The Castniid Palm Borer, Paysandisia archon (Burmeister, 1880), in Europe: Comparative biology, pest status and possible control methods (Lepidoptera: Castniidae)

Paysandisia archon (Burmeister, 1880) is a Neotropical species of Castniidae recently introduced into Europe (from Argentina), where it has become a serious pest of palm trees. Since it was first reported in Catalonia (Spain) in March 2001, it has also been found in the Comunidad Valenciana and the Balearic Islands (Spain), several Departments in southeastern France, Italy (Sicily, Campania, Lazio, Marche) and even in Sussex (U.K.). Its life history and life cycle were not known in detail previously and are presented here, comparing them with those of other castniid pests, mainly Telchin licus (Drury, 1773), Castniomera atymnius (Dalman, 1824) and Eupalamides cyparissias (Fabricius, 1776). The egg of P. archon (usually 4.4–5.2 mm long) is fusiform, resembling a rice grain, bearing six to eight raised longitudinal ridges which have associated aeropyles along their length, with the micropyle at one end of the long axis; hatching occurs after 12–21 d, according to temperature. Larvae are endophagous; cannibalistic (even affecting prepupal larvae within their fully formed cocoons), mostly as a result of territoriality; undergo unusual lethargic periods and make "false cocoons", most likely to confuse predators/parasitoids; generally go through nine instars (occasionally seven or eight), increasing dramatically in size (from ca. 0.7 cm to 9 cm), and in so doing have considerable destructive power. The total larval stage is quite long, ca. 10.5 months in larvae having a one-year cycle and ca. 18.5 months in larvae having an almost two-year cycle. Larvae can be found tunnelling in different parts of the palms, which largely depends on the larval size, although always on/near the top (crown) of the palm; they will normally not abandon their palm host until the adult stage is reached. The prepupal larval stage is long and complex, made up of two periods. The first occurs before making the cocoon and its length is very variable. The second occurs after the cocoon has been built and includes the time spent by the larva inside the cocoon before converting into pupa; this time is around 17 d in early spring although it can be shortened to only 9 d in early summer. The cocoons (av. length 5.8 cm) are stout with inner walls smoothly coated by a layer of silk and mucus and outer walls loosely covered by fragments of palm fibres which makes them very cryptic. Pupae formed in the second half of March took an average of 66 d to complete their metamorphosis to adults; those formed in the first half of April took 52 d; those formed in the first half of July took 43 d. The adult moths are day-flying insects. ♂♂ (which occur slightly less abun-dant than ♀♀, in the ratio of 1:1.19) are very territorial and fly in hot, sunny weather. Their flight is very powerful, rapid and darting (an estimation would be 20 m/s), being able to hover for a few seconds; the flight path is generally straight although right/left shifts are frequent and the moth can be seen balancing its body accordingly. They fly over and over rather small areas, returning to the same perching places. Their orientation skills are extraordinary; being capable of flying hundreds of meters, disappearing from human sight for several minutes and coming back exactly to the same palm leaf they had taken off from. In the lab, ♀♀ lived an average of 14.1 d whereas ♂♂ lived 23.8 d, and both sexes do not appear to feed at all in this stage. Preliminary research indicates that sex recognition seems to be visual at first. ♀♀ simply move around within the appropriate habitat until they are spotted by a patrolling ♂, in much the same way as butterflies do. The fact that electroantennograms carried out using ♀ ovipositor (hexane) extracts, triggered a positive and significant response in ♂ antennae, seems to indicate that P. archon has at least a ♀-released short-range pheromone for conspecific sex recognition, while ♀-released long-range pheromone, i.e. that used by other heterocerans to attract conspecific ♂♂ at longer distances, might be absent in P. archon and replaced by visual attraction. Mating in the wild has been observed and described for the first time. ♀♀ lay eggs singly (through their long extensible ovipositor) in a very quick and inconspicuous manner; most eggs are found within the fibre webs closest to or within the palm crowns; they are not glued to the fibres, remaining loose within their thick layers (1–2 cm inside). Dissected virgin ♀♀, known to have laid no eggs, were found to have about 140 eggs. As for the life cycle, adults appear in the wild in mid-May and disappear in late September, with a peak during June and July; sightings of adults in May, August and September are much rarer. Live eggs are expected to be found from late May to mid-October. The larval stage is the longest and most complex of all P. archon stages. It is the only one that overwinters; during winter time, nearly all instars can be found within the palms in the wild, including prepupal ninth instar larvae. Most larvae will undergo a one-year cycle, although a second group will experience an almost two-year one. Live cocoons can be found from mid-March to mid-September. In summary, the P. archon life cycle in Catalonia comprises, from egg to egg, an average of 389 days (i.e. 12.8 months) in specimens undergoing a one-year cycle and an average of 673 days (i.e. 22.1 months) in specimens undergoing a two-year cycle. P. archon larvae seem to be specialized feeders on Arecaceae (palm trees) as all reported hostplants fall within this monocotyledonous family; however, within it, the larvae are unspecified feeders, given the variety of genera they attack. As to natural enemies, in Europe as well as in the Neotropics, there are no factual data as yet; however some empty eggs have been found in the wild in Catalonia strongly suggesting the attack by a hymenopterous egg parasitoid or an egg-predacious hemipteran. Very cold winter temperatures lasting for several consecutive days might increase mortality in the overwintering archon larval population sheltered in palm trees; notwithstanding that, this pest has proven to be well adapted to the Mediterranean climate. Symptoms of infestation by P. archon on palms are (1) presence of sawdust on the palm crown and/or palm trunk; (2) presence of perforated or nibbled leaves (non specific); (3) presence of gallery holes (axial and transversal) within the palm trunk (observable when the palm trunk is cut in slices); (4) abnormal development of axillary leaf buds; (5) deformation and abnormal twisting of palm trunks; (6) abnormal drying up of the palms, especially the core leaves. As for possible measures of control, so far, only those using chemical insecticides have been tested (apart from pulling-up and burning the infested palms); good results were obtained by wetting the palm crown and trunk with contact and/or systemic organophosphorus insecticides (Chlorpyrifos, Acephate and Dimethoate); best results were obtained by using Chlorpyrifos 48%, dose 200 ml/Hl or Acephate 75%, dose 150 g/Hl.