Rotastruma stenoceps Bolton

Ying Y. Luo & Benoit Guénard, 2016, Descriptions of a new species and the gyne in the rarely collected arboreal genera Paratopula and Rotastruma (Hymenopytera: Formicidae) from Hong Kong, with a discussion on their ecology, Asian Myrmecology 8, pp. 1-16 : 12-13

Rotastruma stenoceps Bolton

Material examined. An individual collected in HONG KONG, Lung Fu Shan Country Park, at N 22.279139 E 114.136755, elevation 273m, hand collected at approximately 21:00 h, 21.iv.2016 (Ying Y. LUO), label “ANTWEB1009015” deposited at SBSHKU.

Female description

Material examined. HL 0.72 mm; HW 0.85 mm; MaL 0.41 mm; SL 0.59 mm; EL 0.25 mm; WL 1.21 mm; PNW 0.62 mm; PNH 0.48 mm; MW 0.56 mm; SPL 0.31 mm; PTL 0.61 mm; PTW 0.28 mm; PTH 0.31 mm; TL 4.33 mm; PPL 0.31 mm; PPW 0.28 mm; PPH 0.30 mm; CI 85; SI 81; MaI 56; PI 46; PPI 118

Head. In full face view, head rectangular in shape, slightly wider than long (CI 85). Posterior margin of head straight and posterior corners of head rounded as in worker (see figure 15 in Bolton 1991). Sides of head straight and parallel. Eyes large, in the longest dimension with a dozen ommatidia. Median ocellus level with the posterior margin of the compound eye. Frontal carinae extending to the occipital margin. Mandibles triangular, masticatory region of mandibles with 6 teeth. Antenna with 12 segments and terminated with a 3-segmented club.

Mesosoma. In profile view, dorsum of mesonotum broadly rounded. Propodeal spiracle round and near the anterior margin of the metapleural gland bulla. Wing scars clearly visible. Propodeal spines slightly downcurved, almost straight, apically acute, and marginally extending beyond the propodeal lobes. In dorsal view, mesosoma longer than wide, with anterior margin longer than the posterior margin.

Metasoma. In profile view, petiole pendunculate with an ill-defined node, postpetiole roughly square in shape. A small denticle is present on the ventral side of the penducle, located near the propodeum. In dorsal view, petiole rectangular in shape, and postpetiole trapzedoidal in shape, with anterior margin of postpetiole shorter than the posterior margin. No sting visible.

Sculpture. Cuticle thick, all surfaces except for the antenna, legs, penduncle and gaster sculptured. Frons with distinct parallel lines of sculpture. In profile view, sides of mesosoma laterally costate. In dorsal view, scutum and scutellum laterally costate, petiole and postpetiole rugose to rugose-reticulate. Ventral sides of peduncle conspicuously smooth First gastral tergite smooth, with some short basigastral costulae.

Pubescence. All dorsal surfaces of head, mesosoma and metasoma with short sub-erect, apically acute hairs, gold in colour. Antenna with abundant hair, oriented to the apex. Coxa, femur and tibia covered in short suberect hairs, oriented towards the tarsus. Subpostpetiolar process with a few thin erect hairs.

Colouration. Whole body a uniform goldenbrown colour, mandibles slightly darker in colouration. Gaster darker, light-brown.

Castes. For worker description refer to Bolton (1991). Male caste is unknown.

Distribution

Rotastruma stenoceps is known from Hong Kong and the following Chinese provinces: Guangdong, Hubei, Hunan and Yunnan.

Ecology

Very little is known of the ecology of Rotastruma . The specimen was found walking on a railing adjacent to a hiking trail at approximate 21:00 h. The surrounding area of the hiking trail is a monoculture plantation of the tree Lophostemon confertus Wilson & Waterh. Whether or not R. stenoceps is actually nocturnal is unknown at this point because the female may have performed a nuptial flight earlier in the day and could have been looking for a suitable location to start a colony.

Remarks

Previously, two worker specimens of R. stenoceps were found in Hong Kong in past studies, both with features as described by Bolton (1991).

In general, the morphology of the queen is similar to the worker, as discussed by Bolton (1991), unless otherwise stated.

This specimen is distinct from R. recava and is similar to R. stenoceps due to the following features: lack of concave occipital margin, sides of head with projecting hairs, relatively straight propodeal spines and propodeal spiracle near the metapleural gland bulla.