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1915-16.] Structure and Life-History of Bracon sp. 
Life-History of Bracon sp. 
Living a large part of its life in the tunnels of the Hylobius grub as 
it does, this Bracon is not easily studied in the field. In order to find 
it the bark must be removed from the stumps, and the larvae or cocoons 
exposed, and there is an end to field observations on that particular brood. 
The life-history of the individual cannot well be studied in the field, and 
accordingly it was worked out in the laboratory. 
The best means of obtaining the Bracon is to collect its cocoons just 
before spring sets in, during March and April. As the adults emerge 
from their cocoons, they are paired off and provided with pieces of bark 
containing the grubs of Hylobius. My method was as follows : — Hylobius 
grubs still feeding in the bark were brought in from the field. A large 
piece of thick bark was cut into small pieces. In each piece a hole 
the size of the larval tunnel was bored, and into each hole a healthy 
uninfected grub was placed. The grubs continued boring in the bark so 
provided, and the method proved quite successful. Each pair of Bracons 
was provided with one or more grubs in this way. 
The following account of the life-history is based on observations in 
the laboratory : — 
Pairing. 
Both sexes are sexually mature on emergence, and pairing takes place 
almost immediately. The act is of short duration, and, so far as has been 
observed, is not repeated on the part of the females. 
Oviposition. 
Egg-laying may take place within a few hours of pairing, or it may 
be delayed for several days. 
While my knowledge of Bracon was restricted to field observations the 
problem of oviposition was for long a puzzle to me. On the 3rd of June 
1914 I had an opportunity for observing a Bracon in the act of egg-laying. 
The female in question had paired on 1st June. On the morning of the 
3rd she appeared very restless, and towards mid-day she was busily 
engaged digging away the frass from the entrance of a weevil grub’s 
tunnel in the bark supplied her. She stood firmly on her middle and 
hind legs, and, working excitedly with her fore legs, raked back the debris 
in front of her. Meanwhile her antennae, continually vibrating and moving 
to and fro, seemed to direct her towards her prey. After some minutes’ 
work she reached the chamber in which the grub was lying, and inserted 
first one antenna and then the other. Apparently satisfied, she retired a 
little, and then, turning round slowly, she backed towards the entrance she 
