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COCONUT SCALE Aspidiotus destructor Signoret -- Homoptera, Diaspididae (Contacts) ----- CLICK on Photo to enlarge &
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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). Following 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. |
