X. Espadaler and H. Cagniant.
Plagiolepis xene Stärcke, the first inquiline ant from the Balearic Islands (Spain).
Psyche 98(4):351-354, 1991.

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PLAGZOLEPIS XENE STARCKE, THE FIRST INQUTLINE ANT FROM THE BALEARIC ISLANDS (SPAIN)
Parasitic ants (sensu Wilson, 1971) are rarely found though they seem to be fairly abundant when searched for specifically (Buschinger, 1987). Populations of these peculiar ants seem to be highly dispersed; this implies little gene flow between widely sep- arated populations. If this is generally the case it would potentially lead to increasing speciation rates. The taxonomy of Mediterranean Plagiolepis has not been revised since Santschi (1920) and Emery (1921) and recent findings suggest that new species remain to be described. A new species with apterous males and females, has been found in El Hierro, Canary Islands (unpublished) and three new parasitic Plagiolepis, two from Morocco, one from the Iberian Peninsula are currently being described (in prep). These discover- ies imply that parasitic Plagiolepis may be found wherever poten- tial host species are abundant.
The ants from the Balearic Islands have been extensively stud- ied (Saunders, 1901, 1904; Wheeler, 1926; Bernard, 1961 ; Comin & De Haro, 1980; Comin & Espadaler, 1984; De Haro et al., 1986; Comin, 1988), but no inquiline species have ever been reported. During a short visit (2.5 working days) we found three populations of P. xene Starcke, parasitic on P. pygmaea (Latr.). Plagiolepis xene was found at the following three sites: Station 1. Puig d'es Nogue, Mallorca, Spain. April 30, 1991. Grazed fire cut. 830m, NW slope with small flattened places with sparse vege- tation of Smilax aspera, Asphodelus, Hypericum, Astragalus, Teucrium, Gladiolus and some isolated Pinus halepensis. (1). Department de Biologia Animal, Biologia Vegetal i Ecologia. Universitat Autonoma de Barcelona. 08193 Bellaterra. Spain. (2). Laboratoire d'Entomologie. Universite Paul Sabatier. 118, route de Narbonne. 3 1062 Toulouse. France.
Manuscript received 18 November 1991.




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352 Psyche [vo~. 98
Plagiolepis pygmaea and P. xene were found under medium sized stones. Other ant species present (in order of abundance): Tetramo- rium semilaeve, Lasius niger, Tapinoma nigerrimum, Pheidole pal- lidula, Aphaenogaster subterranea, Hypoponera eduardi. Station 2. km 57 on the road from Seller to Deya, Mallorca, Spain. May 1, 1991. 200m. Pine wood on steep slope facing NW. Underwood of Ampelodesma mauritanica, Cistus mospeliensis, Cistus albidus, Erica rnultiflora, Rhamnus, Asparagus, Lotus tetra- phylus. Other ant species present: Lasius niger, Leptothorax "specularis", Camponotus sicheli, Camponotus scutellaris, Crem- atogaster laestrygon, Messor bouvieri.
Station 3. km 60 on the road from Deya to Valldemosa. Mal- lorca, Spain. May l, 199 l. 350m. Dense evergreen-oak forest; fee- ble slope facing NW-W. Very sparse underwood of Arbutus unedo, Ruscus aculeatus, Smilax aspera, Asparagus, Daphne, Cyclamen. Other ant species present: L. recedens, Lasius alienus, A. subter- ranea, C. scutellaris, P. pallidula, Colobopsis truncatus, Lasius niger and Hypoponera eduardi. It is worth mentioning that in the huge population of Leptothorax recedens no Epimyrma species was recovered.
During collection parasitic females could be detected because, as stones were turned over, they were always surrounded by a group of host workers. Several females were found in each group but no males were present in any nest at the time of collection. At Station 1 the host population was sufficiently dense to allow a ten- tative study of frequency of parasitization. Censuses made in four distinct places, several hundred meters apart, indicate that the par- asites are extremely localized. They occupy a restricted surface of some 100 m2, thus showing an extremely contagious distribution. Single parasitized nests under medium sized stones were found in Station 2 (out of three host societies found) and Station 3 (out of four host societies).
Our P. xene collections were compared with Iberian samples. No morphological differences were detected in palps, mandible, pilosity and hypopygium. Likewise, no differences were detected between host specimens and Iberian P. pygmaea specimens.



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19911 Espadaler & Cagniant 353
Though it is widely distributed (but rare) in France, Italy, Spain and Central Europe, the P. xene on Mallorca are most likely to have derived from populations on the Iberian Peninsula. Isolation of the Balearic Islands can be dated to the Messinian (Azzaroli and Guazzone, 1980; Hsu et al. 1973), some 5-5.5 million years BP, when Majorca was still in contact with the Iberian Peninsula. The Balearic populations of P. xene inhabit biotopes that are not undisturbed or completely natural and, therefore, they cannot be considered relict populations. On the Iberian peninsula (unpub- lished data) samples of this species also come from the rather dis- turbed biotopes. This ant may be an exception to the usual rule that parasitic species are found in long-term stable, undisturbed biotopes. Because of this association with disturbed habitats, it is possible that P. xene has been imported to the Balearics in rela- tively recent times. A similar case of an imported inquiline ant has been reported for Anergates atratulus Schenck in North America (Brown, 1957) and it is interesting to note that both Plagiolepis pygmaea (host to P. xene) and Tetramorium caespitum (L.) (host to A. atratulus) inhabit more or less disturbed habitats. Plagiolepis xene Starcke is the first inquiline ant reported from the Balearic Islands. Parasite populations may have become estab- lished in the Balearics relatively recently since they do not occur in undisturbed habitats.
To Prof. A. Buschinger for interesting suggestions; to Drs. J. Resell, C. Llompart and J. Pons for useful comments on Balearic origins and Andrew Jones and an anonymous referee for correc- tions on the text.
AZZAROLI, A. AND GUAZZONE, G.
1980. Terrestrial mammals and land connections in the Mediterranean before and during the Messinian. Palaeogeogr. Palaeoclim. Palaeoecol. 29: 155-167.




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