Importation of Mature Palms: A Threat to Native and Exotic Palms in Mediterranean Countries?

Taxonomy
The scientific name for this moth is Paysandisia archon Burmeister; it belongs to the family Castniidae (Lepidoptera), most members of which live in South America.

Description
The adult is a beautiful moth, with a large wingspan of 9–11 cm. The fore-wings are olive brown-coloured and the hind-wings are brightly coloured with red, black and white (Fig. 1). The antennae are clubbed. Females are a little larger and are easily recognizable by their chitinous ovipositor at the end of the abdomen. The eggs are laid separately; they are oblong (5 mm long), cream-coloured and with longitudinal ribs (Fig. 2). Just after hatching, the larva is pink-coloured and less than 1 cm long, but turns white as it grows. It reaches 6–7 cm at the end of its development, looking a bit like a grub, and with four pairs of pseudopods (Fig. 3).

Geographical distribution
The moth is native to the central region of Argentina and neighboring Uruguay where it lives on palms, Trithrinax campestris among other species. Trithrinax campestris grows in the wild on the plateau of the central northern part of Argentina (east of Cordoba) where up until the present is very common. However, as shown in Gibbons’ paper (2001), this palm (el Caranday) seems now to be threatened in its native country. There is a huge need for agricultural land in Argentina, and so T. campestris has to be eliminated as land is cleared for fields. For this reason, a great number of them are burned or at best uprooted for commercial purposes. They are exported to other countries, such as in Europe, where they are first put together in the same site before they are sold and spread to other north Mediterranean places.

In France, Paysandisia archon is presently localized in the Department of Var, between Toulon and Hyères (Fig. 4) where it has been introduced most probably with imported Trithrinax from Argentina. It is also recorded in Spain, in the area of Girona (Catalonia) with the same probable origin (Aguilar 2001). Until now, no record has been officially reported in other Mediterranean countries, although it is likely to be present in Italy as well. It arrived in France a few years ago (probably about 1995) but its presence was not notified at that time and the official record with accurate scientific identification was only made in July 2001 (Drescher & Dufay 2001). With the increasing interest in palms in all the towns of the south of France, it is likely that the dispersal range of this pest will enlarge to other areas of the region in the near future.

Biology
Very few data are available on P. archon in the literature. The main reason is that it is not considered as a pest in its native country, probably due to the presence of natural enemies (parasites and predators), which limit its populations, but also to the fact that it lives originally on palm trees growing naturally and not on crops. Its life cycle has not been studied in Argentina. Only one author, F. Bourquin, has written a small paper with some biological information on this moth, in an Argentinian journal (Bourquin 1933).

The few observations made in France suggest that the moth has a long cycle of development. The adults are observed from June to September. They are active during the day. All stages of development, from egg to chrysalis have been recorded at the same time, in July. The egg is laid at the basis of the leaf on the stem or in the terminal bud. The larva bores a gallery (Fig. 3) through the stem or through the young leaves, not yet expanded at the stem apex (in the terminal bud), causing characteristic damage (Fig. 5). When several larvae bore simultaneously in the stem, the palm becomes weak (Fig. 6) and can even die. Except for the period when the adults are flying, it is difficult to detect the presence of the pest; at the larval stage the only sign may be the presence of plugs of debris, like sawdust, visible at the outermost extremity of the gallery (Fig. 7). The larva turns into a chrysalis, protected by a cocoon made with palm fibres (Fig. 8), inside the gallery. At the very end of its development, the chrysalis frees itself from the cocoon at the outermost extremity of the gallery, and a new adult moth is born after tearing this envelope. The remains of the chrysalis are often attached to the exit hole of the gallery for a while.

Damage
In Argentina, P. archon was reported to attack native palms such as Trithrinax campestris and Butia yatay, as well as occasional exotic species such as Latania, Chamaerops or Phoenix canariensis (Bourquin 1993). In France, the moth appears to have a large range of hosts and can damage many different palms besides T. campestris, for example Chamaerops humilis, Livistona chinensis, L. decipiens, L. saribus, Sabal spp., Phoenix canariensis, P. dactylifera, P. reclinata, Trachycarpus fortunei and Washingtonia filifera. This list is probably not exhaustive and will have to be added to following other future observations. In Spain, it has been observed on Trachycarpus fortunei, Phoenix canariensis, Washingtonia spp. and Chamaerops humilis (Aguilar 2001).

The damage is observed at different levels of the tree: leaves, rachis and top of the stem. Once hatched, the larva bores towards the heart of the palm and if several larvae are present on the same tree, this can lead to the death of the palm. Big palms can survive if they are not too severely attacked, but small ones or plants in the nursery or in containers are very exposed to attack. It is this ability to feed on a large variety of palm species that makes this pest a real threat to the future of palms in regions of Europe where it has been accidentally introduced.

Control methods
Unfortunately since this moth is not a pest in its native country, no control method has been developed. Some chemicals must be tested before being allowed to be uses in parks and gardens, but it is not certain how effective they can be in reaching the larva hidden inside the trunk. Biological control (i.e. the use of natural enemies) could be another possibility, safer for the environment, but it needs several years for development.

Conclusion
As far as we know to date, this pest has been observed in only two limited areas (in France and in Spain), but Paysandisia could spread to a much larger region if no severe measures are taken. In France, this pest has been recently included in the list of noxious organisms submitted for compulsory control measures (Official Journal, February 2002). With the large number of palm species susceptible to its attacks, the moth could seriously threaten the palms that represent a large part of the tourist image of the south of France. The international trade in mature palm trees must be severely limited and controlled to prevent pests from being introduced (other exotic pests have been recently discovered on imported palms in France and in the soil around their roots), because this practice can lead to severe damage to already established palms. It is the role of palm lovers to be aware of this serious problem and to act in order that the object of their passion can live safely for many years; any observation of new or suspected damage on trees must be notified to experts.

LITERATURE CITED

AGUILAR, L.L. 2001. A new lepidopteran family for the European fauna. SHILAP Rev. Lepid. 29: 86–88.

BOURQUIN, F. 1933. Notas biologicas de la Castnia archon Burm. Rev. Soc. Ent. Argentina 24: 295.

DRESCHER, J. AND A. DUFAY. 2001. Un nouveau ravageur des palmiers dans le sud de la France. PHM-Revue horticole 429: 48–50.

GIBBONS, M. 2001. Trithrinax, trials and tribulations. Palms 45: 74–79.

JOURNAL OFFICIAL. 21 fév 2002, p. 3371.

LEPESME, P. 1947. Les insectes des palmiers. P. Lechevalier, 903 p.

2. Paysandisia archon: egg.

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3. A larva of Paysandisia archon in its gallery.

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4. Map showing the two main areas of distribution of Paysandisia archon in France and Spain.

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5. Typical damage caused by the larva of Paysandisia archon on a leaf of Washingtonia filifera.

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6. Serious damage to Trachycarpus fortunei caused by Paysandisia archon.

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7 “Sawdust plugs” ejected at the outside of the gallery by the larva of Paysandisia archon (damage on Phoenix canariensis).

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8.  Chrysalis of Paysandisia archon extracted from its cocoon.

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