F. B. Browne 
357 
believe that the mere fact of the parasite egg being in contact with the body 
of the host could cause the destruction of the latter and the experiment of 
removing eggs from one host and placing them upon another with which no 
Melittobia female had come into contact proved that the parasite egg itself 
in no way affected the host. 
This point puzzled me for some time as it seemed that the only explanation 
was that the Melittobia possessed some subtle instinct by which it knew when 
a host was moribund and that, in such a case, the parasite oviposited on what 
was really an unsuitable host. What seems to be the real explanation came 
to me accidentally. With a high power binocular microscope, I was watching 
a Melittobia female puncturing a mature Odynerus larva and I happened to 
notice a fluid oscillating in the semi-transparent ovipositor. Gradually the 
ovipositor was buried to its base in the host and after an interval of about 
two minutes it was withdrawn and I was surprised to see the insect move 
away without making any attempt to find or to suck the puncture. This, 
then, appeared to be a different process from the feeding one and I made a 
number of experiments with ripe female Melittobias, i.e. females which had 
already begun to oviposit, isolating individuals in glass cells each with a host 
suitable for oviposition, the host in every case being a resting larva of either 
an Osmia, an Odynerus or a Chrysis. 
By watching these females it was easy to establish the fact that they 
frequently made punctures without afterwards sucking them and occasionally 
it was possible to imagine a fluid passing down the ovipositor into the 
wound 1 . 
As soon as I saw a host larva punctured in such a manner, I transferred 
it to a separate cell and left it, with the object of seeing whether it would 
ultimately become a pupa and emerge in the normal manner. In some cases 
these larvae may have been thus punctured only once and in other cases they 
may have been punctured a number of times but they were always removed 
from the parasite before the latter laid any eggs upon them. All but one of 
these larvae, numbering thirty-eight, failed to develop. 
In another set of experiments, involving twenty Odynerus larvae in the 
resting stage, I allowed Melittobias to lay a few eggs upon them, always 
removing the eggs before they hatched and removing the females after a few 
days and in all these cases again the Odynerus larvae failed to pupate. 
It seems therefore that the Melittobia female punctures her host for two 
different purposes, one in order that she may feed upon its ‘"blood” and the 
other in order that she may inject something so as to stop the development 
of the host for the benefit of her offspring. 
1 1 have used the word “imagine 5 ' here because it is extremely difficult to make the observation, 
it being necessary to get the parasite in a particular position with regard to the light and, of course, 
to see the ovipositor before it is driven in to its base. The only case of which 1 am absolutely 
certain that I saw a movement of fluid in the ovipositor from parasite to host was one in which 
a female was puncturing a fly puparium but, as in the case of fly puparia the parasite lays its 
e gg on the fly pupa contained within the puparium, I may have been watching the passage of eggs. 
