124 
off. In one instance, followed in the insectary from the 12th of 
July, 1905, to the 12th of the following June, a larva thus ampu- 
tated eight lateral twigs. 
The cavity made in the twig, although apparently a close fit for 
the larva, is nevertheless large enough to permit it to turn upon it- 
self and to move in either direction. Of twenty-three larv?e exam- 
ined May 22, eleven were lying with heads towards the tip of the 
twig and twelve towards the hase. It frequently happens, where a 
tree is as heavily infested as were many of those in Decatur, that 
eggs will be laid in several small spurs all leading to a larger twig in 
wdiich all the larvse which li\-e must finally meet. A destructive 
competition must follow, since each infested twig harbors, finally, 
only a single surviving borer. 
When a larva passes down a smaller twig to a larger branch, it 
burrows only in the newer wood immediately beneath the bark. In 
such a branch it commonly takes a winding course, its track in one 
instance even doubling back upon itself for a considerable distance. 
The larvae, in various stages of growth, hibernate in their bur- 
rows and finish their growth the following spring. May 22, for 
example, they were found by Air. Webster in the wood of the pre- 
ceding year, still burrowing downwards, with the effect to kill the 
lateral shoots as they passed. 
Pupation occurs within the burrow, in a cavity shut oft' in both 
directions by a firm plug of mingled woody fiber and excrement. 
The beetle makes its way out of this cavity by pushing out the plug 
at the end of the twig, and never, according to our numerous in- 
sectary observations, by cutting through the wall of its cell. 
As an example of the observations from which these biological 
data are derived, the following abstract from the insectary notes of 
one of the 1905 experiments may be given. They were written 
alternately by R. M. Webster and J. J. Davis, entomological stu- 
dents in the University of Illinois, serving as insectary assistants at 
the time. 
On the 22d of July twigs of the elm containing Obcrca larvse, 
sent by Mr. Taylor from Decatur, were transferred to living elms 
at the insectary, either by carefully grafting the infested twigs into 
those of a growing tree or by hollowing out in the living twigs 
artificial cavities in which Obcrca larvae were separately placed. By 
the 25th of July evidence of the activity of these transferred larvae 
was seen in the wood dust on the infested twigs; and by the ist of 
August one of the larvae had passed the graft from its original twig 
into the living stub on the tree, and had made a hole for the wood 
dust an inch beyond this point. 
