368 
Life-history of Melittobia acasta 
a larva or pupa to change of temperature is slight but that of the imago is 
more marked, since once the imago appeared she behaved exactly like a 
summer individual and passed on her activity to her eggs, larvae and pupae. 
The apparent irregularity of the action of increased temperature on different 
individuals in the same batch (e.g. 21 to more than 67 days in Batch 1) is 
perhaps to be accounted for on the assumption that the individuals in a batch 
differ considerably in age. 
XIII. Means of Dispersal of Melittobia. 
In the course of the season there may be two to five and even more genera¬ 
tions of Melittobia so that, but for the cannibalism amongst the larvae and 
the poor means of distribution available for the species, this parasite would 
be a very serious menace to a very large number of species of bees and wasps. 
Yet, as a matter of fact, in the Cambridge district I have only succeeded 
in finding one old clay wall of a few square yards in extent from which I have 
been able to get my supplies of material and even from this wall, after three 
or four years, there are still Odynerus spinipes emerging, although what used 
to be a very large and flourishing colony is now reduced to very small numbers. 
Now the females can apparently only fly an inch or two at a time and, 
for the most part, they do not use their wings. I have never lost a specimen 
by letting her run about upon the laboratory table when I have wished to 
clean out her glass cell. 
These females run about fairly rapidly and are active and it is quite easy 
to see how they might quickly overwhelm a colony of a host species once they 
reached it but it is the passage from one colony to another that is difficult 
to understand. 
Walker mentions that the species occurs “on windows" and although I 
have not so far found it in such situations, this suggests to me a possible 
means of dispersal. I cannot imagine Melittobia deliberately walking into a 
house and then becoming positively heliotropic, but, when wandering about the 
haunts of solitary wasps and bees it may occasionally mount upon these, and 
thus be transported to other haunts whereby it would occasionally be bumped 
off against the window-pane. 
XIV. Summary. 
Melittobia is a chalcid, ectoparasitic upon a number of species of Hymeno- 
ptera and upon the pupae of certain flies. The insect was bred in the laboratory 
and the life-history is described in detail. 
A number of experiments were made with regard to possible hosts and as 
to feeding and reproduction and certain points are of some interest. 
For instance, the male apparently does not feed but the female uses her 
ovipositor with which she punctures the eggs, larvae or pupae of various 
insects, afterwards sucking the blood which oozes from the puncture. Such 
eggs, larvae or pupae, in spite of repeated punctures, may continue to develop. 
