Historical Review of Control Programs for Levuana iridescens (Lepidoptera: Zygaenidae) in Fiji and Examination of Possible Extinction of This Moth by Bessa remota (Diptera: Tachinidae)

Coconut production in Fiji was a mainstay of the economy and indigenous culture in the late 1800s to early 1900s. From around 1877 coconut production on Viti Levu was severely affected by Levuana iridescens BetheuneBaker, a small purple moth, whose larvae trenched the underside of coconut leaves. A variety of cultural and chemical control strategies over approximately a 16-yr period failed to bring this pest under effective control. A biological control program initiated in 1925 resulted in importation and release of a parasitic fly, Bessa remota (Aldrich), which provided immediate and effective control of L. iridescens. This well-documented classical biological control program has subsequently become highly controversial with regard to arguments over endemicism of L. iridescens to the Fijian archipelago and the possibility that B. remota has caused the extirpation of L. iridescens and the endemic Heteropan dolens Druce in Fiji. A synopsis is provided of the cultural, chemical, and biological control programs for L. iridescens in Fiji. In addition, evidence for extinction of L. iridescens and H. dolens is examined through an analysis of little-known literature and neglected museum records. It is suggested that the reason for lack of reports of L. iridescens after 1956 was due to the declining value of copra, which resulted in less research on coconuts; the recall from Fiji of entomologists that worked on the L. iridescens control program by the Imperial Bureau of Entomology; and the subsequent increased abundance of another leaf-trenching lepidopteran, Agonoxena argaula Meyrick, which would have made easy detection of low-density L. iridescens populations difficult. To verify the continued presence of L. iridescens and H. dolens in Fiji will require a comprehensive campaign employing visual searches of coconut palm fronds, the use of ground and aerial malaise traps, canopy fogging, and perhaps chemical analysis of unidentified lepidopteran pupal cocoons found on the thatch of coconut fronds for comparison with chemical profiles of known L. iridescens cocoons. Levuana iridescens Bethune-Baker (Figure 1A) is known only from Fiji, an archipelago of approximately 300 islands in the South Pacific. Levuana is a monotypic zygaenid genus containing one described species, iridescens Bethune-Baker, 1906. Levuana iridescens is a purple moth that was first recorded as a serious coconut pest around 1877 from a single island, Viti Levu, in Fiji. Earlier records on coconut production from 1846 and 1860 do not indicate any severe and widespread maladies affecting palms, especially those caused by obvious and attractive Lepidoptera (Simmonds 1924). On Viti Levu, after 1877, outbreaks of L. iridescens were frequent and devastated coconut palms because feeding moth larvae trenched the underside of leaves, which promoted defoliation and subsequent palm mortality. As a consequence, copra (i.e., dried coconut meat from which coconut oil is extracted) production was severely affected and coconut cultivation bePacific Science (2006), vol. 60, no. 4:439–453 : 2006 by University of Hawai‘i Press All rights reserved 1 Manuscript accepted 25 January 2006. 2 Department of Entomology, University of California, Riverside, California 92521 (phone: 909-787-4714; fax: 951-827-3086; e-mail: [email protected]).