NATURAL ENEMIES: PAKASITIC INSECTS. 33 
The related species, especially bullatus Say, uliginosus Say, and 
borealis Dall, which are equally common over most of the country, 
certainly must contribute largely toward the reduction of the leaf- 
hopper pest. 
PARASITIC INSECTS. 
We have, in the parasitic insects affecting the members of this 
group, another most constant means of control, and one which is 
perhaps far more important than we readily appreciate. Among 
these forms are numbers of Hymenoptera, Diptera, and Strepsiptera. 
Of the Hymenoptera the most abundant parasites are included in 
the families Proctotrypidse and Dryinidas in the genera Gonatopus 
and Dryinus. These parasites affect the larvse more particularly, but 
are often found upon the adults and are conspicuous, inasmuch as for 
many of the species the parasitism takes the form of an external 
sack-like structure in which the larva develops on material sucked 
from the body of the host. In some of our native species these 
parasites have been found present in something like 20 per cent 
of the individuals, so that it is evident that they must constitute a 
quite distinct check upon the leaf hoppers. An extensive series of 
records showing the parasitism of these forms is found in the reports 
of the Hawaiian entomologist and in the papers of Perkins and others 
in connection with investigation of leafhoppers affecting sugar cane. 
Many species were collected and reared from leafhoppers occurring in 
the United States for the purpose of introducing them into the 
Hawaiian Islands in hopes that they might prove of service in control 
of the sugar-cane leaf hopper (PerJcinsiella saccharicida Kirkaldy). 
A detailed account of these species would hardly be in place here, 
but the importance of tins source of control is sufficient to make 
it worthy of further investigation. 
Among the Diptera a genus, Pipunculus, is recorded as parasitic 
upon leafhoppers, and Giard is authority for the opinion that these 
are in general parasites, especially of the family Jassidas. These have 
not been recognized to any great extent in this country, and we are 
unable to say to what extent they may have a service here. 
The order Strepsiptera, or the twisted- winged insects, includes 
some very peculiar and remarkable parasites, numbers of which have 
been recognized as occurring on leafhoppers. These parasites are 
so minute and inconspicuous that they are very seldom observed, 
and we have no very positive data as to the numbers in which they 
may occur, so while they may be a very constant factor in control, 
it is doubtful if they can be credited with very much influence in 
reducing the numbers. The group is one of special interest on 
account of the peculiarity of structure and habit, and is one which 
may well be given much more extended study than it has yet received. 
