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Psyche 4:195-199, 1883.

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NOTES ON THE RELATIONS OF TWO CECIDOMYIANS TO FUNGI.
BY WILLIAM TRELEASE. MADISON, WISC.
For some years, while collecting the
commoner uredineae or rust fungi, my
attention has been attracted by certain
small orange-red insects, that are very
frequent in and about some of the sori.
They ale most often noticed in the aeci- dia or cluster-cups and in those sori
which contain ut-edo-spores. At times
they are so abundant that it is almost
impossible to collect a specimen of the
commoner uredo or aecidial forms with-
out finding numbers of them in nearly
every sorus.
A first glance at them suggests that
the insects may he some species of
Thyits, but the resemblance vanishes
on closer ex~imination. Their motions,
as a general thing, are less rapid than
those of Tht-i's. and a hand-lens at
once shows them to be some sort of
dipterous larvae. "With a higher power
the breast-bone. characteristic of ceci- domyid larvae. is distinctly seen. Vari- ous attempts have been made to bring
them to maturity, but so far without
success, so that it is as yet impossible to say :in-\ thing definite about the spe- cies to which they belong.
The constant presence of these insects
on the fruit of the fungi led me to watch their movements from time to time, and
the reason for their presence was soon
seen in the altered appearance of the
sori where they were most numerous.
Their relish for the spores is entirely
disproportionate to the size of their mi- nute bodies. The fact that they feed
on the spores affords a simple explana-
tion of their presence on the aecidial
and uredu fluits, rather than in the te- le~itosporic sori of the rusts, since the spores of the latter are more frequently thick-walled and hard.
The fungi on which I have most often
observed the larvae in qiiestion are Aeci- dium calaw the cluster cup of Ari-
saema and other aroicls. Coleosj4oriuiw
sowchi-arvemis, the common rust of As-
ter and Solidago. and Caeoma nite9z.s.
the destructive red-mst everywhere
abundant in spring on leaves of the
blackberry and raspberry (Rubus).
Mr. C. V. Riley informs me that he
has also found the same larvae on a fun- gus (Exohasidium vaccinii?) growing'
on Azalea, and that the! have been




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seen absolutely swarming on some flesh-
colored fungus coverings squash, C-itcw- bita. The same, or very similar insects
occur also in Europe, for M. Patouil-
lard, speaking of Caeoma e?~onymi and
Aecidium convallariae in the vicinity
of Paris, says that their spores are fre- qucntly devoured by a small larva of an
orange co1or.l
These larvae differ in their fungivo-
roiis habits from the greater number of
ceciclon~~ ians, which feed on the juices of phaenogams, causing atrophy, as in
the case of wheat attticlid by Cecidomyia destructor, the hessian fly, or the de-
velopinent of galls such as most of the
cecidomyidae produce. Some species,
notably Cecidomyia tritici. the wheat
fly, feed upon pollen, at least in the
early part of their lives, in this respect approaching' the species which eat
spores. Aside from these, there are
a few anomalous feeders in the genus.
Westwood2 states, on the authority of
Vallot, whose work I have been unable
to consult, that the larvae of one species are found on the under side of leaves of CJieZidonium, sucking the acari found
there ; and Cecidoniyia bicolor Meig.
is said by Macquai-t to frequent the
iinclersicle of the leaves of Leonnr-ns. possibly for a similar purpose.
While the fnngus-eating species are
not sufficiently restricted in their choice of food to be classed as entirely injuri- ous or entirely beneficial, they would
1 Bull. soc. hot. France, 28 May 1880, v. 27, p. 162. Introcl. to mod. class, insects, v. 2, p. 519. naturally fall among the useful species. Even the golden-rods and asters are of
some importance to bee-keepers, and
the onslaughts of the insects on the
spores of the raspberry rust and other
parasites of cultivated plants must tend to check the spread of these fungi, so
that in a measure they protect the flow- ering plants on which they live, as does the species referred to by Vallot.
.E~~tomologists are familiar with cer-
tain black spots, several millirnetres in diameter, in the leaves of golden rods
and asters. ,Ydidago Zanceol~ta and
5'. temiifuZia are more frequently
marked in this manner than other spe-
cies. These objects are found in the
cabinets of economic entomologists as
the galls of a gnat, Cecidomyia carbon-
ifera 0. S. They also occur in the
herbaria of mycologists as fiingi, under the names Rhytisma soZz'daginis. and
R. asteris given them a half century
ago by Schweinitz,
On narrow-leaved species of Solidago,
e.g., S. lanceolata, the spots, visible
on both surfaces of the leaf, are some-
times almost circular, varying in cliarn- eter from I to 4 mm. ; but more corn-
monly they are elongated parallel to
.
the axis of the leaf, so as to be ellipti- cal or oblong-. They are usually sym-
metrical. unless the centre is situated
at one side of the midrib of the narrow
leaf, in which case the corresponding
side is necessarily truncated on reaching the margin. The leaf is always slight-
ly swollen in the discolored spot, but




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198 PSYCHE. [ August-September 1884.
cente. Dehiscens non rnihi obvium. In planta uhi occurrit plerurnque frequenter infestat folia. - Srhivefn- itz, Syn. fung. Arner. bor. (op. cit., p. 241.) It has been seen that the single or
double convexity of these galls is not
available as a distinctive character, al- thong11 Schweinitz makes use of it.
One of the most obvious superficial
characters is the presence or absence of a white, gray or yellow membrane over
the carbonized portion of the leaf.
This, the velum of Schweinitz, is how-
ever by no means constantly absent 01-
present in the same species, if we ex-
cept that on So/idago ZanceoZata, where
I have never seen it. On the same
plant of S. ulmifoZia some spots are
black, while others are invested on both surfaces by the yellowish-white incl~isi- nin ; and one of the Osten Sacken types
of the gall of Cecidomyz'a carbo+fera,
on a broad leaved Solidago, for an ex-
amination of which I am indebted to
the courtesy of Dr. H. A. Hagen, is
black above, with a narrow white bor-
der, while below it is completely cov-
ered by a white indusium, broken here
and there as if by accident. With age
this membrane frequently breaks away,
but in the specimens to which the pre-
ceding statements refer the leaves were
intact, and its absence was clearly not
due to removal.
In their microscopic characters, all of
these forms show a general agreement.
The parenchyma of the leaf is invaded
by a colorless mycelium of thick-walled
hyphae, which lives between the cells
and to a certain extent deforms them.
It excites little if any hypertrophy, but by crowding the cells apart in its own
growth causes the slight convexity of the part of the leaf in which it occurs.
Near the surface the rnycelial threads
become brown, apparently as the result
of some chemical action due to the fun-
gus, which also aflects the surrounding
cells of the leaf, some of which are so
completely carbonized that their walls
are coal-black. In R. soZidaginis and
the other exindusiate forms, the epider- mis is especially influenced by this
change, which, however sometimes does
not extend so far laterally as in the un- derlying tissue, - a fact which at once
explains the pale border sometimes no-
ticed ; the dead but colorless epidermal cells at the margin of the spot. filled
with air. appearing white, and contrast- ing strongly with the carbonized cells
on the one hand and with the living ones on the other. The indusium of the other
forms is of a similar nature to this border. consisting merely of the dead epidermis, filled with air ; but why the epidermis
should be blackened in some cases and
remain colorless in others it is hard to say.
From what precedes it will be seen
that only two of the three so-called spe- cies of Rhytisnza are certainly (listin- g~iishable in the specimens that I have
extiinined, \ iz : 22. solidaginis, on So- lidago Zanceolata and S. tenuz~olia,
and R. asteris (including R. bifrons)
on Aster and the broader leaved spe-
cies of Solidago.^ Curtis, whose her-
barium, containing many Schweinitzian
specimens, I have examined, through
.
3 The latter are referred by Berkeley to R. solidayinis (Grevillea, v. 4, p. 8).




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the kindness of Professor W. G. Farlow.
was evidently of the same opinion, for
his specimens bear only these two names, though some of the last named species
occur on Solidago, and one, on Aster
gracilis, agrees very well with the de-
scription of JR. bzfrons. Schweinitz,
also, says of the three so-called species " Tres species antecedentes memorabiles
inter se affines sunt."* The fruit of
all is unknown. Like that of other species of Rhytisma, it does not develop on the
living leaf. and I have been unable to
look for it on the fallen leaves late in autumn or on the approach of the fol-
lowing spring. Possibly, when found,
it may ofter a means of distinguishing
the so-called species more satisfactorily than can be done at present. Both spe-
cies ak widely distributed over the east- ern third of the continent, from the Gulf states to New Brunswick.
The discussion of these objects from a
botanical standpoint may appear to
some readers unnecessary in an entomo-
logical journal, but no account of them
would be complete without it. Turn-
ing. now, to the entomological side of
their history, it remains to be said that several entomologists have bred from
them one of the gall gnats - Cecidomyia
cado+fera Osten Sacken. I, myself.
have obtained the adult insects from
what I have called JR. asteris, and they are to be seen in some of the specimens
in the Curtis herbarium, which have
been broken. The Osten Sacken types.
in the Museum of comparative zool-
ogy, would also undoubtedly be referred
4 Syn. fun& Am. hor., l. r., p. 241,
to this species by a mycologist.
With
the form on Solidiigo lanceolata I have
been less successful, having never ob-
tained the imago from it ; but in the
summer of 1881, while at Woods Holl,
Mass., where this form was exceedingly
common, I examined several hundred
specimens on this plant, by breaking
.
them open, and in every instance a liv-
ing larva, evidently a cecidomyid, and
apparently Cecidomyia carbonifera.
was found in the substance of the gall,
where it lay in a minute cavity.
So far
as I know, therefore, both insect and
fungus are always present in these galls, to whichever species they are referred.
While the slight convexity of the young
gall is explained by the growth of the
fungus, the hemispl~erical enlargement
in many cases, especially on asters, seems to be caused by the insect, and these very thick spots, so far as I have examined
them, always contain fully grown in-
sects.
The first published intimation that
these spots on Aster and Solidayo are
not simply insect galls or simply fungi, that I have noticed. is by Mr. W. R.
Gera~d,~ who, doubting their fungoid
nature, sent specimens to Mr. C. V.
Riley, and was told that (at least so far as the forms on Solidago are concerned)
they are the galls of C. carbomfera,
Professor C. H. Peck also makes a sim-
ilar statement in one of his later reports on New York fungi.6 Interested in the
subject by these notes, I have examined
5 Bulletin Torrey bot. club,
Oct. 1876, v. 6. p. 114
[PSYCHE, Rec., no. 24041.
tj 29 Kept. N. Y. ah'. nut. hist., p. 31.



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200 PSYCHE. [ Aiigust-September 1884.
a large number of specimens from dif-
ferent parts of the co~intry, and without exception have demonstrated their com-
posite nature.
This compound character of the galls
implies a close interdependence between
the fungus and insect. That Rhytisma
solidaginis or R. asteris cannot occur
without the presence of Cecidomyia
ca?-bomyera, or vice versa, cannot be
said ; yet I have never seen one without the other. Only a study of the develop-
ment of the galls can show whether the
insect paves the way for the fungus or
lives only in leaves previously attacked by the latter ; but the great powers of
multiplication and dissemination pos-
sessed by most fungi incline me to the
belief that the former is the case, the
mycelium being unable to penetrate the
uninjured plant, as Hartig has shown to
be the case with parasitic species of
Nectria, etc. From the carbonization
of all the species of Rhytisma, it is pi-ob- able that the color of the galls in the
present instance is due to the fungus.
The form of fruit of the Rhytisma,
and the early development of the galls,
could be easily made out by any collect- ing entomologist or botanist living in the eastern states, where they occur ; and as I no longer have access to good material these notes are published in their pres- .
ent incomplete form to draw attention to a very interesting subject for further
study.'
7 Sections of an undetermined cecidomyid gall on Impatiens fdva, from Medford, Mass., prepared in my labaratory by Miss L. N. Martin, show a mycelium somewhat similar to that noticed in Aster and Solidago leaves, and there is also a certain amount of carboniza- tion. It will be interesting to observe whether the mycelium is always present in this g-:ill which is not uncommon.
WANT OF SYMMETRY AMONG INSECTS.
BY OSKAR PAUL KRANCHER, LEIPZIG, GERMANY, The extraordinary symmetry which
occurs among insects is usually brought
prominently forward in most of the
books which treat of entomology.
Noth-
ing is pictured more symmetrically than, for instance, the str~~ctures of bees and ants, or the color' of butterflies, which latter is prominently reputed to have a
perfectly symmetrical bilateral equality. Although there is much truth at the bot- torn of all this, although nature in many cases works with great symmetry. yet
it must not be overlooked that even this symmetry is often converted into its
strict opposite. Surely no observing
lepidopterologist hlis failed to notice
that the coloiation of the wings of his
favorites is to be recognized as strictly symmetrical only in the smallest num-
ber of cases. that, indeed, that of one
side, which certainly resembles that of
the other in its superficial aspect, still shows many differences in its details,
and there is little foundation for assert- ing- that they are symmetrical.
I might
cite inniimerable examples of this. but
the reader can better see them for him-
self. This is most plainly shown in the




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