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Life-history of Melittobia acasta 
course of time the eyes of the female pupa become red and shortly before the 
emergence of the imago, the whole pupa becomes black while that of the male 
becomes reddish brown. The duration of the pupal period under the most 
advantageous conditions is about seven days. 
But both larval and pupal periods vary very considerably in their duration 
under different conditions. So far as I know, the species normally hibernates 
in the larval stage and such larvae, as I have already mentioned, may not 
pupate until the following July, so that we have the shortest larval period 
as eight days and the longest as about eleven months. The pupal period also 
varies between about seven days and perhaps ten months. 
V. The Habits of the Female. 
(i a ) Food and method of feeding. 
The female feeds upon the blood of her host which she obtains by 
puncturing with her ovipositor. A hungry female walks about upon the host, 
be it egg, larva or pupa, tapping it with the apices of her antennae until she 
selects a suitable spot. She then bends the apex of her abdomen downwards 
and thus brings the point of her ovipositor into contact with the surface of 
the host (Plate XXVI, fig. 8 a). The ovipositor is then released from its sheath 
by the abdomen straightening again and the insect by a steady or, may be, 
a slightly jerky pressure of the body forces the apex of the ovipositor through 
the “skin” of the host (Plate XXVI, fig. 8 h). The stylet may be driven in 
deeply, even to its base, or it may merely penetrate but, after a short interval, 
it is withdrawn and the insect rapidly moves backwards, feeling about with 
her antennae until the puncture is discovered, when the mouth is at once 
applied to it (Plate XXYI, fig. 8 c). After sucking for a short time, the insect 
moves away and may at once repeat the process at some other spot. 
One would scarcely expect that the egg or young larva of a bee or a wasp 
could suffer this treatment and survive and yet I have had many examples 
of eggs punctured, even so that a globular effusion of “blood" appeared upon 
the surface, without the vitality being, to all appearance, affected. I have 
placed as many as 15 Melittobia females in a cell with a newly hatched larva 
of Osmia and have allowed them to feed freely upon the host for a fortnight, and 
yet ultimately these heavily taxed hosts have pupated and emerged as adults. 
In the same way Melittobia females placed in cells with older host larvae 
produced no ill-effects so long as they were only feeding and I am therefore 
cpiite satisfied that the feeding habits of this parasite are not necessarily 
injurious to the host. 
(b) Preparation of food for the larvae. 
On the other hand, once a Melittobia female lays an egg upon its host, 
whether the latter is in the egg, larva or pupa stage, the host is apparently 
doomed. This seemed at first a most extraordinary thing. It was difficult to 
