Agriculture Reference
In-Depth Information
Mites
Mites form a subclass, known as the Acari,
within the class Arachnida (phylum
Arthropoda). The Arachnida also includes, for
example, harvestmen (subclass Opiliones),
spiders (subclass Araneida) and scorpions (sub-
class Scorpionida).
EXTERNAL FEATURES
Members of the Acari are minute or small arach-
nids and, although sharing many features of
insects, usually lack obvious body segmentation.
Unlike insects, mites have no antennae, com-
pound eyes or wings; also, the body of a mite
is composed of just two main sections: a
gnathosoma (which bears a pair of segmented
pedipalps and the mouthparts - including,
ventrally, a beak-like hypostome) and a sac-like
idiosoma (which bears the legs).
The pedipalps have up to five main segments:
trochanter, femur, genu, tibia, tarsus, the tarsal
segment often bearing at its basal inner angle
an articulating, two-, three- or four-pronged
sixth segment called the apotele
(Fig. 164).
The
mouthparts of mites are adapted for biting
or piercing and usually include a pair of, often
chelate (for grasping) or needle-like (for pierc-
ing), chelicerae; the chelicerae often terminate in
one fixed and one moveable, thumb-like digit,
and often coalesce to form a needle-like
stylophore.
Adult mites, unlike insects, are usually 8-
legged, and each leg has up to six segments: coxa,
trochanter, femur, genu, tibia and tarsus
(Fig.
165);
also, the legs often end in a soft
ambulacrum (which may comprise a pretarsus
and a pad-like pulvillus), at the tip of which may
Fig. 164
Segmentation of the pedipalp of a mite.
Fig. 165
Segmentation of the leg of a mite.