Savory - Arachnida 1977

256 IV. DE ARAGHNOLOGIA
are involved, the is also known as piraplasmosis or babesiasis.
As might be expected with such a widespread, multiple-host multiplepathogen
disease, several ticks of the genera Boophilus, Dermacentor
and Ixodes are also known to be vectors. Related important animal
diseases of the eastern hemisphere, of which the best known is east coast
fever of cattle, are also caused by tick-borne, protozoan parasites of the
genera Theileria, Gonderia and Cytauxzoon.
Psoroptid mites can be important economic pests of their mammalian
hosts. Members of the genus Psoroptes are ectodermal parasites of
cattle, goats, horses, sheep and several non-domesticated animals; the
species that produces mange on sheep may produce death. Dogs and
cats are often attacked by the ear mite, Otodectes cynotis, heavy infestations
of which result in fever and depression. Chorioptes species produce
chorioptic mange at the base of the tails and on the legs of cattle, goats,
horses and sheep, intensely irritating the animals.
The pyemotid, Pyemotes ventricosus, not only causes "grain-itch"
among granary and cereal crop workers but may also complicate the
natural control of stored grain pests and has been reported living within
corn stalks. "Grain-itch" is a severe, eruptive dermatitis of grain handlers
that can be quite irritating. Also, the mites are known to be parasites
oflarval and pupal Lepidoptera, and so may aid in the control of
certain stored products pests. At the same time, they are also known to
feed on parasitic wasps and thus may reduce natural control of certain
pests. Since the mite has also been recorded from corn stalks, where it
was apparently feeding on the plant juices, the could be parasitic
on the crop, could increase or decrease natural control of other pests,
and finally complicate harvesting.
Certain Pyroglyphidae, particularly those of the genus Dermatophagoides
are commonly found in house dust. One D. pteronyssinus,
has been implicated as causal agent of house dust allergy, and was
indicted as the cause of an irritating nasal and scalp disorder.
Rather more serious are the sarcoptic "scab mites or itch mites" of
the genus Sarcoptes. The well-known Sarcoptes scabiei is the cause of
human scabies, a dermatitis recognized by scabby, itching lesions that
may persist for some time. Females, minute grey, tortoise-like mites,
about 330 to 450 ,urn long, produce the lesions by burrowing under the
skin in soft moist areas between the fingers and toes, around the knees,
elbows and wrists and around the pelvis and buttocks. Scabies is often
highly contagious in areas of high population density. Several similar
mites, other races or other species of the same genus, are responsible for
scabies of domestic animals such as pigs, sheep, dogs and cats. Sarcoptic
mange of pigs and dogs can be particularly severe, debilitating or lethal.
The so-called "harvest mite" or chigger is perhaps the best known of
30. ECONOMIC ARACHNOLOGY 257
all the mites that are parasitic on man. Trombiculid mites of several
genera cause the \vell-known welt-like dermatitis or "trombidiosus"
of chigger attacks. In the whole of Europe, the species most frequently
involved is Trombicula autumnalis: in North America, species of Eutrombicula
are most frequently indicted. Adult Trombiculidae are predatory
on other arthropods and are most commonly found on or in the
soil; it is the six-legged larva that is parasitic on vertebrates, including
man. Before the true relationship of the larvae and adults were known,
the larvae were often described under separate names. The pink to
bright red welts with a central feeding tube or "stylostome" at the point
of the chigger attachment is characteristic of chigger attacks. However,
the amount of irritation produced by chiggers varies; some people have
little or no symptoms, vvhereas others may even run a fever. These
mites and other genera of the family also attack other mammals, as well
as birds, reptiles and amphibians.
Before concluding this discussion on the economic importance of
mites it should be pointed out that the field of economic acarology is
relatively new when compared with that of economic entomology. In
fact, for many years the problem of controlling the limited known number
of economically important mites was considered within the province
of the economic entomologist. However, as mites have become better
known and the number of species has become more adequately differentiated
it has become evident that the study of acarology demanded a
special field of
To this end, there are today mite specialists,
taxonomic mite specialists of certain families and certain genera,
mite physiologists and even economic acarologists. Since this latter
expertise is rapidly growing and expanding it is no longer possible to
give simple control measures for economically important mites. The
reader is, therefore, referred to special economic treatises and texts on
mites for adequate up-to-date chemical control measures for the species
mentioned above.
The same applies to the so-called "biological or natural" control
measures. Less than 20 years ago, it \'>'as felt that few if any mites could
be considered to be beneficial to man and man's industries. Today a
number of species are known to be effective predators of pest mites and
pest insects and there can be no question but that many other beneficial
species will be discovered as the field of economic acarology grows to
become an important recognized scientific discipline.