'^16 DISEASES OF INSECTS. 
of the same description ; and I even saw one upon its 
wing. Upon a former occasion I mentioned a parallel 
circumstance with respect to a species of Xylocopa a . 
ii. The animal parasites that infest insects are cither 
themselves insects ; or worms. 
1 . Their insect infesters, as far as we know at present, 
are confined to the Orders Strepsiptera, Hymenoptera, 
Diptera, and Apt era : they attack them sometimes in their 
egg state, most frequently when they are larvae, occasion- 
ally when pupa?, and very rarely in their perfect state. 
Upon many of these I have formerly enlarged b , and 
I shall now add such further circumstances as I then 
omitted. The Strepsiptera Order, as at present known, 
consists only of two genera, Stylops and Xeiios ; the first 
being appropriated to the imago of Andrena, a kind of 
bee, and the latter to that of the 'wasps. Their eggs ap- 
pear to be deposited in the abdomen of these insects in 
which they feed, till having attained their full growth 
they perforate the membrane that connects its segments ; 
andat the proper time their pupa-case bursts, they emerge, 
and take their flight. Sometimes four or five infest a 
single bee. Whether the latter dies upon their quitting 
it I have not been able to ascertain, but from their fly- 
ing, when the little parasite is very near leaving them, 
with their usual activity, it should seem that this disease 
is not mortal ; but it probably prevents their breeding : 
I do not recollect observing the exuviae of one in a male 
bee c . 
The great body of insect parasites, however, belong 
to the Hymenoptera Order, and chiefly to the Linnean 
genus Ichneumon. The insects of this order have been 
* Vol. III. p. 335—. " Vol. I. p. 267—. 
A}>. Angl. ii. 111. Linn. Trans, xi. 90—. 
