ARBELA TETRAONIS. 441 
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the internal chamber remains uniform in width throughout its 
length. When full fed the larva bores straight into the wood 
of the tree, generally retiring to the middle of its covered 
way before commencing to bore in. From the observations 
I have been able to make on attacked trees I have little 
doubt that the caterpillar only enters the wood to pupate, and 
does all its feeding upon the bark. The tunnel in the wood 
is always straight, and does not ramify as it would do if the 
grub were feeding in the wood.* There is generally a raised 
lump on the covered way, the result of the addition of the wood 
excrement thrown out, marking the place where the caterpillar has 
gone into the wood (vdde fig. f). It enlarges the end of its 
gallery and changes to the pupal state. We do not yet know 
the time spent in this latter stage, but Mr. Fischer considers it 
to be from 3-4 weeks. In my description of the pupa I have 
shown that it is furnished with circular rows of spines; and by 
means of these, when the moth is ready to emerge, it wriggles 
and forces itself along the tunnel and pushes itself through the 
mass of excrement which forms the covered way, from which it 
remains protruding about a quarter of its length. After the 
moth has left the pupal case, the empty skin of the latter may 


*Inan article onthe “Casuarina bark-eating caterpillar (Avbela tetraonis),” 
published amongst the Scientific Papers inthe Indian Forester, XXXI, (1905) 
Mr. Fischer gives the following information upon this insect from observations 
published since the above was written :—‘‘ The earliest date upon which the larvee 
were observed was 26th August. They feed on the bark, restricting themselves 
to the superficial layers when very young and gradually working in deeper as 
they grow . . . Atanearly stage the larva constructs at one extremity 
of the covered way a small chamber under the bark, preferring to locate it in the 
upper angle formed by the junction of a twig with the bole. Here the grub 
rests when not feeding. It emerges to feed upon the bark immediately surround- 
ing the extremity of the ‘run’ which is built up further as the bark is eaten 
around it. It apparently feeds at night, as 1 have never found it by day outside 
the covered way, nor indeed anywhere but inthe chamber described. The larva 
attains its full size in March or April, and then prepares the pupal chamber. Up 
to this stage it has penetrated the bark alone except when an existing hole has 
been used asaresting chamber. If such a suitable hole has been found this is 
probably merely trimmed, otherwise the larva . . . bores into the wood and 
excavates a pupal chamber about an inch in depth, and this it enters in May or 
June, pupating with its head towards the orifice which is concealed by the 
extremity of the covered way.”’ 
H 
