Paysandisia archon (South American palm borer)

There are two pathways of accidental introduction:

1) the commercial import of palms (Arecaceae) originating from areas where the pest occurs; this is probably the main pathway by which the pest spreads over large distances as it can often go undetected (international level).

2) the movement of palm trees from a contaminated area to an area free from the pest (national level).

The adult moth is a long-distance flier (Sarto i Monteys and Aguilar, 2005). If an infested palm is sold to an end consumer in a region where there are very few other palms present, it is unlikely that the pest could establish in that region.

There is very little information in the literature on P. archon in its native area mainly because it isn’t a pest in its native range. This may be because it lives on wild palm trees and natural enemies limit its populations. The only available publication is a short note which contains some biological information (Bourquin, 1933). In Europe P.archon adults appear in mid-May and disappear in September-October, with a peak in abundance during June and July. P. archon males are very territorial and powerful fliers. They fly repeatedly over rather small areas, returning to the same perching place. Long range sex recognition appears to be mediated by visual attraction. It is possible to observe all stages of the pest (eggs, larvae, pupae and adults) during the summer. The adult moths emerge and are active during the hottest part of sunny days. Eggs are laid between the palm fibres, either singly or in a small cluster. The average number of eggs laid in the wild is not known but could be around 140 on the basis of observations on female dissections by Sarto i Monteys and Aguilar (2005). The larvae start looking for food immediately after hatching, and shelter and bore into the host plants. The larvae are endophagous for most of their lives, with only the first instar being partly or fully exophagous. P. archon overwinters as larvae and all larval instars can be found in the palms during winter. Consequently some larvae, generally those hatched early in the season, overwinter once, whereas others will overwinter twice. Cocoons with living pupae can be found from mid-March to mid-September. Larvae can be found tunnelling in different parts of the palms. Early-instar larvae can be found in the stype, within the fruit of C. humilis, or within the leaf rachis (especially in Phoenixcanariensis and Washingtonia filifera). For example, in Trachycarpusfortunei, the first-instar larvae can bore into the young, packed palm leaves. This chewing becomes very obvious later, as the leaf develops, opens and expands, showing a series of consecutive holes on a circular section. Large larvae will only be found in the stype. They tend to bore into and remain within the very core of these structures, where the humidity is higher and the temperature more stable. The cocoon is always located on or near the surface of the stype or leaf axil. The cocoon remains in a cavity at one end of the terminal larval gallery (Riolo et al., 2005; Sarto i Monteys and Aguilar, 2005).

P. archon larvae are specialized feeders on palm trees (Arecaceae). Although they have a well-developed proboscis, P. archon adults have never been seen feeding in the wild or in captivity (Miller, 1986; Sarto i Monteys and Aguilar, 2005).

P. archon is native to north-western Argentina, Brazil (Rio Grande do Sul), Paraguay (Paraguayan Chaco) and western Uruguay (Miller, 1986; Lamas, 1995; Sarto i Monteys and Aguilar, 2005).

In its native range the moth lives on Butia yatay, Trithrinaxcampestris and Syagrus romanzoffiana in the ecosystems where these palm species occur. T. campestris is a south American palm native of Uruguayan and north-eastern Argentine savannas and also extends to the summits of mountain ranges of Sierras de Córdoba and Sierras de San Luis. B. yatay is native of Argentina, southern Brazil and Uruguay and grows in arid savannas in subtropical or temperate climate with soft summers and cold winters. S. romanzoffiana is indigenous to southern and south-eastern Brazil, eastern Paraguay, north-eastern Argentina and northern Uruguay, where it grows in monsoonal forests and swampy areas, always at low altitudes. T. campestris and B. yatay are present in Uruguayan savanna. The Uruguayan savanna, also known as the Brazilian-Uruguayan savanna, is a subtropical grassland and savanna ecoregion which includes all of Uruguay, some areas of north-eastern Argentina and southernmost Brazil. The Uruguayan savanna ecoregion extends from the extreme southern part of Rio Grande do Sul, Brazil, to include the entire country of Uruguay, and a small section of the Argentinean province of Entre Ríos. These savannas encompass a mosaic of gallery forests, palm savannas and outcropping of submontane forests. Annual precipitation in the area ranges from 1000 mm in the southern part to 1300 mm in the northern part. The average temperature is 16^°C in the south and 19^°C in the north. This large ecoregion is relatively flat, ranging from sea-level to altitudes of about 500 m in some areas (McGinley, 2007).

P. archon could be a threat to the subtropical species Phoenix canariensis which is native to the Canary Islands, and to the two European palm species Phoenix theophrasti and Chamaerops humilis (Montagud Alario, 2004). In the coastal regions of the eastern Canary Islands, where many species are related to the flora of Sahara desert, P. canariensis is part of the natural vegetation. P. theophrasti is native to Greece (Crete) and Turkey (registered on the IUCN Red List of Threatened Species) (Johnson, 1998). C. humilis is distributed along the Mediterranean Basin, which stretches from Portugal east to Jordan and from northern Italy south to Morocco and includes parts of Spain, France, the Balkan states, Greece, Turkey, Syria, Lebanon, Israel, Egypt, Libya, Tunisia and Algeria, as well as around 5000 islands scattered around the Mediterranean Sea (Caley, 2008).

There are no reports on the impact on biodiversity caused P. archon in its current area of distribution.

P. archon is listed in the EPPO A2 List of ‘Pests recommended for regulation as quarantine pests’. As P. archon cannot readily be detected in consignments of young palms, phytosanitary measures to prevent its introduction should concentrate on ensuring the absence of the pest at the place of production. The following possibilities have been considered: origin from a pest-free area, origin from a pest-free place of production (since at least 2 years), plants produced under suitable protected conditions (e.g. under a net), or various combinations of these measures. In addition, countries in which P. archon is already present should apply phytosanitary measures to suppress and contain existing outbreaks (OEPP/EPPO, 2008).

According to Council Directive 2000/29/EC all imported consignments of plants and plant products requiring a Phytosanitary Certificate have to be inspected by the Plant Protection Services in order to prevent the introduction of harmful organisms with the imported commodities.

Eradication is difficult because the larvae develop within the host plant for 1-2 years. Also, the adult moths can fly away. Economically speaking, eradication measures are expensive and in some cases imply the destruction of the host plant/s.

The biological characteristics of P.archon make its control difficult (the larvae is endophagous except for a very short time from eclosion to entering the host plant). As P. archon is not a pest in its native range, no control methods have been developed there.

An original approach proposed by scientists at the French National Institute for Agricultural Research (INRA) consists of coating the sensitive part of the stype with a glue that acts as a physical barrier between the tree and P.archon (Peltier, 2007).

P. archon is listed in European Phytosanitary Legislation in AnnexII/Part A/Section II (COMMISSION DIRECTIVE 2009/7/EC of 10 February 2009 amending Annexes I, II, IV and V to Council Directive 2000/29/EC on protective measures against the introduction into the Community of organisms harmful to plants or plant products and against their spread within the Community) as ‘Pests, known to occur in the European Union, whose introduction into, and/or whose spread within all European Union member States is prohibited, with reference to specific plants or plant products’: ‘Plants of Palmae intended for planting having a diameter of the stem at the base of over 5 cm and belonging to the following genera: Brahea, Butia, Chamaerops, Jubaea, Livistona, Phoenix, Sabal, Syagrus, Trachycarpus, Trithrinax, Washingtonia’.It is required an official statement (Annex IV, Part A, Section I)that plants: (a) have been grown throughout their life in a country where P. archon is not known to occur; or (b) have been grown throughout their life in an area free from P. archon, established by the national plant protection organisation in accordance with relevant International Standards for Phytosanitary Measures; or (c) have, during a period of at least 2 years prior to export, been grown in a place of production:

- which is registered and supervised by the national plant protection organisation in the country of origin, and

- where the plants were placed in a site with complete physical protection against the introduction of P. archon or with application of appropriate preventive treatments, and

- where, during three official inspections per year carried out at appropriate times, including immediately prior to export, no signs of P. archon have been observed.

Preventive and curative field trials carried out in Italy and Spain in order to evaluate the efficacy of the entomopathogenic nematode Steinernema carpocapsae showed a very high efficacy (Sanchez and Clemente, 2007; Martinez de Altube and Martinez Peña, 2009; Nardi et al., 2009).

Laboratory trials with a strain of the entomopathogenic fungus Beauveria bassiana (strain Bb 147) have been conducted in France and have shown good results (Millet et al., 2007; Besse-Millet et al., 2008).

Good results were obtained in Spain by wetting the palm crown and stype with contact and/or systemic chemical insecticides (Sarto i Monteys and Aguilar, 2005). In Italy, the Marche Plant Protection Service observed that foliar applications of chemical insecticides over a 3 year period (2005-2007) had difficulty reaching endophagous P. archon larvae (Nardi et al., 2009). Tree injections of insecticides have also been used against this pest in Europe (Reid and Moran, 2009).

It should be stressed that the availability of products containing these active substances varies nationally. In addition it is difficult to develop insecticide treatments that can be used on palms in public areas (parks and gardens).