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1 June 2017 Worldwide Distribution of Syllophopsis sechellensis (Hymenoptera: Formicidae)
James K. Wetterer, Mostafa R. Sharaf
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Abstract

Syllophopsis sechellensis (Emery) (formerly Monomorium sechellense) (Hymenoptera: Formicidae) is a small, inconspicuous ant species, native to the Old World tropics, but has spread by human commerce to other parts of the world. The extent of its original native range is unclear. Here, we examined the worldwide distribution of S. sechellensis, particularly its spread to the New World. We compiled published and unpublished S. sechellensis specimen records from >160 sites. We documented the earliest known S. sechellensis records for 43 geographic areas (countries, island groups, and West Indian islands), including many islands for which we found no previously published records, in Southeast Asia (Singapore), the Indian Ocean (Comoro Islands, Îles Éparses, Mascarene Islands), Pacific Ocean (Palau), Atlantic Ocean (Cape Verde Islands), and the Caribbean (Guadeloupe, Grenada, Martinique, Mona, Puerto Rico, St. Croix, St. Lucia, St. Martin, St. Thomas, St. Vincent, and Trinidad). The geographic ranges of S. sechellensis and other Syllophopsis species suggest that S. sechellensis may be native to Madagascar and neighboring islands in the western Indian Ocean or to Southeast Asia or both. The earliest known record of S. sechellensis in the New World was collected in Barbados in 2003. We recorded this species on 11 additional West Indian islands. This finding might indicate that S. sechellensis is rapidly spreading through the West Indies. Alternatively, it may be that this inconspicuous ant has simply been overlooked or misidentified in this region.

Syllophopsis (Hymenoptera: Formicidae) is a genus of small, inconspicuous ants, with 21 described species (Bolton 2016). Most Syllophopsis species are known only from the Afrotropical bioregion. One Syllophopsis species, however, has achieved broad distribution through multiple bioregions: S. sechellensis (Emery). Here, we examined the worldwide distribution of S. sechellensis, and evaluated where it may be native and where it has recently spread through human commerce.

Santschi (1915) described Syllophopsis as a subgenus of Monomorium. Some subsequent authors followed this designation, whereas others considered Syllophopsis to be a distinct genus. Most recently, Ward et al. (2014) revised the genus Monomorium and confirmed Syllophopsis as a distinct genus.

Syllophopsis workers are small, monomorphic, yellow to light brown in color, and have 12-segmented antennae with 3-segmented terminal clubs (Bolton 1987). Syllophopsis species resemble small Solenopsis thief ants. However, the 2 genera can be distinguished easily because Solenopsis workers have 2-segmented terminal clubs.

Of the 21 recognized species of Syllophopsis, 17 species are known only from the greater Afrotropical region: Africa, Madagascar, the Arabian Peninsula, and western Indian Ocean islands: S. adiastolon (Heterick), S. aureorugosa (Heterick), S. cryptobia (Santschi), S. dentata (Sharaf), S. elgonensis Santschi, S. ferodens (Heterick), S. fisheri (Heterick), S. gongromos (Heterick), S. hildebrandti (Forel), S. infusca (Heterick). S. jonesi (Arnold), S. kondratieffi (Sharaf & Aldawood), S. malamixta (Bolton), S. modesta (Santschi), S. saudiensis Aldawood, S. sersalata (Bolton), and S. thrascolepta (Bolton). In addition, 3 Syllophopsis species are known solely from outside the Afrotropical bioregion: S. subcoeca (Emery) (from the Neotropics), S. australica (Forel) (from Australasia, Indomalaya, and Oceania), and S. vitiensis (Mann) (from Fiji). Only S. sechellensis has been widely reported both from islands of the western Indian Ocean islands and from other parts of the world.

Emery (1894a) described Monomorium fossulatum sechellense (= S. sechellensis) from the Seychelles before Emery (1895) described the nominal subspecies of M. fossulatum from Burma. When Wilson & Taylor (1967) synonymized the 2 subspecies, they designated M. fossulatum as the senior synonym. However, based on the publication dates of the 2 names, Bolton (1995) designated M. sechellense as the senior synonym.

Like most Syllophopsis species, S. sechellensis has tiny eyes. One character, however, that distinguishes S. sechellensis from other members of the genus is that its entire mesopleuron is matte and reticulate punctate, whereas in all other described Syllophopsis species the mesopleuron is glossy and smooth.

Materials and Methods

Using published and unpublished records, we documented the worldwide range of S. sechellensis. We obtained unpublished site records from museum specimens in the collection of the Museum of Comparative Zoology, Cambridge, Massachusetts (MCZ). In addition, we used online databases with collection information on specimens by AntWeb ( www.antweb.org). We excluded records where identifications were recorded as uncertain, e.g., Onoyama (1976) reported “M. fossulatum (?)” from Okinawa, Japan.

We obtained geographic coordinates for collection sites from published references, specimen labels, maps, or geography websites (e.g., earth.google.com,  www.tageo.com, and  www.fallingrain.com). If a site record listed a geographic region rather than a “point locale,” and we had no other record for this region, we used the coordinates of the largest town within the region or, in the case of small islands and natural areas, the center of the region. We did not map records of S. sechellensis on boats, found in newly imported goods, or intercepted in transit by quarantine inspectors.

Published records usually included collection dates. In some cases, records did not include the collection dates for specimens, but we were able to determine or approximate the date based on information from museum specimens, on the collector's travel dates, or limit the date by the collector's date of death. We categorized each site record as belonging to 1 of 7 terrestrial bioregions (following Olson et al. 2001): Afrotropics, Palearctic, Indomalaya, Australasia, Oceania, Nearctic, and Neotropics.

Fig. 1.

Worldwide distribution records of Syllophopsis sechellensis.

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Results

We compiled published and unpublished S. sechellensis specimen records from >160 sites (Fig. 1). We documented the earliest known S. sechellensis records for 43 geographic areas (countries, island groups, and West Indian islands), including many islands for which we found no previously published records, in the Indian Ocean (Comoro Islands, Îles Éparses, Mascarene Islands), Pacific (Palau), Atlantic (Cape Verde), and Caribbean (Guadeloupe, Grenada, Martinique, Mona, Puerto Rico, St. Croix, St. Lucia, St. Martin, St. Thomas, St. Vincent, and Trinidad) (Tables 1 and 2).

Records ranged in lat