|
Cocoa
 Mealy bugs (Pseudococcidae)
This cosmopolitan group of insects with
exceptional powers of dispersal is often seen colonizing cocoa in most
of the cocoa growing tracts of
South East Asia
like India, Sri Lanka and Papua New Guinea. Though few species of mealy
bugs colonize cocoa trees, two species of Planococcus and one species of
Planococcoides are the most important and most abundant of cocoa
insects. They are the cocoa mealy bug, P.lilacinus, the citrus mealy
bug, P.citrii and the West African mealy bug, Planococcoides njalensis.
In India, the cocoa mealy bug, Planococcus lilacinus (Ckll.) is reported
as a serious pest causing damage to cocoa and is present in all cocoa
tracts of the country. It occurs consistently on the plant, and is
present throughout the year. This colonizes the tender parts of the
plant such as the growing tips of the shoots, the terminal buds, the
flower cushions, the young cherelles and mature pods.
Mirids (Miridae)
Mirids are one of the most important of cocoa
insects in many of the cocoa cultivating areas of the world. The most
important mirids of cocoa are Sahlbergella singularis Hagl and
Distantiella theobroma (Dist.), which occur in West and
Central Africa.
Of these, S. singularis is the major pest of cocoa in Nigeria. In South
and Central America, mirids of the genus Monalonion are attacking cocoa
for over 100 years. The genus Helopeltis, first recorded as a pest in
Sri Lanka more than a hundred years is also found in Indonesia,
Malaysia, and India. H. theivora Westwood and H. antonii Sign. are
reported from Sri Lanka, Malaysia, Indonesia, India, and Taiwan etc. H.
clavifer, Pseudodoniella laensis Miller, P. typica and P. pacifica occur
in Indonesia, Malaysia and Papua New Guinea.
Other
pod feeding bugs
Shield bug
Cocoa pod feeding shield bug, Bathycoelia
thalassina (H.S.) (Pentatomidae) is a comparatively new pest in
West
Africa and is at present noticed from
Ivory Coast
to Cameroon. The eggs are laid in groups on leaves, trunk and branches.
The feeding is restricted to pods. These bugs with their long stylets
penetrate the husk and the contents of the beans are sucked out so that
they become empty and brown. Only a minute lesion is left on the feeding
surface. But slicing affected pods will reveal the empty beans and the
tracks left through the husk by the stylets of the insects.
Coreid bug
Coreid bugs are important in cocoa - coconut
interplantings since some coreids are pests of coconut also like
Pseudotheraptus. Two genera are associated with cocoa. They are
Theraptus and Pseudotheraptus. Feeding by P.devastans inhibits
development of cherelles and causes distortion of old pods. This is more
prevalent on hybrid and Amazon cocoa probably because pods are more
continuously present throughout the year. Another coreid important in
cocoa is Amblypelta. A.cocophaga attack the stem of cocoa in
Solomon Islands
but in Papua New Guinea A.theobromae feeds mainly on cherelles and young
pods causing distortion and necrosis.
Other
Hemipterans
Many homopterans occur on cocoa but most of them
are of minor importance. The leafhoppers Empoasca devastans in
Sri Lanka,
Affroccidens species in
Ghana,
and Chinaia rubescence in
Costa Rica
cause distortion and premature drop of leaves. In Trinidad, Brazil,
Guyana, Costa Rica and Colombia, a membracid, Horiola picta feeds on
flower cushions, pods and stems and may cause pod wilt. Gargara spp and
Leptocentus sp are reported from south India as feeding on flower buds,
cherelles, pods and tender shoots and they are present throughout the
year as a minor pest. The psyllid, Tyora tessmanni is important in
Africa.
Two species of aphids occur on cocoa. The
abundant and cosmopolitan one is the citrus black aphid, Toxoptera
aurantii B.d.Fos. This aphid colonizes the flower buds, flowers, flush
leaves, tender stems and very small cherelles. Leaf crinkling and
shedding of flowers are the outcome of infestation. A number of natural
enemies feed on the aphids and reduce the population. These include
syrphids, cecidomyiids, coccinellids, hemerobiids etc. In severe cases
of infestation spraying with dimethoate at 160ml in 100 litres of water
is suggested.
Thrips (Thripidae) usually make their presence
felt only when the plants are stressed for water. Out of the few species
of thrips that feed on cocoa, the red-banded thrips, Selenothrips
rubrocinctus (Giard) is the most important and occurs through out the
tropics on cocoa and many other plants. This feeds on the leaves. This
is more important in
West
Indies, Surinam, São Tomé and Ivory Coast.
Leaf
feeding insects
Cocoa trees in all its growing stages exhibit a
pattern of leaf production, known as flushing. During the flush, cocoa
is particularly susceptible to attack by a wide variety of leaf feeding
lepidopteran caterpillars, coleopterans. Seasonality studies of cocoa
insects have shown that the flush associated insects exhibit two annual
peaks, one with each of the major flushes. No significant increase in
numbers of these insects during the minor flushes. Analysis of the
coleopteran from the edge samples revealed a species composition more
like the major flush fauna with characteristically high numbers of leaf
and shoot feeders.
Caterpillars
Caterpillars of few lepidopterans infest the
cocoa trees. Most of the time the cocoa plants can sustain the levels of
defoliation effected by these caterpillars. Since cocoa trees have many
flushing seasons, the incidence of /feeding by these caterpillars have
little effect on the plants. But defoliation can occur in case of
feeding by one or two species of bagworms. The feeding by these can
result in total defoliation and weakening of the trees.
Bollworm Earias bipalga is one of the bollworms
of cotton but its caterpillars constituted the most serious insect
problem in establishing cocoa in
West Africa.
Besides feeding on young trees, the larvae feed on the pericarp of
unripe pods also. This is a pest of cocoa up to three years old and
attack is heavy on unshaded or poorly shaded plants. Destruction of
apical buds delays or even prevents jorquette formation. Vertical growth
of the trees is also affected as seen in Nigeria. It is reported that
cocoa types in which canopy formation proceeds throughout the year seem
least susceptible whereas types with canopy formation is punctuated by
periods of inactivity are most susceptible.
Cocoa armyworm, Tiracola plagiata is wide
ranging species, but it attacks cocoa in
Papua New
Guinea. Initially occasional local infestations were known until
epidemic populations developed in some locations. This happened in areas
where virgin forest had been clear felled and burnt over. The shade
trees like Leucaena leucocephala and Crotalatia anagyroides are also
susceptible to this insect. The insect feeds selectively on apical buds
that lead to large-scale destruction of apical dominance. The severely
attacked trees may show upward spindly growth. Bud destruction in
unshaded young plants with resultant delayed formation of the jorquette
is the most notable consequence of attack by cocoa armyworm moth.
Cocoa lymantriids, are the most commonly
encountered leaf feeding insects of cocoa in
India. The
caterpillars of this moth feed on the tender leaves and on the pericarp
of cherelles and unripe pods. Three genera of lymantriids, viz.,
Lymantria, Euproctis and Dasychira are so far reported on cocoa. The
caterpillars of these moths feed on the tender leaves, and on the
surface tissues of cherelles and green pods. If the damage is very
severe, spraying could be given by mixing 16ml dimethoate in 10 litres
of water.
L. ampla
Walker is
commonly and abundantly observed leaf-feeding insect of cocoa in India.
These are seen more in the field after the monsoon rains. The
caterpillars cause severe damage on leaves in young plants. The early
instars of this moth feed on leaves or the surface tissues of growing
pods during day and night, but later instar caterpillars are nocturnal
in habit. During daytime they hide on fallen leaves at the base of the
tree or the basal surface of the main stem. The indigenous natural
enemies of this lymantriid include the insect pathogen of the mature
larvae, Paecilomyces fumosoroseus; a pupal parasite, and a braconid
larval parasite Apanteles sp.
Caterpillars of Euproctis spp are also
defoliators of cocoa. These caterpillars feed on tender leaves, surface
of cherelles and green pods. The sporadic high population of Euproctis
spp can cause severe damage of tender leaves. The period of attack is
seen from June – July.
Beetles and weevils
Grubs of many scarabaeid beetles feed on roots
and decaying organic matter in the soil. The adult beetles feed on soft
leaf tissues and flowers of cocoa. Leaf eating beetles mainly Myllocerus
sp. and Popillia sp. feed on tender leaves causing a series of irregular
holes. They make sporadic appearance in some areas after rains and cause
serious damage. Grubs of these beetles dwell in the soil. Drenching the
soil with a suspension of carbaryl (Sevin 50%WP) at the rate of 20g in
10 litres of water is effective in controlling the pest.
Ash weevils, viridanus Fab. and M.maculosus Desb.
(Curculionidae) are recorded in the Nilgiris and Yercadu regions as
early as 1967. M.viridanus occur as a major insect in all cocoa growing
tracts of Kerala and Tamil Nadu. Adults are seen in large numbers on the
underside of leaves and feed on the interveinal tissues leaving the
veins intact. The flaccid tender flushes are not preferred for feeding.
Population peak is observed in July- September. Infestation is
relatively severe on young plants and quite often, the entire foliage of
such plants are skeletonised leading to growth retardation. The
incidence of ash weevils is more serious in coconut-cocoa plantations.
Stem boring caterpillars and beetles
Like the leaf feeding beetles and weevils, stem
boring moths and beetle are also more in forest cleared plantations or
plantations near forests in the cocoa growing regions. Borers of both
coleopterans and lepidopterans attack cocoa especially the seedlings and
trees planted near forest plantations. The red borer of coffee, Zeuzera
coffeae Nietn (Cossidae) is a pest in many countries. Caterpillars of
this leopard moth bore into young branches and make unramified hollow
tunnels inside the stem. The symptoms of attack are a round hole on the
stem, drying up of the upper portions of above the hole, and excreta and
chewed up fibres strewn out on the ground. If the main stems of young
plants are attacked, the plants die. When the branches are attacked,
only the branches dry up and simple pruning will save the trees.
The genus Glenea is widespread in the
Old World
tropics, and is reported from
Java,
Papua New
Guinea, New Britain, Malaysia, and India. Several species of this favour
dead and dying trees. Attack seems more common in neglected, overgrown
plantations. Glenea sp is reported from South India as attacking
neglected gardens. Attack is seen mostly in lower trunks and the
branches are rarely attacked. The grubs tunnel into the trunk and
penetrate deeper, making galleries within. The tissues of the bark and
wood are eaten. More than one grub is noticed in a stem. Adults are
found inside dried up wood. Girdling of stem and branches is noticed
sometimes. On younger trees, the pest attack occurs at the jorquette
which normally results in the drying or breaking of the portion above.
Mechanical extraction of the larve and topical treatment with carbaryl
paste are suggested as control measures.
Vertebrate Pests
The vertebrate pests such as rats, squirrels,
palm civets and birds inflict direct loss of the crop by feeding on and
damaging the pods. The rats and squirrels are considered the key
non-insect pests of cocoa in all tropical countries.
Rodents are the major problem in cocoa
interplanted with coconut in all the countries since they have the
ability to exploit new food sources. Rats and squirrels are the main
groups of rodents that damage cocoa in all the cocoa cultivating tracts
of the world. These damage the pods and the attack follows a fairly
constant pattern. Ripe pods are usually chosen and a large hole is
bitten through the pod husk. The beans are the extracted and after the
sweet mucilage is eaten, these are discarded. Squirrels usually make
oval holes on the central or terminal portion of the pods while rats
make oval or round holes near the stalk end of the pods for feeding.
Squirrels are diurnal and rats are nocturnal in habits. Squirrels damage
ripe pods but the rats damage both ripe and immature pods.
Many species of rats damage both young and
mature pods. Rat damage is reported from most of the tropical countries
including the islands. The most important rat species observed is the
black rat Rattus rattus Linn. which is very serious pest of coconuts in
all coconut growing areas. The black rat is recorded in
India as a
major pest occurring in areca –cocoa and coconut-cocoa mixed gardens.
Black rats damage cocoa grown as monoculture also since in any South
Indian condition the vicinity of preferred nesting hosts like coconut is
assured.
Two species of squirrels are reported as pests
of cocoa in
India.
They are the Western Ghats squirrel, Funambulus tristriatus Waterhouse;
the South Indian palm squirrel, F.palmarum. Of these the
Western Ghats squirrel is the most serious pest of cocoa in
India.
Only the cooperative efforts of plantation
owners/small farm holdings can achieve management of rodent population.
Otherwise the local trials done by individual farm owners have no impact
on the population levels of rodents and the damage they inflict on cocoa
and other crops. This is more pronounced in the case of rats. Baiting
and trapping methods are available. The rats can be controlled by
keeping 10g bromadiolone (0.005%) wax cakes on the branches of cocoa
trees twice at an interval of 10-12 days. Squirrels are best controlled
by trapping with wooden or wire mesh single catch live trap with ripe
coconu kernel as the bait. The success is more if trapping is carried
out during the lean periods of the crop (September-November) and when
the alternate foods such as paddy, cashew apples and jack fruit are not
available. The traps are to be inspected daily and the trapped anmals
are to be killed to minimize the chances of commnication with other
animals. Timely harvest of the pods will help in increasing the
efficiency of poison baiting as well as trapping.
The palm civet, Paradoxurus hermaphroditus
Pallas (Viverridae) also known as toddy cat, is a nocturnal tree
climber. It is present in many cocoa-growing tracts of
India,
Malaysia. This carnivore damages the pods by biting and breaking the
husk of cocoa pods. The damage caused by this to cocoa is reported from
south India. The palm civet bite and break the husk of cocoa pods. The
pieces of broken chunks are 2.0 to 3.0 cm in diameter. There is no
distinct pattern for the damage. The terminal half or one side of the
pod is broken. While feeding the beans are swallowed and as such no
trace of beans is visible directly under the tree. Piles of defaecated
beans are seen scattered around the cocoa plantations. Palm civets could
be easily controlled by poison baiting with 0.5g of carbofuran granules
using ripe bananas as baits. Two such banana fruits have to be tied to
the trunk /jorquettes of five to six cocoa trees per hectare. |
