Red
Palm Weevil (RPW) Rhynchophorus ferrugineus, a concealed tissue borer is
a lethal pest of palms and is reported to attack 17 palm species worldwide. It
is a large insect about >25 mm long, polyphagous and attacks a broad range
of palm species, causing severe damage to the affected crop. It is quite easy
to distinguish RPW from other insects as it has a distinct dark red color with
black spots appear on its thorax. It also has wings with strong flight ability
that reaches up to 50 km in distance within 24 hours of a time range. This
ability further contributes to the RPW widespread in palm plantations. Male and
female RPW can be differentiated based on the physiological appearance of its
rostrum in which male has slightly crooked and hairy rostrum compared to female
RPW. Meanwhile, female RPW is equipped with straight and longer rostrum that
enable it to poke a hole in palm trees to oviposit. RPW were able to lay
approximately 270-396 eggs per female. The number of eggs laid would decrease
day by day over a period of 11 weeks. After the 11th weeks, female
RPW could not lay any more eggs until death although the male still mates with
the female. After 2-5 days, an average 43.5%-75.9% eggs would successfully
hatch. The larvae then bore into the interior part of the palm and feed on the
soft succulent tissues of the palm. Then, the larvae would develop into a
non-feeding prepupal larvae stage. At this stage, the prepupal larvae construct
an oval-shaped cocoon made of fibre and pupate inside the cocoon, developing
into adults. The life cycle range from 82-139 days depending on the different
geographical region of the world. There are about 3 to 4 generations of RPW
throughout the year.
Figure 1: Red Palm Weevil
Geographical
distribution of RPW includes most countries in the Middle East and Southeast
Asia, particularly coastal areas due to the availability of its favourite diet
which is coconut trees. Originating from the Middle East, a mass outbreak of
RPW infestation was first reported at the United Arab Emirates in 1986 and
slowly started to spread to other continents via transportation of infected
palm trees to outside of the country. These transported palm trees serve for
the purpose of ornamental value or as logs for the manufacturing industry. RPW
is considered more as a threatening pest in the Middle East and Southeast Asia
compared to Europe due to these two reasons, which are RPW prefer a country
with hotter climate over the alternate seasonal country and palm trees are a
vital source of economy for some countries in the Middle East and Southeast
Asia. This includes the date palm tree in Saudi Arabia and oil palm tree in
Malaysia. Based on the Malaysia Department of Agriculture, RPW was first
introduced to Malaysia from Thailand via illegal transportation of infested
logs. These logs escaped clarification by the Royal Malaysian Customs
Department and further spread RPW infestation to Malaysia as a result of some
industrial corporates’ negligence.
In
Malaysia, RPW is the key pest of coconut, Cocos nucifera. This pest was
first detected by the Department of Agriculture in 2007 in all seven districts
in Terengganu. In 2016, RPW has been reported to hit five other states
including Perlis, Kedah, Pulau Pinang, Terengganu, and Kelantan. RPW has been
reported to mostly attack young palms i.e. age below 20 years. There are three
ways that RPW attack the coconut palms (1) through the shoot and straight to
the cabbage of the coconut (2) adult make a hole through the trunk or use holes
that are made by other insects (3) adult RPW digs the soil and tunnelled into
the coconut palm root system. In coconut, damage due to the Rhinoceros beetle
Oryctes spp. and the diseases of frond rot and bud rot may predispose the RPW
females to oviposit into the palm. Although RPW’s preference of diet is now
mainly focused on coconut trees, there is a high probability that it will
switch to the more economically significant oil palm tree in the near future
due to its polyphagous feeding habit. Therefore, it is very crucial for the
Malaysia government to tackle this issue before it worsens. The major
components of the RPW-IPM programme currently being used in coconut are
monitoring, palm and field sanitation, trapping of adults using food baits,
preventive chemical treatments of wounds, treatment of palms infected with bud
rot disease or infested with Oryctes to prevent attraction of RPW adults, filling
fronts axils of young palms with a mixture of insecticide and sand, curative
treatment of infested palms in the early stages of attack, eradicating severely
infested palms, cutting fronds if required at a distance of 1 m from the frond
base, and educating and training farmers and agricultural officers.
The
severely infested coconut palms showed signs of wilting, drooping of dried
leaves like an umbrella-shaped, skirting-shaped leaves or collapsed crown.
Other symptoms for heavily infested coconut tree are the presence of borer hole
and brown discoloration at the junction of coconut frond and stem. Besides
that, the RPW infested tree also shows audible symptoms which is the sound of
crunching and sucking noise made by RPW larvae eating away the tree’s inner
stem. Oftentimes, it is already too late to save the coconut tree when one of
the symptoms is detected. This is due to its hidden tissue borer nature that
cannot be seen from outside. Although the RPW-IPM programme has taken place in
Malaysia for several years now, the progressive effects of its action are yet
to be seen as more coconut trees are being infected. A more intensive and
specific RPW eradication method should take place in order to outmatch the
fast-growing RPW pest infestation. Many groups of scientists have suggested a
few eradication techniques specifically for RPW, however its application to the
field is not yet popularized. One of the many techniques suggested was acoustic
signal detection of RPW larvae boring inside tree trunks by using off-the-shelf
recording devices. The device applied mathematical algorithms method such as
Gaussian mixture modelling in order to accurately separate RPW larvae boring
sounds from background noises. The idea was made to detect early phase RPW
infestation in which the coconut trees have not fully damaged yet and thus
enabling its salvation. Aside from this device, a biological control method
with specific target against RPW has also been suggested by a few
entomologists. One of them is the use of nematode (Steinernema carpocapsae)
against all stages of RPW with efficacies up to 80% and above. While biological
control agent has long been used in integrated pest management, a more peculiar
suggestion is the use of dogs in Red Palm Weevil detection by a team of
scientist from Middle East country. They claimed that high olfactory sensory
level in dogs would enable them to smell the unique signatures of chemical
compounds produced by plant-feeding insects. This theory has already been
proven in the use of German Shepherds to locate gypsy moth and yet to be
explored in their ability to detect RPW pest infestation.
Aside from being palm trees pest,
RPW larvae are also known for being a scrumptious delicacy in some Southeast
Asian countries such as Vietnam, Eastern of Indonesia, Malaysian Borneo, and
Papua New Guinea. The chubby larvae are also called as sago worms and often
prepared with sago flour, fish sauce, porridge, salad, or sticky rice. The
taste of RPW larvae was described as creamy and juicy when eaten raw and
meat-like when roasted. Here in Malaysia, RPW larvae are known as ‘butod’ by
Sabahan people and can be sell as much as RM40 to RM 45 per kilogram. Although
insects particularly pest was constantly associated with hygiene issue, it is
not quite true for ‘butod’ as it is only known to feed on and live inside the
sago palm pith since it hatched. Besides that, it is also considered an
important source of protein for the people in the South of New Guinea where the
food source is scarce.
