25 and June 25 the larvae continued 

 to mine back and forth, seldom going more than 10 feet above the 

 groimd. As the larva grew larger the mmes gradually increased in 

 diameter up to several millimeters and often crossed one another. 

 The appearance of the wood was often misleading as to the nmnber 

 of larvae actually at work, since one larva, working up and down, 

 may make several flecks within the same annual ring. 



Pupation began about June 25. After this date the time of pupa- 

 tion seemed to depend somewhat on the age of the tree. In young 

 trees with relatively thin bark it occuiTed first, while larv^ were 

 secured from older trees with thick bark as late as Juh" 20. The 

 larvae proceeded down into the roots for varying distances. When 

 the roots are exposed, as along the banks of streams, the mines often 

 continue for a number of feet until they enter the ground. In trees 

 growing on flat land the roots are seldom penetrated for more than 

 3 feet. In such instances the larvae generally return to a position 

 near the base of the trunk and pass out tln*ough the cortex. 



Pupation takes place in the ground. The larvae bore a small hole 

 through the bark and come out in the earth. The end of a mine is 



