Bt Research 2015, Vol.6 No.2 1-10
ISSN 1925-1939
2
(Moore et al., 1987). Once the mite has invaded an
inflorescence of a coconut, it can spread to adjacent
ones through continuous migration by walking. Rapid
spread from plantation to plantation and coconut belts
are mainly performed through wind, especially during
dry season (Haq, 2001). This mite has established the
status of a serious pest of coconut in Kerala and other
States of peninsular India and neighboring islands
(Haq et al., 2002). Rapid invasion, colonization and
extensive damage caused by this mite in the coconut
belts of India have created serious concerns across the
society. Accordingly, much effort has been made to
control this pest.
Being microscopic in size and with cryptic habitat,
A.
guerreronis
can reach places that are small enough to
be inaccessible to their predators, and they find partial
refuge beneath the perianth (cap on the top) of the
developing coconut buttons (Haq, 2001). However,
some predators can penetrate beneath the perianth of
the coconut fruits, and attack the coconut mite. The
predatory mites phytoseiidae family, like
Neoseiulus
baraki
(Athias-Henriot) and
N. paspalivorus
(De Leon)
were found prey on
A. guerreronis
(Reis et al., 2008;
Aratchige et al., 2007).
Hirsutella thompsonii
Pat.
(Hypocreales: Ophiocordycipitaceae), a fungus was
also found to have some entomopathogenic effects on
A. guerreronis
(Fernando et al., 2007). Nevertheless,
no effective solution is reported yet to combat
A.
guerreronis
attacking coconut palms. Strains of
Bacillus thuringiensis
(
Bt
)
(Zhou et al., 2014) have
been proven as the most applicable biological agent in
combating a wide number of insect pests (Fadeland
Sabour 2002). However, application of any strain or
subspecies of
Bt
to combat
A. guerreronis
has not
been reported. Under these circumstances, this study
addresses the following questions: (a) whether
Bt
subspecies
kurstaki
is efficient to successfully combat
A. guerreronis;
(b) if the answer is ‘yes’, how this
biopesticide would be applied to the coconut palm;
and (c) how this biopesticide would be produced at a
cheaper rate affordable to the farmers in countries
where this tree is grown predominantly.
Results
Handling of
A. guerreronis
is highly risky as it is
much sensitive to moisture and exposure to air. In
addition to this, since these mites are microscopic and
healthy ones are actively moving on the meristematic
region of the button within the glass ring, it was very
difficult to manage them for counting and
photographing. Due to their high sensitivity to
moisture, the feed was administered as fine powder
with no adhesives. Compared to pellet from LB
control, the starchy substrate (due to potato flour) in
the potato flour supplemented sample helped the fine
powder stick firmly to the buttons, even in the absence
of moisture.
Collection of coconut buttons
The coconut palm was affected by
A. guerreronis
with
tender nuts showing different stages of infestation
with characteristics injuries
i.e
., triangular creamy
white V-marks on the tender nuts (Fig. 1). One month
old coconut buttons were collected to culture the mites
at the laboratory conditions, providing suitable
temperature and humidity (Fig. 2). The average area
of the buttons (perianth region) used in this study was
about 8.6 cm
2
and diameter 3.23 cm; because
A.
guerreronis
only harbors on this meristematic region
(protected by the perianth), sucking the juice.
Life cycle of mites
The life cycle of this mite includes egg, two larval
instars and an adult stage, which span about 9-10 days
(Fig. 3). The longevity of adult stage was between 3 to
5 days. The pale colored and worm-like elongated
adults with two pairs of legs on anterior part of the
body are microscopic, measure 200-250 µm in length
and 35-50 µm in width. Both nymphs and adults cause
injuries on the nut. Each female can lay approximately
30-50 eggs, which are shiny, white and globular in
shape. It hatches into larvae (protonymph) in three
days. The second instar larva (the so-called nymph)
subsequently moults into adults. The populations
beneath the perianth of a developing coconut fruit
build up rapidly, often producing thousands of mites
in each of several aggregations on the same fruit.
Massive populations of coconut mites may be present
beneath the tepals, the individual parts (tepal) of
perianth and on the fruit surface beneath the perianth
for about six months during the development of the
nut (it takes about one year for a nut to mature), after
which the populations decline.
