26 
Journal of Agricultural Research 
Vol. II, No. x 
braconids and 15 chalcidoids. Nine of these chalcidoids are known to 
be new species, and they have recently been described by Mr. J. C. 
Crawford, Associate Curator of the Division of Insects, United States 
National Museum. Three others are probably new, but as there is only 
a limited amount of material they can not be recorded as new with 
certainty. Two of the braconids are new also. 
With this army of parasites in the field it will be readily seen that the 
chances that the miner will do serious mischief are reduced to a mini¬ 
mum. Only under exceptional circumstances would Agromyza parvi- 
cornis be able to elude this array of enemies. This is a very good 
illustration of the holding in check by its natural enemies of what would 
otherwise in all probability be a pernicious insect, thus showing that it 
is entirely possible for a group of parasites under favorable conditions 
to control their host insect. 
The life history of none of these parasites has been worked out com¬ 
pletely. 
Of these parasites Derostenus diastaiae is by far the most abundant 
and probably the most important. Diaulinus websieri and D. begini 
have also been reared quite plentifully and are probably next in im¬ 
portance. An effort is here made to discuss these parasites in the order 
of their importance without regard to their systematic relationship. 
Derostenus diastatae How.—This chalcidoid very closely resembles ZL 
punctiventris (PI. V, fig. 1). It is an internal parasite and was first 
reared in 1879 from a corn-leaf miner which was called at the time 
Diastata , n. sp., but which has since been determined as Agromyza parvi- 
cornis . The parasite was described by Dr. L. 0 . Howard as Entedon 
diastatae. It appears to have been very abundant at that time. Prof. 
Comstock (1881) writes: 
During the season of 1880 these leaf-miners were extremely difficult to find, which 
was doubdess owing to the very extensive parasitization of the 1879 individuals. 
Out of thirty or forty specimens examined but one contained a sound larva, which 
was reared to maturity. All the rest contained several minute parasitic larvae. 
Prof. F. M. Webster reared this parasite in 1886 at La Fayette, Ind., 
from what was probably this miner. He reared large numbers of the 
same species at Urbana, Ill., in 1902, from a miner in grass. It was 
reared by Mr. C. N. Ainslie at Washington, D. C., in 1907, and by Dr. H. 
Kraemer, of Philadelphia, in 1905. In these two last instances it was 
parasitic upon a miner in grass leaves. Mr. G. G. Ainslie reared what is 
doubtfully the same species at Clemson College, S. C., in 1908. The 
host in this instance was probably Agromyza parvicornis , as it was a 
blotch miner in corn. He also reared it in abundance in 1911 and 1912 
from a miner in corn leaves at Hurricane Mills, Tenn. Mr. T. H. Parks 
reared numbers of this parasite from a blotch miner in com leaves at 
Wellington, Kans., in 1909. The same parasite was reared in abundance 
by the author from A. parvicornis at Richmond, Ind., in 1911, and at 
