Savory - Arachnida 1977

250 IV. DE ARACHNOLOGIA
Although the tiny Tarsonemidae are known to include plant-feeding,
fungus-feeding and insect-feeding species, perhaps the most important
are Po!yphagotarsonemus latus, the broad mite and Stenotarsonemus pallidus,
the cyclamen mite. The former as the generic name implies feeds on and
injures many different kinds of plants. In the Americas it is known to
damage citrus both in glasshouses and in groves. The latter, despite its
common name, probably achieves greatest importance for the damage
it produces on glasshouse and field-grown strawberries. It should also be
mentioned that tarsonemids of the genus I ponemus feed on bark beetle
eggs, live as commensals in the galleries and transport themselves
(phoresy) from gallery to gallery on the adult beetles.
Among the Eriophyidae, the rust, bud and gall mites, the genus
Eriophyes contains a very large number of species, all of which are
plant parasites. These curious creatures are barely 0·1 mm long, and
invisible to the naked eye. The tropicopolitan citrus rust mite, Phyllocoptruta
oleivora, is perhaps the best known and most important of the
russet-producing species. It produces a mild to severe russeting or sharkskinning
of citrus fruits throughout the world, is often responsible for
small, early-maturing fruit and has been implicated in the transmission
of citrus greasy spot. Many other russet-producing species are known,
among them the apple rust mite, Aculus schlectendali, and the pear
blister mite, Eriophyes pyri. The latter is well known as a pest all over
England, Europe and America for its attacks on pear, apple and rowan.
Leaves of infested trees open in the spring with small yellow or dark
green spots that soon turn brown; the leaves then blacken and die. This
is caused by mites which have wintered under the bud scales and burrowed
into the leaves where they lay their eggs. The hatching young
then spread the trouble by burrowing throughout the leaves and into
other leaves. This is continued for the entire summer but before the
leaves fall the mite is safely hidden in a bud for wintering.
There are also many bud and gall mites. Among them, in western
North America, is the citrus bud mite, Aceria sheldoni, which causes
serious abortion and loss of buds on lemon trees. In Great Britain, the
species which most frequently demands the attention of fruit growers is
the blackcurrant gall mite, Cecidophyopsis ribis, which is now also widespread
in Europe and Canada. It produces "big bud" in blackcurrants
and also attacks white- and redcurrants, flowering-currants and gooseberries.
The presence of the parasite causes the buds to swell to almost
double their normal size and die in the early weeks of summer. Red- and
whitecurrant buds swell only if the infestation is particularly severe but
they also die. Gooseberry leaves are often attacked and are undersized
and yellowish. This mite can only be found by microscopic examination
of parasitized buds between July and March when the mites are living
30. ECONOMIC ARACHNOLOGY 251
and depositing eggs in the bud tissues. On the death of the bud, the mites
move to t~e le~ves and_ on_ bright days when a slight wind is stirring
attempt migratiOn by chngmg to the legs of passing insects or springing
upwards to be blown on the wind as aerial plankton. During heavy
migrations, many thousands of individuals leave a bud in a day and
little bunches of a hundred mites together may be seen rolling out of the
buds on to the leaves below.
Blackcurrant is also attacked by two other gall mites. Ph)'llocoptes
masseei and Ox)'pleurites neglectus, but these, although disfiguring, are
not responsible for great damage.
Reference should also be made here to the large number of species of
the extensive genus Eriophyes which are responsible for the formation of
the apparently innocuous galls on many plants, including trees, shrubs
and herbs. Mite-galls can be distinguished from insect-galls by a natural
aperture through which the mites can escape. Mite-galls are also gene~ally
covered_ with a felty mass of "hairs" produced by the abnormally
stimulated epidermal cells of the plant. l\lites in the middle of this
dense mass are often difficult or nearly impossible to detect. Examples of
common mite-galls are the red growths seen on sycamore leaves, the
round red galls on alder, the "nail galls" on lime trees and the galls on
lichens of the genus Ramalina. The "witches brooms" or bundles of
small twigs on the branches of birch, hackberry and other trees are
appa:ent~y the result of a symbiosis bet\veen mites and fungi. Interesting
as this widespread mite-gall parasitism is, it cannot claim more than
passing mention, since its economic influence is insignificant.
One would also be remiss not to mention here the acarid, Rhizog!yphus
echinopus, commonly known as the bulb mite. This species either
causes damage or compounds insect and fungus damage to narcissus,
jonquil, tulip, lily and similar plant bulbs. Mites of the family Acaridae
~re normally thought of as feeders on dying or dead plant and animal
tissues, stored crops and manufactured produce, but the bulb mite
apparently may cause primary as well as secondary injury.
Mites of the super-family Acaroidea including the families Acaridae,
Carpoglyphidae and Glycyphagidae are perhaps our most important
house and factory mite pests of stored agricultural crops and manufactured
products. The cheese mites are undoubtedly the first to demand
attention. Several species of mites may be found feeding on cheeses in
factory, warehouse and home; Acarus siro, Tyrophagus longior and Tpophagus
putrescentiae are three. Two or more species may often be found
feeding and living together. Besides cheeses, these mites are able to live
on many other stored and manufactured products such as hams bacon
stored grains, breakfast cereals, flour and dried milk. They also ' feed on '
dead insects and the media of insect cultures.