323 
1915-16.] Structure and Life-History of Bracon sp. 
areas in the surrounding district were now examined, on the supposition 
that the liberated Bracon had gone beyond the area of liberation. All of 
them, three in number, proved of recent date, and contained no Hylobins. 
Conclusion and Summary of Field Experiment. 
The field experiment had a double purpose: (1) to try the effect of 
liberating large numbers of Bracon ; (2) if this had been successful, to 
obtain a mass of material for an experiment on a much larger scale. 
The non-success of the field trial at Drumshoreland, as contrasted with 
the success of the laboratory experiments, can be explained partly by the 
unfavourable nature of the weather during the period of liberation of the 
Braconid parasites, and partly by the fact that the area for experiment 
was too circumscribed, so that the liberated Bracons wandered. 
Laboratory Experiments. 
The material used in the laboratory was collected during October 1914 
and May 1915 in Aberdeenshire. As the adults emerged from the cocoons 
males and females were taken and placed in breeding-cages. These con- 
sisted either of a wooden cage with a glass front and fine-mesh gauze sides, 
or simply of a glass jar with a double fold of fine muslin over the opening. 
The bottom of each of these cages was covered with a layer of moss, which 
was kept constantly moist. Hylobius grubs were supplied in small pieces 
of Scots Pine bark in which they had begun to tunnel. This method 
proved quite satisfactory, and approached natural conditions fairly closely. 
It ensured that no grubs which were already parasites were introduced, 
and that the grubs were healthy and active. They were also easily 
examined. 
Series 1. 
My first experiments were carried out with cocoons collected in October 
1914 and kept in the laboratory through the winter. The following are 
the records of them : — 
Hxpt. No. 1. 
1915. 
March 1. Newly emerged male and female placed in cage with bark con- 
taining a Hylobius grub. 
„ 17. 2 Braconid larvae hatched ; they measured 2 mm. in length, and 
were feeding on this grub, which was soft and flabby. 
„ 20. Hylobius grubs putrefied. Braconid larvae dead. 
