350 Life-history of Melittobia acasta 
The insect first came under my notice in 1918 when I was watching the 
habits of and making experiments with certain solitary bees and wasps in my 
garden in Cambridge. I had started there a small colony of Odynerus spinijpes 
by bringing home pieces of an old mud wall containing larvae from a ruined 
cottage at Histon and I had attracted various other wasps and bees by 
providing glass and elder tubes arranged on shelves attached to my garden fence. 
On the 30th May of that year I noticed that a minute Chalcid was swarming 
over one of the pieces of the mud wall and later freely entering tubes which 
were being occupied by bees and wasps and, in the case of glass tubes so 
occupied, I noticed that numbers of this minute insect became sealed up in 
the cells constructed by the bees or wasps. 
At first I thought that these imprisoned individuals had been caught 
accidentally in the cells and that they would quickly perish but, on watching 
them, I noticed certain acts which caused me to form a different opinion. 
I therefore began to investigate the life-history and by the autumn of that 
year I had worked it out and it was not until I was describing some of the 
curious habits of this little parasite to my friend Dr Keilin that he referred 
me to Malyshev’s paper which he very kindly translated for me. I then found 
that, although in the main my observations agreed with those of the Russian 
author there were various points upon which I differed from him and I there¬ 
fore decided to work out the life-history again and to make some further 
experiments. 
It was not until January 1921 that I was again able to obtain the necessary 
material as I had allowed all my stock to die out after completing my observa¬ 
tions in 1918. 
(b) Technique. 
In order to watch the life-history of and to experiment with this minute 
insect I made a number of cells by cutting pieces of glass tube of about 
8 mm. diameter gauge into 3 inch lengths and fixing these horizontally to 
small pieces of cardboard by means of thin wires (PI. XXVI, fig. 9). Into the 
middle of such a piece of tube a wad of cotton wool was pushed and rammed 
tight, the wad being about half an inch long. Each end of the tube plugged 
with a similar wad gave me two cells to each tube. I found that these cotton¬ 
wool plugs were sufficient to prevent the escape of the insects under ordinary 
circumstances since, if the female is placed under conditions which give her 
suitable food and suitable material for the reception of her eggs, she makes 
no effort to escape. If however females were retained in such a cell without 
food they frequently attacked the plugs and when they were numerous—as 
when a whole brood hatched out and was left in a cell, they frequently bit 
their way out. It is curious to notice that under these circumstances, the 
central plug was seldom, if ever, attacked and presumably the insects were 
guided to the end plug by air currents through the wool. The cardboard to 
which the tubes were attached made them stable and upon it numbers and 
dates referring to the imprisoned insects were written. 
