Strongylognathus testaceus

This species is a slave-maker and is only found in nests with its hosts and. It occurs in a range of habitats including steppe habitats and pine forests in Russia (Zryanin & Zryanina, 2007).

Identification
Yellowish brown. Head rectangular with pronounced occipital emargination and postero-lateral angles. Body shining with long fine pale hairs present also on appendages. Sculpture variable, with longitudinal striae present or more or less effaced on head and alitrunk. Length: 2.0-3.6 mm (Collingwood 1979).

Distribution
Pyrenees to Ukraine, North Italy to Sweden (Collingwood 1979).

Distribution based on Regional Taxon Lists
Palaearctic Region: Andorra, Austria, Belarus, Belgium, Bulgaria, Croatia, Czech Republic, Georgia, Germany, Greece, Hungary, Iberian Peninsula, Lithuania, Netherlands, Poland, Republic of Moldova, Romania, Russian Federation, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkmenistan, Ukraine, United Kingdom of Great Britain and Northern Ireland.

Biology
Collingwood (1979) - This species occurs only in the nests of its host Tetramorium caespitum. Workers and brood of both host and parasite are present but only the sexuals of Strongylognathus are developed, the original Tetramorium queen as well as the adoptive Strongylognathus queen usually being found present together.

S. testaceus workers are normally greatly outnumbered by Tetramorium workers. Observations on this and related species suggest that neighbouring nests of the host species are raided to recruit more Tetramorium pupae to the colony which is often very populous with up to 20,000 individuals. Alatae are present in July and August.

Guillem et al., 2014 - S. testaceus is a degenerate slave-maker of Tetramorium caespitum and T. impurum. The Strongylognathus queen does not kill the host queen, but instead pheromonally inhibits production of the host sexual brood. As the number of parasite workers rarely exceeds 1%, they rarely (or perhaps never) raid additional colonies for extra slaves (Sanetra and Gusten, 2001; Czechowski et al., 2002; Tinaut et al., 2005). Thus, this species may be considered an intermediate stage between slave-makers and inquilines.

Strongylognathus testaceus were collected from two colonies of Tetramorium c.f. impurum and a single colony of T. semilaeve in the Catalan Pyrenees, Spain during June 2011. Colonies were found under stones. The colony found with T. semilaeve contained S. testaceus sexuals (both males and females). Within Iberia, S. testaceus has only been recorded from T. caespitum and T. impurum (Tinaut et al., 2005), so this is also the first record of S. testaceus with T. semilaeve. Approximately one in 50 colonies of Tetramorium was parasitized.

Guillem et al. (2014) examined cuticular hydrocarbon (CHC) profiles between this parasite and its hosts. They found that the parasitic species had CHC profiles that were indistinguishable from that of their hosts, even when the parasite is using more than one host species. The level of chemical mimicry even extended to the more subtle between-colony differences in profiles. In all cases the profiles of un-parasitized colonies were similar to those that were parasitized indicating that it is the parasites that have adjusted their profile to match that of their host and not vice versa. This explains why these social parasites are fully integrated members of each colony and are treated as nest-mates.

It should be noted that in some species, for example Harpagoxenus sublaevis (Winter and Buschinger, 1986), raiding workers are frequently killed or driven off when trying to raid or invade new host colonies, since they are carrying their own host colony odour, which is likely to be different from that of the one they are raiding. This is why parasites continue to use a wide range of other chemical and morphological adaptations associated with their parasitic lifestyle. These include a thickened cuticle and production of appeasement or propaganda compounds (e.g. Allies et al., 1986; Lloyd et al., 1986; Ollett et al., 1987; D'Ettorre et al., 2000). These tactics allow the parasite time to make the necessary adjustments to its profile. Acquiring a host profile may be possible in just a few hours (R. Kather, pers. comm., cited in Guillem et al. (2014)).

Nomenclature

 *  testaceus. Eciton testaceum Schenck, 1852: 117 (w.q.m.) GERMANY. Combination in Strongylognathus: Mayr, 1853d: 390. Senior synonym of emarginatus: Mayr, 1853d: 390; of diveri: Brown, 1955c: 113. See also: Baroni Urbani, 1971c: 151; Kutter, 1977c: 166; Atanassov & Dlussky, 1992: 156; Sanetra, Güsten & Schulz, 1999: 343.
 * emarginatus. Myrmus emarginatus Schenck, 1853: 188 (w.) GERMANY. Junior synonym of testaceus: Mayr, 1853d: 390.
 * diveri. Strongylognathus diveri Donisthorpe, 1936c: 113, figs. 1, 2, 7 (w.) GREAT BRITAIN. Junior synonym of testaceus: Brown, 1955c: 113.