THE CAMBIUM MINER IN RIVER BIRCH 
By Charles T. Greene, 
Entomological Assistant, Forest-Insect Investigations, 
Bureau of Entomology 
The species of the family Agromyzidae generally mine in the leaves and 
stems of various plants, while some mine in their roots. The species pre¬ 
sented in this paper, Agromyza pruinosa Coq., 1 is quite out of the ordinary 
in that it mines in the cambium of the living tree, the mine leaving a scar 
known as a “ pith-ray fleck.” 2 These flecks in the various kinds of wood 
have been known for many years to be the result of the work of insects, 
and extensive investigations have been carried on in Europe as well as in 
this country in order to determine the species causing the damage. In¬ 
vestigations in Europe have proved that at least the pith-ray fleck in 
birch may be accredited to Agromyza carbonaria , 3 which is closely related 
to the American species. The pith-ray flecks in birch in America have 
been studied carefully, and it has been decided that Agromyza pruinosa is 
at least one of the insects that produce flecks and is possibly the only one. 
A gromyza pruinosa taken from river birch has just been reared to maturity. 
This is the first record in America of the production of flecks in birch by a 
definitely known species. (PI. LX, fig. 2.) 
SEASONAL HISTORY 
During July and the early part of August, 1912, the work of this 
dipterous larva was very common in river birch at the Chain Bridge, in 
the District of Columbia, every tree that was examined containing new 
work; but in 1913, in the same locality, only a few trees disclosed new 
work. A dipterous larva and similar work were found frequently in 
red maple (Acer rubrum ), but not so commonly as in birch. In 1913 
Mr. T. E. Snyder found in wild cherry (Prunus sp.) on the Virginia shore 
of the Potomac River at the Chain Bridge two larvae which are identical 
with the larvae of Agromyza pruinosa in the birch, except that they are 
only two-thirds as long, although to all appearances full grown. The 
work of this species in wild cherry is identical with that in red maple 
and black birch, but the mines are correspondingly smaller. 
1 Thanks are due to Mr. J. R. Malloch for assistance in determining the species. 
* Brown, H. P. Pith-ray flecks in wood. U. S. Dept. Agr., Forest Serv., Circ. 215, 15 p., 6 pi. May 7, 
1913. 
3 Nielsen, J. C. Zoologische Studien iiber die Markflecke. Zool. Jahrb., Abt. System., Geogr. u. Biol. 
Tiere, Bd. 23, Heft 6, p. 725-738, pi. 30. 1906. 
(471) 
Journal of Agricultural Research, 
Dept, of Agriculture, Washington, D. C. 
Vol. I, No. 6 
Mar. 25, 1914 
K-s 
