Curbing Pink Mealybug (1997, Vol. 20 No. 4) - SIA
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Curbing Pink Mealybug (1997, Vol. 20 No. 4)
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CURBING PINK MEALYBUG
by
Trevor Falloon
The good news is that
cane is not its favorite food.
Even better news is that
it is hardly news anymore in a number of Caribbean islands where it was
wreaking havoc only a short while ago. So, for the farmer growing multiple
crops, anyone who enjoys puttering around the home garden or the lover of
greenery there is now little cause to be despondent.
The startling revelation
that the mealybug was attacking more than 125 different plants, later upgraded
to over 200, though essentially correct, needs to be reviewed in light of
current information.
The turn around from
predictions of doom can be credited largely to another insect, the Australian
ladybird, brought to the Caribbean and released to fight the mealybug. This
ladybird beetle, (Cryptolaemus montrouzieri) released in Trinidad,
Grenada and St. Kitts, just loves eating mealybugs and consumes many hundreds
in a few weeks. As a consequence, guango trees and various hibiscus plants that
were dying at one stage are today sprouting again. Indeed, one has to search to
find any plant under serious attack by the mealybug.
NOT IN JAMAICA - YET
There were reports in
September, 1996, that the mealybug was found in Jamaica. Happily, the experts
have since determined that this was a false alarm. This only goes to show how
difficult it is to distinguish between one mealybug and the next by physical
appearance. Nonetheless, it may be just a matter of time before it is here. So
vigilance must be maintained and preparations continued for possible entry.
So far, Grenada, where
it seemed to have first entered the Caribbean, followed by Trinidad, St. Kitts,
St. Lucia and more recently Guyana have borne the brunt of the attack. Initial
reports from the islands were most disquieting. Multiplying at a rate much
faster than customary in its countries of origin (Australia, Indonesia,
Philippines, India and South East Asia, Middle East and Africa), it was
ravaging agriculture and horticulture and even forestry leaving a trail of
damage valued at over US $150 million in two years.
DON’T LOOK FOR PINK
Also known as the
hibiscus mealybug, and the grape mealybug in various parts of the world, this
sucking insect is perhaps more readily identifiable by the damage it does than
by the colour “pink” that the name suggests. Sure, it is pink if the white waxy
coating is removed from its 3 mm long, oval-shaped adult body. But then there
is already a “pink mealybug” (Saccharicoccus sacchari) in sugar cane.
This is however well controlled by natural enemies, though it may be
occasionally found beneath leaf sheaths, at the cane joints, particularly in
water-starved or partly abandoned fields. Here too, the pink is usually not
visible under the coating of white wax.
It may take many
painstaking hours of peering under a microscope for the trained expert to
distinguish between one type of mealybug and the next. Even the layperson
however will readily recognize that something unusual is afoot when faced with
an attack by this new pest.
DAMAGE
As it feeds, the pink
mealybug (Maconellicoccus hirsutus) injects toxic saliva, in reaction to
which leaves curl and crinkle while stalk growth becomes stunted so that leaves
appear bunched together. These symptoms are sometimes produced even where the
mealybug merely pauses to sample a plant it may subsequently reject.
Where the bug comes
across a plant it truly fancies the results are much more dramatic. Most Hibiscus species,
including the popular ornamentals used to form hedges, the blue mahoe (the
national flower), sorrel (Christmas favourite), as well as okra, will rapidly
become almost totally covered - the tender tip of the stem, especially, and
even exposed roots - by teeming masses of the bugs. With their constant sucking
of the plant sap they pass out a sugary liquid called honeydew which coats the
leaves encouraging growth of the black sooty mould fungus, often referred to as
“blight.”
Despite its famed
preference for plants of the Hibiscus species, it is hard to
say whether it does not savour fruits most of all. Pictures of surfaces of
fruits such as soursop, sweetsop, guava, pumpkin etc. completely covered, with
literally not a centimeter of visible surface, tell the story. Fruits not
directly attacked are so deformed, they become useless. The list of popular
plants attacked given in Table 1 shows our potential vulnerability.
If it enters and is
allowed to go unchecked the mealybug would have the capability of devastating
watersheds and would threaten Jamaica’s mahoe forests and the magnificent
century-old guango trees that dot the countryside. There would indeed be grave
implications for water resources, food supplies, the treasured greenery and
consequently even tourism.
WHY SO DEVASTATING?
Pink mealybug is of
little importance in its countries of origin. Why then is it so damaging in the
Caribbean?
The explanation is
simple. In its homeland it is suppressed by a range of natural enemies - other
insects mainly - that prey upon or parasitize it. Leaving those natural enemies
behind, it arrived in the Caribbean unfettered and free to realize its full
reproductive and damaging potential. Now that it has been rejoined by its
natural enemies its capacity for devastation has been dramatically reduced.
SPREAD
Because females lack
wings, spread would normally be relatively slow. Unfortunately, human beings
are the most efficient agents of dispersal taking plant material, usually
unknowingly infested, from place to place, sometimes from country to country.
In addition the mealybug
can piggyback on clothing, packages of various sorts, and animals - including
birds. It can be wind blown or washed to other sites in streams and may
infested material to the
authorities for identification. You could be spreading the insect along the
way. Call them for an on-site inspection. If you are a cane farmer your best
bet would be to:
Call SIRI at 962 2241/
962 1287 or the nearest RADA office.
When presence of the
mealybug is confirmed, burn cuttings from infested plants as close as possible
to the site. Don’t put them with garbage to be taken to the dump. Also avoid
shaking or scattering infested material.
CONTROL
In instances of an
insect outbreak it is customary to look to insecticides for an immediate
solution. While there will indeed be a place for insecticides, the mealybug is
not easily controlled by chemicals.
The waxy covering
shields it from insecticidal sprays. Furthermore the bugs tend to congregate in
cracks and crevices in the bark of trees, within curled up leaves, beneath the
sepals of flowers and even under rocks on the ground. In such locations many
will escape the best directed spray. In addition when the mealybugs attack
full-grown mahoe or guango trees, only aerial spraying could potentially reach
them.
The frequency with which
such spraying would have to be conducted would not only prove harmful to our
own health but more damaging in the long term as natural enemies would also be
destroyed creating the possibility of even greater outbreaks of the mealybug
and unpredictable secondary outbreaks of other pests.
Don’t start spraying
every mealybug in sight. This could do more harm than good. Infestations of our
native mealybugs may well be sustaining populations of natural enemies that
could be helpful in fighting this expected invader. Spraying will kill these
beneficial insects.
Insecticides may however
be judiciously used in an effort to protect certain crops. Precise
recommendations will depend on type of crop and should follow initial testing.
In the long run, the
solution lies in the importation, rearing and release of natural enemies such
as certain ladybird beetles and parasitic wasps (which pose no danger to humans
or livestock) which will establish themselves to counter the buildup of the
mealybug.
OUTLOOK
The mealybug ought not
to be as devastating in Jamaica as it has been in Grenada. For one thing, we
have had ample time for preparation. The Ministry of Agriculture and press have
done an excellent job in alerting us to the danger. We need to maintain the
vigilance and play our part in observing quarantine regulations and continue to
immediately report sightings of suspected mealybugs.
Entry of the mealybug to
Jamaica would have to be regarded as a national emergency requiring the full
cooperation of all agencies. The goal must be to provide a welcoming party of
so many of the mealybug’s natural enemies that it feels right at home in
Jamaica.
That is why SIRI plans
to join the national effort to rear natural enemies.
Total eradication after
arrival is unlikely. It should however be possible to so integrate it into the
local environment that after a while its presence becomes hardly noticeable.