Levuana irridescens Bethune-Baker -- Lepidoptera, Zygaenidae
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This small purple moth became a serious pest in Fiji in 1924, where the entire copra industry was threatened with disaster and the Government of Fiji ordered a prize of 5,000 pounds to anyone who could devise a solution to the problem (DeBach 1974). However, the offer was withdrawn when it was considered that the only practical solution to the problem was a biological one, requiring trained entomologists. Working cooperatively with H. W. Simmonds, the Government Entomologist, Dr. J. D. Tothill, R. W. Paine and T. H. C. Taylor were hired to initiate the biological control attack.
Coconuts were the chief income of the native Fijians and enabled islands to be inhabited and prosper that otherwise would be uninhabited. Historically the coconut moth was restricted to the large island of Viti Levu where it was considered native. Because of the damage, coconuts were never considered a commercial crop there. The threat developed as the moth spread to other islands causing defoliation and crop failure. The coconuts on islands attacked by L. irridescens turned from the normal fringe of shining green fronds to a band of lifeless grey. At the close of an outbreak not a single green palm was to be found.
Because the coconut moth was originally known only from Viti Levu and there it had no parasitoids of consequence, it was suspected that it might be exotic. However, careful searches throughout the south Pacific islands and southeast Asia, coconut moth was never found outside of Fiji. However, a related moth, Artona catoxantha, had been known for some time to occur in Java and Malaya and to be heavily parasitized. In 1924 attempts were made through cooperating entomologists to obtain parasitoids from A. catoxantha. Several species were collected in abundance in Java and twice sent by ships' cold storage to Fiji, but as the voyage was prolonged by routes through Australia (4,000 miles), and took one month, the parasitoids failed to survive.
At the time biological control was still in its infancy and no single approach was considered. It was, for example, decided to import a series of generalist parasitoids of non related hosts from Hawaii in the hope that they might attack coconut moth. There were attempts to increase predation with an ant, Oecophylla smaragdina, which was used in the Orient to control pests on citrus. Even insectivorous birds were considered for importation from Sri Lanka and India, etc. These approaches either failed or were finally rejected as impractical, undesirable or unfeasible. The parasitoids of A. catoxantha were again considered for introduction, even though success was thought to be improbable due to the necessity of transferring from Artona to Levuana. Often host specificity prevents such transfers; but, as was learned from studies of moths in Canadian forests, in certain cases the same parasitoids could attack distinctly different host species.
Drs. Taylor, Tothill and Paine conducted additional explorations in Melanesia and Indonesia in 1925, and nine species related to Levuana were found, most of them being quire rare and heavily parasitized. When Taylor returned to Fiji with a shipment of parasitoids, all had died. Because of the rarity of most species, and the fact that Artona catoxantha was more readily available in Java and other parts of Indonesia and was known to have at least two active parasitoids, Ptychomyia and Apanteles, it was decided to concentrate on their importation. While H. W. Simmonds was in Kuala Lumpur early in 1925 to seek out a Artona outbreak, Taylor was travelling in Malaysia when he located a small outbreak of Artona about 300 miles from Singapore at Batu Gajah. Both species of parasitoids were present. Simmonds joined him there to prepare as large a shipment as possible for Fiji, which was gathered into 17 large Wardian-type ventilated cages, each of which would hold 4-5 small coconut seedlings infested with both parasitized and unparasitized Artona larvae. The latter were to serve as hosts for egg-laying parasitoids that emerged en route. About 20,000 larvae were placed on the 85 young palms and sent 300 miles to Singapore by rail.
There were great difficulties encountered in getting shipments through alive. It had been decided that direct shipment from Singapore to Fiji was required in order to avoid Australian quarantines. However, there were virtually no direct sailings so that most shipments went by Australia anyway. Also the collections and shipments had to be made when the insects were available, but this had to coincide with the avai8lability of a ship which often was months apart. About the only hope was the Clan Line of cargo boats which sailed between London and Fiji, sometimes via Singapore. In June it was learned by cable that the Clan Mackay would sail from Singapore on July 10 for Fiji but not directly. Meanwhile it was learned, again by cable, that Clan Matheson was sailing from Java directly to Suva, Fiji, on July 10, so for an extra 250 pounds sterling the Clan Mackay was instructed to call at Surabaya, Java, to transfer the parasitoids to the Clan Matheson which would be ready to sail (DeBach 1974). This saved several days although it still took 25 days following collection to reach Suva. Taylor accompanied this shipment to supervise and care for it en route, arriving in Suva on Aug 3, 1925, when he immediately conveyed the cages to a quarantine insectary. About 315 live adult parasitic flies of Ptychomyia but no Apanteles survived. The tachinid flies were transferred to cages stocked with Levuana larvae and immediately attacked them. By August 21 the first generation of new adult flies began to emerge and insectary culture was assured. Within six months over 15,000 flies had been bred and colonized over the coconut moth infested area. The potential of the fly was first realized when just two months after the importation, parasitoids were found to be accidentally established around the insectary. From this time in October onward, the dispersal of the fly was very rapid and it was found to be established throughout all host infested zones within six months of the first liberation.
Within three months of liberation of the Suva colony, Levuana was exterminated on the original release trees. Six months after the initial introduction of Ptychomyia, many of the outbreaks had subsided completely. When the final report was written in 1929, there had been no new outbreak of Levuana for three years. DeBach (1974) noted that it seemed especially significant that this single natural enemy, P. remota, apparently gave better control of its adopted host L. irridescens than it did of its native host Artona (Tothill et al. 1930) (also see Gater 1925, 1926a,b, 1928; Simmonds 1930, van der Vecht 1950, O'Connor 1953, and Clausen 1978).
REFERENCES: [Additional references may be found at: MELVYL Library ]
Clausen, C. P. 1978. Zygaenidae. In: C. P. Clausen (ed.), Introduced Parasites and Predators of Arthropod Pests and Weeds. U. S. Dept. Agric., Agric. Handbk. No. 480. 545 p.
DeBach, P. 1974. Biological Control by Natural Enemies. Cambridge University Press, London, New York. 323 p.
Gater, B. A. R. 1925. Some observations on the Malaysian coconut zygaenid (Artona catoxantha Hamps.). Malayan Agric. J. 13: 92-115.
Gater, B. A. R. 1926a. Further observations aon the Malaysian coconut zygaenid (Artona catoxantha Hamps.) and its parasites. Malayan Agric. J. 14: 304-50.
Gater, B. A. R. 1926b. Further observations on the Malaysian coconut zygaenid (Artona catoxantha Hamps.) and its parasites. Malayan Agric. J. 14: 304-50.
Gater, B. A. R. 1928. The Malayan coconut zygaenid (Artona catoxantha Hamps.) and its relation to Levuana iridfescens B. baker, in Fiji. 3d Pan-Pacific Sci. Cong. Proc. 2: 2082-85.
O'Connor, B. A. 1953. Biological control of insects and plants in Fiji. 7th Pacific Sci. Cong. Proc. (1949) 4: 278-93.
Simmonds, H. W. 1930. Problems in biological control. The gap in the sequence of generations in Artona catoxantha, the coconut leaf moth of Malaya. Trop Agric. (Trinidad) 7: 215-19.
Tothill, J. D., T. H. C. Taylor & R. W. Paine. 1930. The coconut moth in Fiji. A history of its control by means of parasites. Publ. Imp. Bur. Ent., London. 296 p.
van der Vecht, J. 1950. The coconut leaf moth (Artona catoxantha Hamps.). Pt. I. Life history and habits of Artona catoxantha, its parasites and hyperparasites. Min. Agric. Gen. Agric. Res. Sta., Bogor, Contrib. 110: 1-77.