Biology Reference
In-Depth Information
the main vector of KFD, by Bhat (1968) will remain classic in the field of ecology
of Indian ticks. The checklist published by Jagannath et al. (1973) and Miranpuri
and Naithani (1978) who reported 99 and 160 species, respectively, have helped
tick studies in India. The latest checklist is by Geevarghese et al. (1997), who have
reported 106 valid ticks after segregating the invalid species and synonyms from
the list provided by earlier workers. Other workers who have contributed to the tax-
onomic and biologic studies of ticks in India are Drs V. Dhanda, K.R.P. Singh,
Alwar, Heregoudar, Jagannath, Nagar, Gill, B.D. Sharma, Vazirani, etc. Most of
these workers have carried out studies on tick fauna in certain Indian regions where
they have been working.
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1.2 External Morphology of Ixodid Ticks
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The body of a tick is divisible into an anterior region,
gnathosoma
(capitulum),
and a posterior region called the
idiosoma
or the main body part. In the Ixodidae, a
sclerotized shield called the
scutum
covers the entire dorsal surface. However, in
the female, larvae, and nymph it covers only the anterior region. Scutum is absent
in Argasidae. There are a number of grooves on the scutum and these are named
after their location on the scutum, namely cervical, lateral, marginal grooves. The
scutal surface also may bear a number of small pits called
punctations
, which vary
in size and number. There are various other structures like ridges,
mammillae
, and
discs
on the dorsum of Argasidae. The posterior end of the idiosoma is divided into
a number of rectangular areas called
festoons
. These are absent in one genus of
Ixodidae, namely Boophilus and in all genera of Argasidae. Eyes when present are
situated on the lateral margins of the scutum, anteriorly in males or at the greatest
width of scutum in the female. In Argasidae if the eyes are present, they are situ-
ated on the lateral on the supracoxal folds. The adults of certain genera such as
Dermacentor and Amblyomma possess ornamental bodies, that is, some parts of the
scutum may have patches of enameled colors. Important structures placed on the
ventral side of the ticks are (1) v
entral plates
; (2)
genital aperture
placed anteri-
orly covered by a delicate sclerotized flap called the genital operculum; (3)
anus
on the posterior side; and (4)
spiracle
. The gnathosoma or capitulum consists of a
posterior basis capitulum to which is attached the mouthparts. On the dorsal surface
of basis capitulum in female ixodids, there is a pair of areas called porose areas in
certain species of hard ticks. Two spur-like structures called
corona
are situated
dorsally on either side of the posterolateral side of the basis capitulum. The mouth-
parts consist of a tonguelike projection called the
hypostome
over which lie dor-
sally a pair of chelicerae, which are used for piercing. Chelicerae consist of long
movable shafts and cutting digits attached dorsoanteriorly. Hypostomes possess a
number of rows of backwardly directed curved teeth, which vary in shape, size,
and number. The number of rows of teeth in the hypostome is a diagnostic feature
for ticks, for example, Amblyomma. There are two palps situated on each side of
the mouthparts. Each palp consists of four segments, that is, segment nos. 1, 2, 3,
and 4. Segment 2 is usually the longest one and may project basolaterally beyond
