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COCONUT SCALE, Aspidiotus destructor Signoret -- Diaspididae

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The coconut scale posed a serious problem to the copra industry in Fiji just about the time that the coconut moth, Levuana irridescens B.-B.-, was coming under successful biological control. Coconut scale was first recorded as a pest of bananas in 1912 and in 1916 of coconuts. Damage was severe enough to cause H. W. Simmonds, the Government Entomologist in Fiji, to seek natural enemies in Tahiti in 1920 where the scale was known to be present in lower numbers. Two parasitic species imported and established were Aphytis chrysomphali Mercet and Aspidiotiphagus citrinus Craw, and by 1925 these were distributed to many islands in the Fiji group. The parasitoids spread rapidly and were considered to be doing some good, but the scale continued to spread to new islands, causing severe outbreaks (DeBach 1974).

Coconut scale prefers the underside of leaves where it sucks plant juices. Severe infestations forms a continuous overlapping crust of thousands of scales per leaf, resulting in the leaf turning yellow, withering and sometimes dying. By 1927 in spite of rigid quarantines, coconut scale had spread to nearly all of the Fiji islands and was the most serious pest of coconut in Fiji since coconut moth. In 1926 an attempt was made to secure additional natural enemies from Java. Dr. T. H. C. Taylor was given the assignment, which was plagued with transportation difficulties because of the lengthy sea voyage and the paucity of ships sailing from Java to Fiji. However, Taylor was able to make arrangements to ship his parasitoids and predators on a vessel carrying a cargo of other organisms to Fiji: laborers from India. The steamer Ganges out of India, stopped in Java on January 1, 1927 and sailed on to Fiji on January 2 with Taylor and his infested coconut palms in Wardian cages. Three weeks later they arrived in Fiji, but a severe outbreak of smallpox on board prevented the shipment from being landed at Suva, but rather on the quarantine island of Nukulau, where the insects had to be tended for another five weeks with poor rearing facilities and limited stocks of scales. Therefore, although some parasitoids and predators were colonized on Nukulau and later around Suva and some recoveries made, no permanent establishment occurred (DeBach 1974).

After mid 1927, it was evident that the natural enemies from Java either were ineffective or were not established. Therefore, J. D. Tothill, then Director of Agriculture for Fiji, assigned Taylor to go to Trinidad to investigate several species of laydbird beetles which Urich had recorded as being important factors in the control of coconut scale there (DeBach 1974). Taylor began his work in Trinidad in September 1927 with a survey of the natural enemies present. He found five species of ladybird beetles to be somewhat common and effective, even though at times they were heavily attacked by parasitoids. These latter he subsequently took care to exclude from the shipments that he made to Fiji. By January 28, 1928, his collections of ladybird beetles and stocks of scale-infested palms were ready and were loaded on board ship. Nine large cages were used, holding 6-8 or more infested young palms. Three newly designed extra large cages required four men to lift and more them. Additional food for the predators in the form of 80 heavily scale-infested young palms were carried along in 5-gal. tins. All had to be carefully arranged to protect them from rough handling and damage from salt water during the voyage.

Although the initial predator stocks were limited to 200 adult beetles, plus some larvae and pupae per cage, the predators increased so rapidly during the voyage that many had to be removed to keep them from completely eliminating the food supply and thus starving to death before arrival in Fiji. Trans shipment of the stock was made at Panama on February 1, 1928 to a steamer going via Tahiti to Suva, Fiji, the entire trip taking a little more than five weeks. All five species of ladybird beetles arrived in Fiji in sufficient numbers to enable culture, but more than twice as many Cryptognatha nodiceps Mshl (1,517) as compared to all of the other four species (746) cultured, which may have been an indication of the ultimate dominant role played by C. noticeps.

Insectary culture in Fiji was difficult, so a method was devised of breeding in the field within cloth sleeve covered, heavily infested banana leaves. In each sleeve, starting with 20 beetles, about 300 would be recovered in one month's time, a return of 15:1 with minimum expense and labor. By September 1928 only C. nodiceps was cultured small numbers remaining of the other four species were liberated. Some of the latter became temporarily established but eventually disappeared.

The coconut scale problem was reduced to non economic levels on all important islands in Fiji within nine months. After 18 months the scale was so rare if was difficult to find. During the peak of the reductions, adult beetles and larvae swarmed on every tree and the adults could be readily seen flying around in the air. The trees changed from yellow to bright green. When Taylor published his report of this success in 1935, not a single new outbreak had occurred. The same results occurred on all host plants, many of which had been as badly infested as coconuts (Taylor 1935). DeBach (1974) reported that he visited Fiji in 1969 and found hardly any coconut scale, even though an occasional Cryptognatha adult was seen rapidly searching the clean leaves. He stated it is evidently an excellent searcher that can survive at very low host densities like the vedalia beetle. Additionally it probably feeds on alternative host scales on other host plants. DeBach (1974) found the Aphytis mentioned earlier as being rather common on coconut scale in Fiji. Out of only one light infestation of the scale on avocado, parasitization by Aphytis was considerable, and he thought that some credit also might be given to the parasitoid (DeBach 1974).

In Mauritius Chilocorus politus and C. nigritus eliminated the threat of coconut scale to plantations. Spectacular control of coconut scale was achieved in New Hebrides as a result of Rhizobius pulchellus Montrozier (Cochereau 1965). See Rosen & DeBach (1978) for biological control activities against coconut scale in other countries.

A subspecies of coconut scale, Aspidiotus destructor rigidus Reyne, was discovered in Indonesia. Its life cycle is about 1 1/2 times that of the typical coconut scale, and the female lays only 10-12 eggs. It has somewhat different host preferences than the typical form, but may cause severe damage to coconut (Reyne 1947). Comperiella unifasciata was introduced but never attained high parasitization (Reyne 1948). In South Bali, Aspidiotiphagus citrinus reportedly controlled coconut scale completely by 1936 (Voute 1937) (also see Reyne 1948, Simmonds 1960, Wilson 1960 and Wolcott 1960).

REFERENCES: [Additional references may be found at: MELVYL Library ]

Balachowsky, A. 1948. Les cochenilles de france, d'europe, du nord de l'afrique et du bassin mediterraneen. IV. Monographie des Coccoidea. Classification--Diaspidinae (Premiere Partie). Hermann et Cie., Paris. 154 p.

Cochereau, P. 1965. Contre un ravageur du cocotier aux nouvelles-Hebrides. Controle biologique d'Aspidiotus destructor Signoret (Homoptera-Diaspinae) par Lindorus lophantae Blaisd. (Coleoptera-Coccinellidae) Ile Vate. Oleagineaux 20: 507-12.

DeBach, P. 1974. Biological Control by Natural Enemies. Cambridge University Press, London & New York. 323 p.

Ferris, G. F. 1938. Atlas of the scale insects of North America, series II. Family Diaspididae. Stanford Univ. Press, Stanford, California.

Moutia, L. A. 1942. Division of Entomology. Mauritius Dept. Agr. Rept. 1941: 14-21.

Moutia, L. A. & R. Mamet. 1946. Review of twenty-five years of economic entomology in the Island of Mauritius. Bull. Ent. Res. 36: 439-72.

Reyne, A. 1947. Notes on the biology of Comperiella unifasciata Ishii and its host Aspidiotus destructor rigidus nov. subspec. Tijdschr. Ent. 88 (1945): 294-302.

Reyne, A. 1948. Studies on a serious outbreak of Aspidiotus destructor rigidus in the coconut palms of Sangi (North Celebes). Tijdschr. Ent. 89 (1946): 83-123.

Rosen, D. & P. DeBach. 1978. Diaspididae. In: C. P. Clausen (ed.), Introduced Parasites and Predators of Arthropod Pests and Weeds. U. S. Dept. Agric., Agric. Handbk. No. 480. 545 p.

Simmonds, F. J. 1960. Biological control of the coconut scale, Aspidiotus destructor Sign., in Principe, Portuguese West Africa. Bull. Ent. Res. 51: 223-37.

Taylor, T. H. C. 1935. The campaign against Aspidiotus destructor Sign. in Fiji. Bull. Ent. Res. 26: 1-102.

Voute, A. D. 1937. The biological control of insects in the Netherlands East Indies. Natuurk. Tijdschr. V. Nederland.-Indie 97: 28-34.

Wilson, F. 1960. A review of the biological control of insects and weeds in Australia and Australian New Guinea. Commonwealth Inst. Biol. Control. Tech. Commun. 1: 102 p.

Wolcott, G. N. 1960. Efficiency of ladybeetles (Coccinellidae: Coleoptera) in insect control. Puerto Rico Univ. J. Agric. 44: 166-72.