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C578
ENT

CIRCULAR NO. 19, SECOND SERIES. [2D ED.]

United States Department of Agriculture,

DIVISION OF ENTOMOLOGY.

THE CLOVER MITE.
(Bryobia pratensis Garman.)
CHARACTERISTICS AND METHOD OF WORK.

The subject of this circular is a reddish-brown mite about twice the
size of the ordinary red mite affecting greenhouse plants. It is about
three-hundredths of an inch in length, oval, and with remarkably long
anterior legs. Other structural features, together with the peculiar
hairs which clothe different parts of the body, are illustrated in the
accompanying figure, which represents, much enlarged, the full-grown
mite, viewed from above and from below.

This mite first came into special prominence as a disagreeable invader
of dwelling houses about ten years since, but it had been known for a
number of years earlier as an enemy of various fruit and shade trees
and forage plants, its occurrence on clover, particularly in the Middle
States, being indicated in its scientific name, pratensis, and its com-
mon name of clover mite. It belongs to the family of vegetable-
feeding mites, Tetranychide, which includes such well-known depre-
dators as the red spider of greenhouses, already referred to, and the
six-spotted mite, which is quite troublesome to oranges in Florida.
In California, where this plant mite is especially mischievous, it has
been very generally confounded with the red spider, and in probably
most. of the references to injury to deciduous trees on the Pacific Coast
by the “red spider’’ the real culprit is the insect under discussion.

The presence of this mite on foliage, either of clover or trees, causes
the leaves to yellow, or assume a sickly appearance, as if attacked by
afungus. On the tender leaves of clover, notably on the upper side,
the juices are extracted, often over irregular, winding areas, imitat-
ing in appearance the burrows of certain leaf-mining larve. The
most notable indication, however, of the presence of the mite is the

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occurrence of the eggs massed often in such numbers as to completely
cover the bark at the crotches and branches and sometimes over the
entire surface of the trunk. These eggs are of rather large size, of a
reddish color, and are conspicuous objects. When numerous the
decided color they impart to the bark leads to their ready discovery.

As out-of-door enemies they are injurious at times to clover and
other grasses, including the true grasses, as blue stem, but it is to fruit
trees that their injuries are especially marked. Throughout the Pacific
Coast and in the fruit districts of Colorado and other Western mountain
States the clover mite is one of the principal enemies of such deciduous
fruits as peach. prune, plum, apple, pear, almond, cherry, etc., and the
poplar and elm, black locust, arborvite, etc., among shade trees. As
house pests they are troublesome from their presence merely in their
efforts in the fall to find safe hibernating quarters and occasionally in
their spring migrations in search of suitable breeding grounds.

ORIGIN AND DISTRIBUTION.

Attention was first drawn to this mite in 1879 at Washington, D. C.,
from its occurrence on the trees in the Department grounds and also
on clover on lawns. It has since been reported from numerous locali-
ties from Massachusetts to California. Northward it occurs in the Kast
in northern New York and Canada. East of the Mississippi it has not
been reported in the southern tier of States, the southernmost records
occurring in Tennessee and North Carolina.

On the Pacific Coast it is known from San Diego, Cal., to East
Sound, Washington; and at Las Cruces, N. Mex., it is a serious fruit
pest. In the Sierra Nevada Mountains in California and in the Rocky
Mountains in Montana it has been found at elevations of from 7,000 to
8,000 feet.

It is remarkable, therefore, for its ability to exist under marked
differences of temperature and elevation. Its wide distribution and
its occurrence in situations remote from settlement indicate that it is
a native species. It was first characterized scientifically by H. Garman
in 1885, who proposed for it the common and Latin name by which it
is now known.

HABITS AND LIFE HISTORY.

The wide range of this insect and the different climatic conditions
under which it exists lead, as might be expected, to certain variations
in its hfe history and habits in different localities. In the more
northern regions of its occurrence and in the higher elevations it win-
ters in the egg state, the last brood, if it may be so, called, maturing
in the fall, and depositing eggs on branches and trunks of trees some-
times in sufficient numbers to entirely cover the bark two or three
layers deep. In 1889 we received a mass of these eggs several layers

deep on a piece of bark which the sender states was from an area of at
least 50 square feet of eggs on the south side of trunks of cottonwoods
growing at an elevation of from 6,000 to 8,000 feet. This was in the
Sierra Nevada Mountains, Tuolumne County, Cal., and we have had

a similar account, with
specimens, from McCar-
thy Mountain, in Mon-
tana, at about the same
elevation. In the Mid-
dle and Eastern States,
where the eggs are fre-
quently found on fruit
trees, they are usually
confined to the crotches
and branches and are
not nearly so abundant.

In the colder regions,
where the winter’ is
passed in the egg state,
the issuance of the young
mites the following
spring varies from May
until the middle of June,
depending on the char-
acter of the season. In
the warmer regions—as,
for instance, in the lati-
tude of Washington,
D. C.—the mites begin
to be noticeable on foli-
age and grass in May or
earlier, and enter their
hibernating quarters
early in October, in crev-
ices of fences or walls,
or under the loose bark
of various trees. It is
seen, therefore, that in
the warmer localities
breeding is hardly inter-
rupted during the win-

Fic. 1.—Bryobia pratensis: a, dorsal view; b, ventral
view; c andd, claw; e, f, g, mouth parts; h, i, j, body
seales; k, l, m, leg spines (from Insect Life).

ter months and the winter is passed quite as much in the active as in
the egg state. Throughout the summer young are produced continu-
ously, as with most other plant mites, with no particular differentiation

of broods.

AAA i
en
The habit of this mite of abandoning its feeding situations in the
fall to seek hibernating quarters elsewhere leads to its being a house
pest of no mean importance. This is particularly true wherever it
has been breeding on clover or other grasses near dwellings. From
such situations, particularly in the Mississippi Valley States, it often
swarms into dwellings through doors or windows, its small size ena-
bling it to penetrate wire screens with ease, to the very considerable dis-
quietude of the housekeeper. There are only a few records of their
entering houses in the East, and in the extreme West they seem only
to have been found on trees.

REMEDIES AND PREVENTIVES.

The protection of fruit trees from the attacks of this mite is com-
paratively easy where the winter is chiefly passed in the egg state, as
in Colorado and other elevated or cold districts. The experience of
Mr. C. P. Gillette in Colorado has shown that the eggs may be very
easily destroyed during the winter by applying kerosene emulsion to
the trees at about twice the ordinary strength, viz, diluted with five
parts of water. Spraying at this time is both economical and easy,
on account of the absence of foliage, and no danger will result to the
plants from the application. Such an application also in the warmer
latitudes will be of almost equal value as a protection to fruit trees,
since it will reach what eggs there may be and also many of the mites
secreted in the cracks of the bark.

It is a much more difficult matter to protect clover and other grasses
from the mites, except as it may be possible to spray in winter the
trees, fences, etc., on or in which the mites may be hibernating, in the
vicinity of lawns.

Their entrance into houses in the fall may be prevented by spraying
the lower portion of the building, walls, ete., with pure kerosene as
often as need be and also spraying the lawns immediately about the
building with kerosene emulsion nine times diluted. The mites may
be destroyed after they have gained entrance to the house by the free
use of buhach or pyrethrum powder, burning brimstone, or spraying
with benzine, taking due precautions with the latter substance in the
matter of fire.

C. L. MARLATT,
First Assistant Entomologist.
Approved:
JAMES WILSON,
Secretary of Agriculture.

WASHINGTON, D. C., July 19, 1897.

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