Allomerus decemarticulatus

The workers of Allomerus decemarticulatus construct a trap for capturing prey that is built from plant material and fungi.

Identification
Fernández (2007) - Besides the 10 segmented antennae, this species can be distinguished by its mesosomal shape in lateral view, in which the propodeum forms a weak angle between the faces. The petiolar shape (peduncule longer than the node) and the near lack of sculpture on the mesopleuron and lateral propodeum also makes this species easy to recognize. The anteroventral tooth of the petiole is larger than that of other workers of the genus. Almost the entire body (except for the propodeum) possesses long hairs that are longer than the last antennomere.

Distribution based on Regional Taxon Lists
Neotropical Region: Brazil, Ecuador, French Guiana.

Biology
Fernández 2007:

Wheeler (1942) reports an A. decemarticulatus collection made on expanded Hirtella peduncles and another (probably) on Tococa or Duroia, both from Brazil. Dejean et al. (2001) cite monogynous colonies of A. decemarticulatus in Hirtella physophora (Chrysobalanaceae), with populations of more than 1.000 workers, which patrol leaves during the day, searching for prey. The Allomerus material reported by Kempf (1975:347) as A. decemarticulatus could be Allomerus brevipilosus, if there is species fidelity to the associated plants.

Recently Dejean et al. (2005) described trap construction to capture prey. The ants cut trichomae from the plant in which they live (Hirtella physophora), and use them to build a kind of a net on which a mycelium grows. The resulting construction is a platform-like structure with holes on it, on which the fungus grows. This platform works as a trap for jumping or flying insects that stand on it and are attacked by the ants from below. The holes have exactly the right diameter to let the ants’ heads and anterior legs pass (Corbara 2005). Dejean et al. (2005) suggest that this is a type of tripartite association (insect- plant- fungus) with the object of ambushing prey.

There is another queen from French Guiana, Petit-Saut collected by B. Corbara and coworkers in June 9th, 2000 (No. 5299, deposited in CEPLAC) and with a label that states “dans nid Allomerus 10-articulatus/Hirtella 4”. It is a dealate female and was collected in an apparently normal nest in terms of the population, including the queen itself.

This specimen is very similar to what is here described as an A. decemarticulatus queen, although the virtual lack of erect pilosity raises attention. There are short hairs on the head, propodeum and ventral surface of the gaster, but the rest of the body can be considered as glabrous. Taking into account both queens (one described above) which were seen and referred to this species, plus the data provided by Kempf (1975:347), it can certainly be established that the A. decemarticulatus queen has moderate to dense pilosity. The glabrous queen collected in an A. decemarticulatus nest provides the bases to speculate about polygyny or symbiotic processes (parasitism) mentioned by Hölldobler and Wilson (1990). This interesting finding will be explored in further publications.

Nomenclature

 *  decemarticulatus. Allomerus decemarticulatus Mayr, 1878: 874 (w.) BRAZIL. Kempf, 1975c: 347 (q.). See also: Fernández, 2007a: 164.

Fernández (2007) - The holotype was not seen. The redescription should be used cautiously because the original description is based on French Guiana queen and worker samples, in which worker possesed 10 segmented antennae. There is a worker from the MZSP (HW 0.50 HL 0.55 SL 0.28 WL 0.50 GL 0.55 TL 2.03 CI 90 SI 56) collected in Brazil (Amazonas, Manaus, Fazenda Esteio, Colosso, mata continua controle, 26 nov to 1 dic 1997, C. Klingenberg col.) with a 10 segmented antennae. This worker is smaller than the one studied from French Guiana and the propodeum is less angulate and does not show the angulation.

Although Kempf (1975:347) provides some data for the queen, he does not describe it, so the actual description has missing information.

Worker
Fernández (2007) - (n=1): HW 0.55 HL 0.58, 0.60 SL 0.33 0.55 WL 0.58 GL 0.54 TL 2.20 CI 94 SI 60.

Antennae 10 segmented, scapes fail to reach posterior lateral corner of head, distal half thickened. Metanotal suture shallow and broad. Propodeum unarmed, dorsal face almost absent followed by declivous face, slightly angulate between faces. Propodeal spiracle small. Petiole with peduncle and with node well defined, node shorter than peduncle. Petiolar anteroventral spine well developed. Sides of mesopleuron and propodeum with few longitudinal short and irregular carinulae. Hairs abundant on dorsum of mesosoma. Long hairs (greater than 0.13 mm in length): six on front of dorsum of head, near vertexal margin and decumbent; two rows of several hairs on frons; several on promesonotum, none on propodeum, several on petiole, postpetiole and gaster. Short hairs (less than 0.07 mm) on all the dorsum of the mesosoma, few are present on propodeum. Row of short hairs present on the anterior clypeal margin, central being the longest, all projecting over anteclypeus. Antennae and legs with apressed pubescence. Concolorous brownish yellow, hairs whitish.

Queen
Fernández (2007) - Head longer than wide, eyes prominent. Antennae 11 segmented without defined club. Scutellum forms slight prominence with convex dorsal part in lateral view. Propodeum angulate between faces. Propodeal spiracle open laterally. Petiolar node shorter than peduncule; peduncule and node broadly joined. Anteroventral process of petiole acute and without tooth or spine. Smooth and polished body. Head with longitudinal striae especially on posterior part. Longitudinal rugulae on posterior part of mesoscutum. Axilar transverse band and scutellum with dense and conspicuous longitudinal striation. Propodeum with limited striation, obliquelly longitudinal below propodeal spiracle. Pilosity abundant on body (length of hairs less than antennal width), except on most of mesoscutum, anepisternum and katepisternum. Concolorous brown with black eyes and axillae.