Learn about the pests of coconut and its contol.
1. Coconut Scale, Aspidiotus Destructor Signoret (Hemiptera: Diaspididae):
The coconut scale is one of the most dangerous pests of coconut palm in most of the coconut growing regions. It occurs from Iran to Japan, and USA, and southwards down to South Africa and Australia. In addition, this pest also feeds on other palms, bananas, avocado, cocoa, citrus, ginger, guava, Artocarpus, Pandanus, papaya, rubber, sugarcane, yam and many wild plants. The scale of the female is circular, flat, transparent, whitish to grey white and about 1.8 mm in diameter. The scale of the male is oval and much smaller than that of the female.
Life-Cycle:
The female deposits about 20-25 yellow, tiny eggs under her scale. Incubation takes 7-8 days. On hatching, the crawler takes up a position on the leaf and starts feeding. The male nymph moults three times and the female twice. The larval development takes 24 days. The total life-cycle is completed in 31-35 days and there are about 8-10 generations per year.
The coccinellid predators including Chilocorus sp., Azya trinitalis Mshl., Cryptognatha nodiceps Mshl., Rhyzobius lophanthae (Blaisdell) and Pentilia castanea Muls. (Coccinellidae) play a significant role as natural limiting factor for the coconut scale. The nymphal parasites belonging to genera Comperiella (Encyrtidae) and Encarsia sp. (Aphelinidae) have a more local significance.
Damage:
The scale affected leaves first show a yellow discoloration around areas of the sucking activity, followed by brown necroses. In extreme cases, the leaves dry up, entire fronds drop off, the crown dies and the whole crop is lost.
Control:
Spray 500 ml of malathion 50EC in 250 litres of water per ha.
2. Black-Headed Caterpillar, Opisina Arenosella Walker (Lepidoptera: Xyioryctidae):
Next to the rhinoceros beetle, this caterpillar is the most important pest of coconut palm in Kerala as well as along the western coast of India, Sri Lanka and Myanmar. The moth is ash grey. It is medium-sized, measuring 10-15 mm, with a wing expanse of 20-25 mm. The caterpillars feed hidden inside silk galleries on the underside of leaves.
Life-Cycle:
A female moth lays 125 scale like eggs in small batches on the underside of the tips of the old leaves. Freshly laid eggs are creamy white and turn pink on completion of embryonic development. The incubation period lasts about 3-5 days in summer and 10 days in winter. A young larva is about 1.5 mm in length and increases to 15 mm before pupation.
It feeds on green matter and simultaneously constructs a silken gallery in which it feeds and voids frass. When full-grown in about 40 days, the larva transforms itself into a brownish pupa inside the gallery. Within about 12 days, a whitish moth emerges and starts the life-cycle all over again.
The caterpillar is parasitized by Apanteles taragammae Vier, Bracon brevicornis Wesmael (Braconidae) and Elasmus nephantids Gahan (Elasmidae). Inundative releases of native parasitoids, Goniozus nephantidis (Muesebeck) and B. brevicornis at 3000 and 4500 ha-1, respectively have given encouraging results for management of black-headed caterpillar.
The pupa is parasitized by Tricliospilus pupivora Ferrieri (Eulophidae), Stomatoceras sulecatiscutellum Gir and Brachymeria nephantidis Gahan (Chalcididae) and Xanthopimpla punctata Fabricius (Ichneumonidae). A bacterium, viz. Serratia marcescens Bizio (Entero-bacteriaceae) has also been reported from this pest.
Damage:
As a result of the numerous galleries made by the feeding caterpillars, the foliage dries up. Infested trees can be recognized from the dried up patches in the fronds. In certain years, the population of the pest is quite high and damage to foliage becomes very prominent, resulting in a considerable reduction in yield.
Control:
(i) Cut and destroy the first infested fonds by burning.
(ii) Apply 2.5 litres of chlorphyriphos 20EC in 625 litres of water per ha.
3. Rhinoceros Beetle, Oryctes Rhinoceros (Linnaeus) (Coleoptera: Scarabaeidae):
The rhinoceros beetle is one of the most important pests of the coconut and other palms. It is found throughout South-east Asia, the Philippines and southern China. It was introduced
into the South Pacific Islands during the first decade of this century and reached Mauritius in the sixties.
The stoutly built beetle has a pointed horn on its head, is elongate and cylindrical and measures about 4-5 cm. It has well-developed wings and can fly long distances. It is harmful only in the adult stage when it feeds on the crown of the coconut tree. The larvae, however, feed on decaying organic matter in the ground.
Life-Cycle:
The oval, white, seed-like eggs are laid 5-15 cm below the soil surface in decaying organic matter. The early stages of the beetle are, therefore, not found on trees, but are generally passed in manure pits and decomposing vegetable matter, chiefly in the dead palm trunks.
A female may lay 100-150 eggs which hatch in 8-18 days and the grubs start feeding on the decaying matter found in the vicinity. The larvae pass through three instars to complete their development in 99-182 days (mean 130 days). The optimum temperature for development of the larvae is 32-40°C. Pupation takes place in chamber at a depth of about 30 cm and the beetles emerge after 10-25 days.
They remain in the pupal cell for about 11-20 days before coming out of the soil and, on emergence; they are soft-bodied creatures. Soon, they fly to the nearest palm-tree and start the attack. They lay eggs after 20- 60 days. The beetles are active at night and may be attracted to a source of light. The adults can live for more than 200 days. Generally, one generation is completed in a year.
The natural enemies of the grubs are Sarcophaga fuscicauda Botlcher (Sarcophagidae) and Pheropsophus hilaris var. sobrinus Daj (Carabidae). The exotic predatory bug, Platymeris laevicollis (Distant) has shown considerable promise against this pest. The frogs, toads, birds, rats and squirrels also prey upon grubs of this pest. The grubs are also infected by Metarrhizium anisopliae (Metchnikoff) and Beauveria bassiana (Balsamo) Vuillemin (Monillaceae).
Damage:
The beetles throw out a fibrous mass while feeding in the burrows made in the young fronds. The injury is seen as a series of holes on the fronds when they open out. As a result, the growing point is soon cut off and the tree dies. The damage caused by this beetle is more serious on young trees. Besides the coconut and date-palm, the beetle also attacks palmyra and some other plants.
Control:
(i) Maintenance of sanitation in coconut gardens by proper disposal of decaying organic debris is an important step.
(ii) Hook out the beetles from the affected crown by means of hooks during July-August (A hooked metal rod about 0.6 metre long and 0.8 mm thick with a hook at one end and a handle at the other end will serve the purpose).
(iii)Treat the breeding places with 2.0 kg of carbaryl 50WP in 250 litres of water per ha.
(iv) Drench the manure heaps upto a depth of 60 cm at quarterly intervals.
(v) Baculovirus inoculated beetles @ 10-15 per ha can be released to bring down the pest population.
4. Red Palm Weevil, Rhynchophorus Ferrugineus (Olivier) (Coleoptera: Curculionidae):
The pest is distributed in India, Pakistan, Bangladesh, Sri Lanka, Malaysia, the Philippines and New Guinea. It is one of the most destructive pests of coconut palm in Maharashtra, Assam, Kerala, Tamil Nadu, Mysore and Orissa. It is also found on date palm.
This weevil is reddish-brown, cylindrical, with a long curved snout. The male has tuft of hairs along the dorsal surface of the snout, whereas the female is without it. The weevil is incapable of causing direct damage but in the early stage, it is harmful.
Life-Cycle:
The mother weevil scoops out a small hole with its snout in the soft tissues of the trees or in the existing wounds, in the crown or trunk and lays an oval, whitish egg. A weevil may lay up to 200-500 eggs in its life-span of 3-4 months. The eggs hatch in 2-5 days and the soft whitish grubs on hatching feed on the soft tissues and tunnel into the tree trunk. When full-fed, the grubs measure about 65 mm and are yellowish.
The larval period ranges from 2 to 4 months. The grub changes into a pupa after spinning a cocoon. The weevil emerges from this cocoon on the completion of the pupal stage in about 14 days. The adults remain within the case for 11-18 days out of life-span of 50-113 days, the male surviving for a longer period than the female. The adult is capable of flight and is diurnal in habits.
Damage:
The larvae feed on the soft tissue of trees and often cause very severe damage, especially when a large number of them bore into the soft growing parts. The borer attacks all palms, including the coconut, the date-palm and the sago- palm (Metroxylon spp.). The weevil is attracted to the trees by the smell of palm juice, which flows as a result of the wounds caused by man or other agents. The dead palms also attract these insects. The pest multiplies quickly in young coconut plantations.
Control:
(i) Destroy the infected, dying and dead palms.
(ii) Cut petioles 120 cm away from the trunks to prevent entry of weevil.
(iii) Inject emulsion of dimethoate 30EC @40 ml or chlorptriphos 20EC @ 2.0 litres or carbaryl 50WP @ 250 g in 25 litres of water into the live holes and plaster them with mud after application of chemicals.
(iv) Apply 2.0 litres of chlorpyriphos 20EC in 250 litres of water to the damaged trunks or spray on crowns after every three months.
5. Coconut Weevil, Diocalandra Frumenti (Fabricius) (Coleoptera: Curculionidae):
The grubs of this weevil attack coconut palm, date- palm, the oil and nipa-palms and sorghum. The pest is recorded from Sri Lanka, Myanmar, South India, Malaysia, Thailand, Indonesia and the Philippines.
The adults are small weevils (6-8 mm in length) shiny blackish with four large reddish spots in the elytra.
Life-Cycle:
Eggs are laid in crevices at the base of the adventitious roots at the foot of the trunk, flowers, and petiole or at the base of the peduncle. The eggs hatch in 4-9 days. Larval development takes 8-10 weeks and the pupal period lasts 10-12 days. The life-cycle is completed in 10-12 weeks.
Damage:
The grubs attack all parts of the coconut palm particularly the roots, the leaves, and the fruit stalks. As a result of this attack there is premature fruit-fall. The loss of yield is appreciable.
Control:
Spray 2.0 kg of carbaryl 50WP in 500 litres of water per ha.
6. Coconut White Grub, Leucopholis Coneophora Burmeister (Coleoptera: Melolonthidae):
It is a major pest of coconut, tapicoa, yam, colocasia, sweet potato and banana in South India, particularly in Kerala. The beetles are chestnut coloured and measure 16 mm in length. They defoliate the plants and the whitish grubs feed in the soil on roots of host plants.
Life-Cycle:
Immediately after the first showers of southwest monsoon during June, the beetles come out of the soil, fly about for some time and mate. Then they lay eggs in the soil near the palms during June-July. The eggs are laid at a depth of 7-15 cm. The eggs hatch in 20 days and the grubs start feeding on roots.
They moult a number of times and when full-grown they pupate, within a period of ten months or so. The pre-pupal period is 9- 12 days and the pupal stage lasts 25 days. The insect completes one generation in a year. Birds, squirrels, dogs, cats and bats are the natural enemies.
Damage:
The beetles defoliate the host plants. As a result of continued feeding of the grubs on roots, the vitality of the palms is reduced and their colour becomes yellowish. In the end trees become very weak and show the symptom of premature falling of the nuts.
Control:
Dust the soil with chlorpyriphos 2 per cent @ 30 kg per ha.
7. Coconut Eriophyid Mite, Aceria Guerreronis Keifer (Acarina: Eriophyidae):
This mite has been reported as a serious pest of coconut in Kerala and Tamil Nadu.
Life-Cycle:
A female lays about 18 eggs and the mite completes a generation in 9-12 days.
Damage:
The mites are seen in colonies in the perianth of developing nuts and live in the white tender portion covered by the inner bract of perianth and suck the sap from the tender meristematic mesocarp tissues. Maturing nuts up to nine month old harbour the mites. The feeding results in warts and numerous longitudinal fissures on the husk of developing nuts.
Control:
(i) Root feed with 10 ml of monocrotophos 36WSC in 10 ml water per palm.
(ii) A combination treatment involving 500 ml of 0-03 per cent azadirachtin oil formulation and 100g talc based product containing the fungus, Hirsutellci thompsonii (having spore count of 1 × 107) in 200 litres of water, has been found promising.