This paper is primarily an attempt to present adequate descriptions
of the types of 30 itonid (cecidomyid) and 2 eriophyid (mite) galls,
collected by the writer on hickory leaves. It is believed to contain
sufficient new material to warrant its publication in advance of a
general survey of N. E. United States zoocecidia, of which it will form
a part. The data is based on collections made in Connecticut, Ohio and
Kansas, most of the material however, being taken in Ohio.
In addition, those forms (few in number) previously described which
have not been seen by the author, have been added, so as to give a
character of completeness to the survey of the two groups of galls.
There are three groups of zoocecidia occurring on hickory trees:
1. Galls formed by species of Eriophyes (Fam. Eriophyidæ of
the Acarina or mites), or an allied genus. Only two are known.
2. Galls induced by species of Phylloxera (Aphididæ of the
Hemiptera). Pergande[2] has presented an excellent survey
of these insects accompanied by very satisfactory descriptions
of the cecidia formed by them.
3. Galls caused by species of Caryomyia (Itonididæ of the
Diptera). Possibly other genera may be represented on the
hickories, but according to Felt[3] “most of the hickory leaf
galls are probably made by species of Caryomyia, though
other midges have been reared from these deformities.”
The genus Caryomyia, which undoubtedly occupies an important place in
relation to the majority of the galls described in the present paper,
will be given special consideration. Felt, to whom American cecidology
is heavily indebted for his extensive studies of dipterous cecidozoons,
presents the following description of the genus Caryomyia in the same
citation as that immediately above.
“Allied to Hormomyia, but differing by the thorax not being greatly
produced over the head and by the presence of but 14 antennal
segments. The males may have the flagellate antennal segments binodose
or cylindric and subsessile and invariably with three low, stout
circumfili. The antennal segments of the female are cylindric and with
two circumfili; palpi tri- or quadri-articulate; wings rather broad,
the third vein joining the costa at or near the wing apex; claws
simple, the pulvilli well developed. The ovipositor of the female is
short and with minute lobes apically. The genus appears to be confined
to hickory leaf galls.”
Adult insects not technically known are given the old generic name
“Cecidomyia.”
These galls as well as similar ones on other kinds of plants arise as
the result of some stimulus (the nature of which is still not definitely
known) applied by the very young larva to the growing tissue of the
immature leaf. Nothing has yet been done on the development of the
itonid galls of the hickories, but from studies on very similar types
we have reason to believe that the ontogeny of the itonid forms is
as follows: The egg is probably deposited superficially (for the
ovipositor of the female Caryomyia is short) on the under side of the
leaflet; on the upper side in a few cases.
Hyperplasia or excessive cell proliferation results (probably not
until after the larva has emerged from the egg) forming at first a
saucer-shaped structure, then cup-shaped and finally by the ingrowth
of the edges, the gall becomes a closed structure enveloping the larva
in a chamber. The distal growth, seldom if ever in the hickory forms,
proceeds so far as to obliterate the opening which was so prominent in
the very immature cup-shape stage. Hence in practically all galls of
this type a minute canal or pore can be demonstrated at the distal end.
In Küster’s[4] very serviceable classification of abnormal plant parts,
these fall under his “umwallungen” cecidia, a term very succinctly
describing their mode of development.
Two of the following described galls have been studied histologically
by Cook,[5] _Caryomyia holotricha_ O. S. and _C. tubicola_ O. S.
Concerning the problem of the distribution of the galls on the
different species of hickory, it is still too early to be able to make
any positive assertions. In most of the reports the species of tree has
not been given. It is very well known that certain species of galls are
found on 2 and 3 species of hickory, but whether they are developed on
all indiscriminately is not known. _H. cordiformis_ seems to bear much
fewer species than _H. ovata_ or _H. alba_. In the present list, the
report of the gall upon a particular species of tree does not at all
imply that it does not occur on others.
Having had the opportunity to give attention to gall collecting
in three rather widely separate localities, eastern Connecticut,
southern and northern Ohio and eastern Kansas, some observations on
the geographical distributions of the hickory itonids are here briefly
presented.
It is sometimes stated that the distribution of gall insects is similar
to that of their host plants. In certain cases this does not seem to
be true. In that of my number 32 first found and described by Sears,
no report of this large and striking form has appeared, showing it
to occur east of the Allegheny mountain system, a region in which
_H. ovata_ is abundant. In the cases of my numbers 5, 9, 19 and 31,
all heretofore unreported and possessing prominent distinguishing
characters, it would seem as though they were somewhat restricted in
their distribution, for while comparatively common in Ohio, they are
never seen in Connecticut or Kansas, where equally intensive collecting
was prosecuted. So few are the students of cecidia and so meager
the data in this field, that it is, however, much too early to make
positive assertions in matters of geographic distribution.
The data on the galls presented herewith was compiled for the most
part at the time of collection; the notes and drawings made from fresh
material. For later comparative work, the material was all preserved in
formalin, each collection being assigned to a vial.
The writer has refrained from attaching a specific name to his new
species of cecidia, a practice very common on the part of European
cecidologists. Even though the adult gall has no direct relation to
the adult insect, the fact, nevertheless, remains that the specificity
of the gall owes its origin to the specificity of the physiological
phenomena of the larval insect, and it is this, which in the mind of
the writer, gives pre-eminence to the insect. The adult gall and the
adult insect can be conceived as arising from the same complex, the
larva, the adult insect bearing, however, a more intimate and direct
relation to the original source of events than the gall. In many cases
the adult insects offer characters, making possible the delimitation of
species, with greater exactness, than do the galls. For these reasons
new names of cecidia should only appear with adequate descriptions of
the cecidozoons.
Though the galls almost uniformly occur on the under side of the
leaflet, the drawings have presented them in an inverted position, with
the gall uppermost, this being the position in which the galls would be
examined. In practically all cases there are two sketches of the type,
one showing the exterior aspect of the gall, the other the interior as
seen in a vertical, median section. The figure number is in all cases
the same as the list number.
The writer wishes to express his appreciation of the hospitality of
his friend, J. L. King, who, as assistant entomologist for the Ohio
Experiment Station, shared his field laboratory during some of the time
in which cecidological collecting was being carried on.
Though the writer has seen (with a few exceptions) the types herewith
detailed an amply sufficient number of times to establish them as
types, he does not claim infallibility, for the key he has worked
out to these types. It is hoped, however, that it, together with the
descriptions and illustrations will enable the student of the hickory
galls to become better acquainted with the members of the two groups
treated.
Britton and Brown’s Illustrated Flora Northern U. S. and Canada, (2nd
edition), New York, 1913, has been followed in the matter of plant
nomenclature.
The following two galls whose makers have been named by Felt have
probably not been seen by the writer. Felt’s descriptions are given.
They are not included in the key.
=Caryomyia thompsoni= Felt.
“Globose, thin-walled, long haired, melon-shaped, dia. 2-3 mm.”
See my number 23.
=Caryomyia antennata= Felt.
“Globose, thick-walled, yellowish green or brown. Dia. 4-5 mm.”
This description, as far as it goes, would indicate a similarity to
C. persicoides Beut.
Felt, Jour. Econ. Ent. 4:456. 1911.