Labiotermes Holmgren

Constantino, Reginaldo, Acioli, Agno N. S., Schmidt, Karen, Cuezzo, Carolina, Carvalho, Sérgio H. C. & Vasconcellos, Alexandre, 2006, A taxonomic revision of the Neotropical termite genera Labiotermes Holmgren and Paracornitermes Emerson (Isoptera: Termitidae: Nasutitermitinae), Zootaxa 1340, pp. 1-44 : 4-6

Genus Labiotermes Holmgren

Cornitermes (Labiotermes) Holmgren, 1912: 50

Labiotermes Holmgren in Sjöstedt 1926: 150 [part]; Emerson & Banks 1965 [revision]; Mathews 1977: 207 –208 [redescription]

Type­species: Cornitermes labralis Holmgren , designated by Sjöstedt (1926: 150).

New synonym: Paracornitermes Emerson (in Snyder 1949: 333). Type­species: Cornitermes laticephalus Silvestri, 1901 ; Mathews 1977: 203–207 [redescription].

Etymology: Holmgren (1912) does not mention the etymology. Based on his diagnosis, the name Labiotermes apparently comes from the Latin word labium, lip, and refers to the enlarged labrum of the soldiers of some species, especially L. labralis .

Imago. Head capsule rounded. Eyes medium to large. Ocelli conspicuous. Fontanelle triangular, eliptical or elongate. Postclypeus moderately to strongly inflated; median line conspicuous. Mandibles similar to workers, except that the molar plate is narrow. Antennae with 16–18 articles. Pronotum almost as wide as head with eyes. Tibial spurs 2:2:2.

Soldier. Monomorphic or dimorphic. Head capsule large and subrectangular in dorsal view. Frontal tube short, never reaching the labrum. Antennae with 15–16 articles. Labrum long, tongue­shaped, with convex sides and a hyaline tip. Mandibles robust. Left mandible with two marginal teeth, large in some species and vestigial in others. Right mandible with one or two marginal teeth close to its base. Pronotum with strongly raised anterior lobe. Meso­ and metanotum with a row of minute spines on lateral margins. Front coxa with or without a lateral projection near base. Front and middle femur with numerous short and thick bristles on dorsal side. Tibial spurs 2:2:2.

Worker. Monomorphic. Head capsule light colored. Abdomen very large and transparent, showing dark gut content. Left mandible: left mandible index 0.8–1.4; M1 large and conspicuous; M2 absent; M3 smaller than M1; cutting edge between M1 and M3 sinuous; distance from M3 to M4 more than half the distance from M1 to M3; M4 hidden under the molar prominence in dorsal view. Right mandible: M1 large and conspicuous; M2 small; molar plate wide and concave, without ridges. Antennae with 15–16 articles.

Pronotum with strongly raised anterior lobe. Meso­ and metanotum with a row of minute spines on lateral margins. Front coxa with or without a lateral projection near base. Front and middle femur with numerous short and thick bristles on dorsal side. Tibial spurs 2:2:2.

Gut morphology (worker). Crop small. Mixed segment with one large and one small mesenteric lobe (the small one is vestigial in L. brevilabius ). Malpighian tubules inserted in two pairs at the junction of mesenteron and proctodeum, between the mesenteric lobes. Proctodeum very large. First segment (P1) strongly dilated, about the same size as the third (P3 or paunch). Enteric valve wide. Armature with 1–6 ridges of irregular sizes covered with short and straight or long and curved, hair­like spines.

Comparisons. Labiotermes belongs to a group which also includes Syntermes , Procornitermes and Cornitermes . They share similar soldiers, with more or less rectangular head capsule, short frontal tube and strong mandibles, and similar gut morphology. Soldiers and workers of Labiotermes can be readily identified by the presence of a line of minute spines on the lateral margins of both the meso­ and metanotum. The imagos of 4 species of Labiotermes remain unknown, and the same is true for several species among the related genera. The imagos of Syntermes have antennae with 19–21 articles and their tibial spurs are 3:2:2. The imagos of both Syntermes and Cornitermes have mandibles with short apical teeth and conspicuous molar ridges. The imagos of Procornitermes are more difficult to distinguish because some species have antennae with 15–16 articles and mandibles without molar ridges. They can be differentiated by the narrower gap between M3 and M4 on left mandible. Armitermes and Embiratermes are heterogeneous, probably non­monophyletic genera and the imagos of many species remain unknown. They are generally smaller and have antenna with 15 articles, but the mandibles of their imagos are very similar to those of Labiotermes .

Remark 1. The new synonymy is justified because these species comprise a relatively small, very uniform and clearly monophyletic group. The separation of Paracornitermes from Labiotermes was based only on the larger teeth of soldier mandibles of the former. The dentition of soldier mandibles, however, can be quite variable between different species of the same genus ( Fig. 11 ) and often shows significant intra­specific variation.

Remark 2. Neither Holmgren (1912) nor Emerson & Banks (1965) presented a diagnosis or formal description of Labiotermes , and the original description of Paracornitermes was very brief. Araujo (1954) redescribed Paracornitermes in a little more detail. The most detailed previous descriptions of both genera were those presented by Mathews (1977), who argued that they should be merged into a single genus.

Remark 3. The following species were previously included in Labiotermes but are clearly unrelated: Cornitermes corniferous Sjöstedt , Cornitermes rhinoceros Sjöstedt and Ceratotermes valens Silvestri ( Holmgren 1912; Sjöstedt 1926). Their soldiers are superficially similar to those of Labiotermes , but the worker morphology show a completely different pattern ( Sands 1998). Snyder (1949) lists these African species in the genus Ceratotermes, subfamily Termitinae . The taxonomic position of Ceratotermes is discussed by Emerson (1952: 481–482), who argues that it is not related to Labiotermes . Later, Krishna (1963) transferred these three species to the genus Foraminitermes Holmgren.

Remark 4. Labiotermes and Paracornitermes have been included in Nasutitermitinae by most previous authors. Engel & Krishna (2004) transferred Labiotermes to their new subfamily Syntermitinae , which also includes Syntermes , Cornitermes and Procornitermes . However, they did not mention Paracornitermes nor the other 9 genera of mandibulate nasutes ( Armitermes , Cahuallitermes , Curvitermes , Cyrilliotermes , Embiratermes , Ibitermes , Macuxitermes , Noirotitermes and Rhynchotermes ). The phylogenetic relations of the mandibulate nasutes are not clear ( Donovan et al. 2000), and according to Miller (1986) they form a paraphyletic group. In our opinion, the separation of these 4 genera in a new subfamily is not a satisfactory solution. Three questions remain unanswered: 1) are the mandibulate nasutes a monophyletic or paraphyletic group? 2) is subfamily Nasutitermitinae monophyletic or polyphyletic including the mandibulate nasutes? 3) how are Syntermes , Cornitermes , Procornitermes , and Labiotermes related to the other 9 genera of mandibulate nasutes? In any case, the removal of these four genera from Nasutitermitinae will not solve any real problem nor improve the classification.

Habits. All species of Labiotermes are humivores and live either in savannas or forests. Their workers have large abdomens and particles of mineral soil are easily visible in the gut content. The nest of L. labralis is arboreal, while the nests of the other species are subterranean, or sometimes found inside termitaria built by other species, such as Cornitermes spp.

Geographic distribution. Labiotermes occurs in most South American countries, with a southern limit near 26S. It also occurs in Trinidad, but does not reach Central America. The absence of records from Ecuador is certainly due to limited sampling.

Economic importance. There are a few records of Labiotermes spp. present in agricultural systems (e.g. Calderon & Constantino, in press), but there is no direct observation of damage. Since they are humivores, they are certainly not structural pests.

Figures

FIGURES 11. Soldier mandibles. A, Labiotermes brevilabius; B, L. emersoni; C, L. guasu, new species; D, L. labralis; E, L. laticephalus; F, L. leptothrix; G, L. longilabius; H, L. oreadicus, new species; I, L. orthocephalus; J, L. pelliceus. Scale bars = 0.5 mm.