Tapinoma, Foerster, 1850

Seifert, Bernhard, Kaufmann, Bernard & Fraysse, Lorenzo, 2024, A taxonomic revision of the Palaearctic species of the ant genus Tapinoma Mayr 1861 (Hymenoptera: Formicidae), Zootaxa 5435 (1), pp. 1-74 : 45-46

Tapinoma magnum Mayr 1861 [type investigation]

The species has been described from Pisa, Italy. Investigated was the lectotype male labelled “Savi Pisa”, “ T. nigerrim. Magnum det. Mayr ” [both labels in Mayr’s handwriting], “ Lectotype Tapinoma magnum ( MAYR, 1861) des. SEIFERT 2012” and “AntWeb CASENT 0915547”. One paralectotype gyne on another pin labelled “Savi Pisa”, “ T. nigerrim. Magnum det. Mayr ” [both labels in Mayr’s handwriting] and “ Paralectotype Tapinoma magnum ( MAYR, 1861) des. SEIFERT 2012”. Both specimens are stored in NHM Wien. The allocation of the two type specimens to the corresponding species cluster was shown by Seifert et al. (2016) .

Material examined. Numeric phenotypical data were taken in 122 nest samples with 375 workers. They originated from Algeria (10 samples), Austria (1), Azerbaijan (1), Belgium (1), France (27), Great Britain (2), Germany (27), Greece (5), Italy (32), Morocco (7), Netherlands (4), Spain (1), Switzerland (3) and Tunisia (1). For details see supplementary information SI1, SI2 .

Geographic range. Tapinoma magnum has by far the widest distribution among the three supercolonial species of the T. nigerrimum group. It is easily spread through transport of potted plants and trees over the Mediterranean which already should have happened during the time of the Roman Empire with materials coming over from Africa. This complicates the assessment of the natural range of origin. Yet, it seems that range expansion started from North Africa and South Italy and reached North Italy and southernmost France. The colonization of South England, North France, the Benelux countries, Germany, Switzerland, and Austria is a very recent phenomenon. It started in about 1990 as a consequence of the intensification of international trade with rapid road transport and the mood of northern citizens to place big pots of Mediterranean plants in their gardens and court yards. The near absence of T. magnum from Spain (only one site south of Seville known) and rarity in the French Mediterranean coast is probably explained by strong competition through T. ibericum and T. darioi . It is puzzling that no findings are known so far from Asia Minor and the East Mediterranean. According to current state of information, the colonization of a city park in Baku / Azerbaijan appears to be an outlier. The altitudinal distribution of 122 nest sites is 134 ± 211 [-15, 1509] m with 97% of the findings made below 600 m.

Diagnosis:—Worker ( Tab. 3): All shape ratios given below are, in contrast to those in Tab. 3, primary ratios without RAV and all data are given as arithmetic mean ± standard deviation. Large, CS 963 ± 148 µm. Head broad CL/CW 1.049 ± 0.057. Postocular distance rather small and excavation of hind margin of vertex large, PoOc/CL 0.374 ± 0.012, ExOcc 1.81 ± 0.97%. Anteromedian clypeal excision less deep than in related supercolonial species and rather wide, ExCly/CS 8.72 ± 1.03%, ExClyW 6.64 ± 0.73%. The posterior, semicircular end of clypeal excision forms a concave plane delimited by a sharp ventral and a blunt dorsal edge. Sum of pubescence hairs and smaller setae protruding across the margin of clypeal excision including its dorsal edge very large, nExCly 15.1 ± 5.6. Scape longer than in related supercolonial species, SL/CS 0.968 ± 0.041. Minimum distance of the inner margins of antennal socket rings larger than in related supercolonial species, dAN/CS 0.310 ± 0.008. Eye moderately large, EL/ CS 0.256 ± 0.013. Metanotal groove deeper than in related supercolonial species, MGr/CS 4.20 ± 0.90%. Mesosoma rather long and wider than in related supercolonial species, ML/CS 1.291 ± 0.030, MW/CS 0.644 ± 0.019. Second funiculus segment longer than in related supercolonial species, Fu2L/CS 14.79 ± 0.47%, IFu2 1.928 ± 0.092. All body parts including appendages covered by a rather dense pubescence. Setae on dorsal and lateral surfaces of head and mesosoma absent. Longe seta are found on hind margin of 3rd and 4th gaster segment, ventral parts of coxae and anterior clypeus. All body parts blackish brown. Mandibles and edge of clypeus sometimes with an orange or reddish color component.

Taxonomic comments. The very clear phenotypical and genetic separation from other species of the T. nigerrimum group has been shown above ( Figs. 44 , 45 ).

Biology. The following combined properties of T. magnum imply a big invasive potential in urban or ruderal areas of Central Europe: (a) sufficient frost resistance, (b) the quick development of local dominance due to supercolonial life style and fighting techniques (c) a broad food spectrum which is additionally extended by worker polymorphism, (e) intranidal mating and (f) a physiological potential for long-range dispersal flight and independent single-queen colony foundation. Considering that all populations in England, the Benelux countries, Central Europe and in France north of 45.8°N have been founded by anthropogenous introduction, T. magnum had a share of 75.5% within 49 introduced populations, followed by T. ibericum (16.3%) and T. darioi (8.2%). The most important beachheads for introduction are garden centers and tree nurseries followed by botanical gardens. It became an important pest in settlements by digging up large amounts of sand from under pavements and kerbs, and by affecting garden plants through promotion of trophobionts. In the Netherlands it also forages in houses, ascending to the upper floors ( Van Boesschoten et al. 2017). Colonies survived in Germany cold winters including a 14-days frost period with mean air temperatures of -6.6°C and an absolute minimum of -15°C without any visible damage. In the Mediterranean particularly abundant in open unstable or degraded areas with significant to very strong anthropogenic influence and a weakly developed tree layer. Typical for coastal areas and frequent in city centers. It prefers more sandy soils and is less abundant on rock. If reports from S France ( Bernard 1968, 1983), should largely refer to T. magnum, it shows a quite developed tolerance against flooding, occurs in high numbers on irrigated clay soils in areas of market gardening and is found even in swampy habitats. Rather outstanding appears the high-altitude population in the Djurdjura National Park / Algeria (36.463°N, 4.178°E, 1509 m) that was found in an open situation with Juniperus , Ilex and Rosa within a mixed Pine-Cedar-Oak forest. Density data are missing. In the Mediterranean it is locally an eudominant species accounting for 95% of ants in some sites. Nests are subterranean and often very extended, frequently reaching to a depth of 1 m. Nest entrances typically develop to big crater-like domes of ejected soil particles (Seifert 2018). Nesting also in basements of buildings. Colonies usually develop big supercolonies stretching over areas of up to 20 hectares with millions of workers and a permanent exchange of brood between the nests via above-ground trails and subterranean tunnels. Single nests may contain up to 350 queens. Alates were observed in Algeria, Italy, France, Germany and the Netherlands 7 May ± 27 d [2 Apr, 23 Jun] n=11—this is apparently the main period. Swarming occurred in May and June, not earlier than 2–3 weeks after eclosion from pupae. Alates were also observed in August to September. Most mated gynes stay in or near to the home colony seeking adoption in conspecific nests but their big bodies and well-developed flight muscles indicate a potential ability for long-range dispersal flight and independent colony foundation. One flight observed in the Netherland 31 May 2014 took place 9:23 h Solar Time ( Noordijk 2016). The German and Dutch populations ( Heller 2011, Noordijk 2016) showed the last activity in late December at 3°C air temperature (cloudy days) or -2°C (sunny days). Activity was resumed after snowmelt in January at mean and maximum air temperatures of 10.6 and 12.2°C (cloudy days) or at maximum temperatures of 6.5°C during a sunny day. T. magnum was observed in Italy to cause severe injuries in horseradish plants in order to imbibe phloem sap (Seifert 2018). similar observations were made on tomato and zucchini stems and leaves in France. It rears root aphids in large numbers, which allows it to thrive in open, grass-dominated parks, gardens and semi-natural habitats (repeated pers. obs. of Kaufmann). T. magnum is known from Corsica and S France to limit the spread of the invasive Linepithema humile . In space and food competition assays, T. magnum was more efficient in both interference and exploitative competition, clearly superior in direct fight, dominated food in 100% of the replicates after 1h and invaded Linepithema nests while the reverse was never observed ( Blight et al. 2010). Tapinoma magnum is potentially superior to any ant species of open land but the final winner is determined by both fighting and recruiting properties as well as ecological adaptation and demographic factors. The displacement from food sources by Pheidole pallidula has to be seen in this context. The investigations of Pavan & Trave (1958) on highly toxic anal gland secretions, attributed by them to Tapinoma nigerrimum and later referenced by Blum & Hermann (1978) under the same name, were obviously not done in this species because of the Italian collecting site and because the enormous mass of ants (“environ 15 kg d ‘ouvrières”) used for the chemical analysis could only be harvested from a supercolony. Most probably the species under study was Tapinoma magnum which is according to our data more abundant in the region of Pavia than T. darioi . Blum & Hermann (1978) suggested that the iridodials, which can polymerize rapidly, may serve as carrier or fixative for the more volatile ketones in the secretion thus increasing their toxicity. Strong intraspecific aggressivity between polydomous colonies of T. magnum in garden centers of Germany suggests repeated introductions to the same site but artificially isolated colony fragments developed a significant aggression between former nest mates already 6 months after separation (Seifert 2018). Protection of vine and citrus mealybug colonies by T. magnum significantly reduced the effect of several parasitoids and predators with the exception of adult Coccinellidae ( Mansour et al. 2012) .

Figures

FIGURE 44. Separation of worker nest sample means of Tapinoma ibericum (black dots), T. darioi (white triangles) and T. magnum (white squares) by a linear discriminant function considering 12 RAV-corrected phenotypical characters.

FIGURE 45. Comparison of the NUMOBAT-based classification of five species of the Tapinoma nigerrimum group with the genetic classification based on 15 microsatellite loci. Method: the first four principal components extracted from microsatellite data of 805 samples were used as characters in a linear discriminant function with the NUMOBAT-based classification imposed as species hypothesis. T. nigerrimum (white rhombs), T. magnum (black squares), T. darioi (crosses), T. hispanicum n. sp. (white dots) and T. ibericum (black dots).