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their own order), but the Diptera are exempt, at least it is safe to say 
comparatively so, from true parasitic attack. The second and final sig- 
nificant fact is that the Diptera are the only order of insects which has 
become truly parasitic (endoparasitic) on mammals, including man 
himself. This fact of the dipterous parasitism on Mammalia seems the 
most remarkable and striking of all. 
Of these three parasitic orders, our subject deals with the last named, 
the Diptera, and more particularly with the parasitic members of the 
order in their economic relations. It has been noted that the Diptera 
afford the most generally distributed amount of parasitism, covering the 
entire field of orders subject to parasitic attack. Let us separately con- 
sider the families of Diptera which contain parasitic members. 
(1) Cecidomyiidce. — A number of cecidomyians are known to be par- 
asitic on Coccidae and Aphides. Prof. J. H. Oomstock found a Diplosis 
in California parasitic on Coccids. Mr. T. D. A. Cockerell has found 
a similar parasitic species in Jamaica. A number of other cases had 
been previously recorded, and they apparently all belong to the genus 
Diplosis, though one is referred to Cecidomyia. The parasitism in this 
family, comprising as it does the only cases in the Nemocerous Diptera, 
is extremely interesting, since the Nemocera are the most ancient living 
forms of Diptera. It should be noted also that the parasitism here is 
confined to a few members of a single genus. About eight North Amer- 
ican genera are known, some being very numerous in species. 
(2) Nemestrinidce. — Two North American genera are known. The 
genus Hirmoneura is recorded as parasitic on wood-boring coleopterous 
larvae. A European species is said to deposit its eggs in the burrows 
of a buprestid, to which the larvae attach themselves by means of hooks 
on the segments, but later lose the hooks and become parasitic on a 
secondary host, a beetle of the genus Ehizotrogus. 
(3) Bombyliidce. — In this family over thirty North American genera 
occur. These flies are all, so far as known, parasitic on insects of the 
orders Lepidoptera and Hymenoptera. There is only the exception 
that the larvae of Aphcebantus and Systcechus have been found to feed 
on the eggs of locusts. It is the peculiar habit of this family to attack 
insects which live underground, such as certain bees and wasps, and 
cutworms. 
(4) Acroceridce.— About eight North American genera are known, 
The larvae are, so far as known, parasitic on spiders and their egg- 
masses. It is worthy of note that this is the only dipterous family 
parasitic on spiders. 
(5) Conojpidce. — This is another family which contains purely para- 
sitic species. Seven North American genera occur. All are parasitic, 
without known exception, upon Hymenoptera and Orthoptera, princi- 
pally upon bees and wasps, whose appearance they have acquired. 
(6) Pipuncalidce. — The larvae of some species of the single genus 
Pipunculus are known to be parasitic on homopterous insects of the 
family Jassidae. 
