A CHALOID PARASITE OF DIPTERA. 
A Chalcid Parasite of Diptera. 
By H. M. NICHOLLS, Government Microbiologist, Tasmania. 
Last summer, the writer collected several specimens of a very 
curious parasite of March flies and other dipterous insects. He first 
found it about fifteen years ago on March flies, blowflies, and a large 
fly belonging to the Dexiidw, in the Huon district, but never saw it 
again until quite recently. It is so minute that it is barely visible to 
the unaided eye, and is ovate in shape and of a dark-brown colour. The 
body is composed of thirteen strongly chitinised segments, and the head 
is provided with a pair of very strong hooked jaws, with which the 
parasite attaches itself to the pseudo-tracheal tubes of its host. When 
removed from the host it can crawl about quite actively with a ecater- 
pillar-like motion, and seems at home when placed in water. 
Its nature remained a mystery for many years, as the writer had 
no opportunities of breeding it to ascertain its life-history, until light 
was thrown on its affinities by the publication of an account of the 
discovery of a somewhat similar creature in America, which was found 
as a hyper-parasite of the larve of Limnerium validum in the cater- 
pillars of ‘the fall web-worm, Hyphantria textor. ‘The American specl-. 
men was found to be a stage in the development of a chalcid belonging 
to the genus Perilampus. Dr. W. M. Wheeler, it appears, had pre- 
viously discovered a somewhat similar stage in the life-history of 
another chalcid, Orasema viridis, and had proposed the * name 
“planidium” for it, to indicate the motile and wandering habits that 
at this stage it possesses. 
The specimens found in Tasmania. differ somewhat in anatomical 
details from the descriptions of the American varieties, but the general 
plan of construction is exactly the same, and there is no doubt that this 
very curious litile creature is the planidium stage of one of our native 
chaleids. In its habits it differs from its American congeners, as it 
appears to be entirely an ecto-parasite, spending the whole of its larval 
existence attached to the proboscis of its host. Specimens are oceca- 
sionally found which have fed until they have swelled up to an extent 
which separates the chitinous plates of the body and causes the parasite 
to assume the appearance of a small globe of a whitish colour, and .a 
somewhat similar appearance is shown in the drawings of the planidinm 
stage of Perilampus. oe 
This parasite is sometimes found in great. numbers, especially on 
species of Tabanus, One Tabanus proboscis in the possession of the 
writer has no less than 74 adhering to it. When attacked to this extent 
the flies seem to be rendered ineapable of feeding properly, and become 
weak and sluggish. It may be mentioned that these little creatures hold 
on like bull-dogs, and it is generally impossible to remove them with- 
out tearing away some portion of the proboscis with them. Some of 
the mounted specimens in the writer’s collection still have a mouthful 
of pseudo-tracheal tubes in their jaws. It is probable that this parasite 
is really very common, but it is so minute, and spends its larval exist- 
ence in such an unusual situation, that it is not likely to ever come 
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