Small Réunion Swallowtail: Papilio phorbanta

IUCN Red List Conservation Status: Vulnerable

Papilio phorbanta, the Papillon La Pature, is protected by law on the island of Réunion where it is now endemic, having been extinct in the Seychelles since 1890. Without adequate protection of its habitat and foodplants the species could still be very seriously threatened, despite the legislation. Surveys of its habitat and designation of protected areas are urgently required.

Description

This beautiful short-tailed butterfly in the nireus species-group (10) has a forewing length of 40-55mm. The male is black and blue and the female is brown with white markings (6, 11) (Plates 8.1 and 8.2). This difference between the sexes is unique in the nireus species group (4), and may be caused by mimicry of Euploea goudotii (Danainae) (7).

Male: UFW/UHW black with a broad median band and blue spots. LFW/LHW ground colour blackish brown becoming yellowish at the wing margins, with whitish submarginal spots (11).

Female: UFW/UHW red-brown with white submarginal spots (2, 11). LFW/LHW brown with a pale grey marginal band, black triangular spots and a grey mark on the hindwing (2, 11).

Distribution

This species is now endemic to the island of Réunion, a French Overseas Department 900km east of Madagascar in the Indian Ocean (11). The much smaller subspecies nana Oberthür is known only from a single pair from the Seychelles and is believed to be extinct since 1890 (6).

Habitat and Ecology

Réunion is a volcanic island with a remarkable topography. The highest point is 3069 m above sea level and 61 percent of the land surface is at altitudes over 1000 m. Because of the altitude and ruggedness of the terrain, large areas of upland vegetation remain unaffected by man. In the lowlands however, virtually no forest remains. Papilio phorbanta is a forest-dwelling butterfly which, like other members of the nireus species group, feeds on Rutaceae. The 4cm long green or yellow-green caterpillars (11) are nowadays usually found on Citrus trees, to which the species has apparently adapted. The 3cm long pupae are known to be collected and raised in captivity for commercial purposes. P. phorbanta has long used Citrus as a food source, having been recorded in garden fruit trees by Manders in 1908 (7) and by Boisduvalas long ago as 1833 (1, quoted in 5). However, the extent of its present colonization of Citrus groves has not been reported.

Threats

It has been suggested that the pair of Papilio phorbanta nana from the Seychelles was either artificially introduced or wind-blown from Réunion (2, 6), but in view of the unusually small size of the pair, such a provenance seems unlikely. Although the origin of the subspecies was probably Réunion, the small size suggests a lengthy period of isolated evolution and natural selection. In the absence of further evidence there is no reason to suppose that nana was anything but a rare subspecies of P. phorbanta, now extinct for unknown reasons. Such an event may act as a warning to prevent the same fate for the nominate subspecies on Réunion. Well into the 1950s Papilio phorbanta was still common on Réunion (13). However, with the rapidly expanding human population, more and more land has been turned over to agriculture, mainly for sugar (9). Although this has caused severe reductions in the butterfly’s range, there are still significant areas of upland forest on Réunion, theoretically protected due to the rugged relief (13). Evergreen rainforest still covers a large belt around Piton des Neiges (3069 m) and Piton de la Fournaise (2631 m) (9). Réunion is the largest and still the least ecologically disturbed of the Mascarene islands, but deforestation continues, often in favour of reafforestation with Japanese red cedar (Cryptomeria japonica). A number of vertebrates have become extinct in the 300 years since human settlement (9) and there is no reason to suppose that many invertebrates have not disappeared also. The ability of the larvae of P. phorbanta to feed on Citrus trees might be expected to ensure the butterfly’s survival even in the face of destruction of its natural forest habitats, but three factors mitigate against this. Firstly, feeding on Citrus is no insurance against destruction because of the stringent insecticidal measures taken against species that are regarded as pests of that crop. Secondly, there is a suspicion that the introduction of a parasitic tachinid fly 10-15 years ago to control the caterpillars of P. demodocus may have also taken a toll of P. phorbanta (13). Thirdly, P. demodocus itself may competitively exclude P. phorbanta from the Citrus groves, as it is suspected of doing for P. manlius on Mauritius. Papilio demodocus, like P. demoleus, is an aggressive butterfly that actively chases other species (2). Even were these fears to prove unfounded, it is quite unacceptable for wild species to decline so far that they are only able to survive as a minor pest of man’s agricultural labours.

Conservation Measures

In recognition of the increasing threat to the species the French Ministers of Environment and Agriculture declared on 22 August 1979 that P. phorbanta would henceforth be a protected species (8). The decree outlawed the destruction or removal of eggs, caterpillars, pupae and adults and forbade trade in the species. Such legislation has served to draw attention to the plight of P. phorbanta, but failed to have any impact in the more important matter of protecting the butterfly’s natural habitat or food plants. In addition, it has not encouraged much-needed biological studies, nor facilitated ranching or farming of specimens for release into the wild. According to reports on the ground, there is currently no conservation effort being made on behalf of this species, which is seen less and less.

References

1. Boisduval, J.B.A.D. de (1833). Faune Entomologique de Madagascare, Bourbon et Maurice. Paris.
2. D’Abrera, B (1980). Butterflies of the Afro tropical Region. Lansdowne Editions, Melbourne, xx + 593 pp.
3. Dove, H. (1983). In litt., 18 April.
4. Hancock, D.E. (1983). Classification of the Papilionidae (Lepidoptera): a phylo genetic approach. Smithersia 2: 1-48.
5. Hancock, D.E. (1983). In litt., 21 June.
6. Legrand. H. (1959). Note sur la sous-espèce nana Ch. Oberthür de Papilio phorban Linné des iles Seychelles [Lep., Papilionidae]. Bulletin de la Société Entomologique de France 64: 121-123.
7. Manders, N. (1908). The butterflies of Mauritius and Bourbon. Transactions of the Entomological Society of London 1907: 429-454.
8. Ministère de l’environnement and Ministère de I’agriculture (1979). Liste des insectes protégés on France. Journal Officiel 22 August: 93-94.
9. Moutou, F. (1984). Wildlife on Réunion. Oryx 18: 160-162.é
10. Munroe, E. (1961). The classification of the Papilionidae (Lepidoptera). Canadian Entomologist Supplement 17: 1-51.
11. Paulian, R. and Viette, P. (1968). Faune de Madagascar. XXVll Insectes Lépidoptères Papilionidae. O.R.S.T.O.M. and C.N.R.S., Paris. 97 pp.
12. Smart, P. (1975). The Illustrated Encyclopedia of the Butterfly World. Hamlyn, London. 275 pp.
13. Viette, P. (1983). In litt., 6July.

This page has been transcribed and edited, with permission, from Threatened Swallowtail Butterflies of the World: the IUCN Red Data Book by N.M. Collins & M.G. Morris. Whilst providing a sound baseline of information, it is in need of updating. The full volume, with references, may be downloaded from the IUCN Library System.