Hundreds of sticks of smooth bark trees of chestnut were examined
during the past winter and spring to determine the number and nature
of the larval exit holes of the bast miner. Every piece a foot long
and over two inches in diameter had bast miner burrows present. The
lowest number for a linear foot was one burrow while the highest was
fifteen. The number of exit holes for a small tree, therefore, would
vary from ten to one hundred and fifty. In one acre of chestnut trees
the number of these exit holes would be enormous. In the light of what
we now know, recent observations show that 50 per cent. of this class
of infections originated in bast miner exit holes.[8]
[8] Since writing the above, Prof. Ruggles has produced the mature
insect in breeding experiments and has thus completed our knowledge of
its life history, and finds the insect to be a species new to science.