Tricholeon relictus Hölzel & Monserrat , 2002

Acevedo, Fernando, Badano, Davide & Monserrat, Víctor J., 2014, The larva of Tricholeon relictus Hölzel & Monserrat, 2002 a synanthropic antlion (Neuroptera, Myrmeleontidae), Zootaxa 3835 (3), pp. 364-370 : 365-369

Tricholeon relictus Hölzel & Monserrat, 2002

(Figs. 1–4)

Examined specimens. S Spain, Granada: La Herradura, Punta de la Mona, 4 first instar larvae obtained from a female collected 24.VIII.2011, born 11.IX.2011, F. Acevedo & V. J. Monserrat leg.; same locality, 2 third instar larvae and 1 second instar larva laboratory-reared to the third instar, reached 10.IX.2013, D. Badano, F. Acevedo and V. J. Monserrat leg.; same locality, 5 first instar larvae obtained from a female collected VIII.2013, born 19.IX.2013, F. Acevedo and V. J. Monserrat leg., presently kept in their natural site.

Description of 3rd instar larva. Medium sized antlion larva (Table 1). General colouring very pale, whitish (Fig. 1), dorsal side of head capsule very pale ochre with a dark area in proximity of the base of the mandible and with small median markings on the clypeo-labrum and after the frontal sutures, a further pair of small markings are present in the occipital area (Fig. 2), ventral side of the head unmarked (Fig. 3), ocular tubercles black, mandibles dark reddish brown, setae on the dorsal side of the body and on the setiferous processes black while the setae disposed on the lateral and ventral sides are mainly pale brown (Fig. 1).

TABLE 1. Average size measurements (mm) of examined 3rd instar larvae of Tricholeon relictus (3 specimens) and Dendroleon pantherinus (2 specimens). The size range (min–max) of sclerotized body parts is reported after mean. Abbreviations: body length (excluding mandibles) BL, head length HL, head width HW, mandible length ML, ratio head capsule width/length HW/HL, ratio mandible length/head capsule length ML/HL.

FIGURE 1. Tricholeon relictus Hölzel & Monserrat, 2002 , 3rd instar larva, live specimen ( Spain: Granada, La Herradura, Punta de la Mona). A: dorsal view, B: ventral view, C: lateral view.

FIGURES 2–7. Morphological comparisons between 3rd instar larvae of Tricholeon relictus Hölzel & Monserrat, 2002 and Dendroleon pantherinus (Fabricius, 1787) . 2. T. relictus , dorsal view of the head. 3. T. relictus , ventral view of the head. 4. T. relictus , VIII and IX urites. 5. D. pantherinus , dorsal view of the head. 6. D. pantherinus , ventral view of the head. 7. D. pantherinus , VIII and IX urites. Scale bar: 1 mm.

Head. Sub-rectangular in shape, longer than wide (Figs. 2, 3); anterior margin of the labrum with a small median incision; antennae very long and thin, composed by at least 14 flagellomeres; dorsal side of the head covered with dolichasters, paler in proximity of the mouthparts; mandible upturned but relatively straight, similar in length to the head capsule, equipped with 3 pairs of comparatively large teeth; 2–3 pseudo-teeth interspersed with at least 4 dolichasters between the base of the mandible and the basal tooth, 0–2 setae between the basal and median teeth, no setae between the median and apical teeth; external margin of the mandible with a group of stout setae at the base; labial palps elongated, basal segment covered by brown dolichasters (Fig. 3).

Thorax. Pronotum covered with sparse and relatively stout pale brown setae (Fig. 2); mesothoracic spiracles not borne on tubercle; mesonotum with a conspicuous median tuft of hair-like, pale brown setae (Fig. 2), in live specimens a clot of sand grains is retained at its apex; mesothoracic setiferous processes pedunculated, of which the first pair is particularly elongated, metathoracic setiferous processes sub-pedunculated (Fig. 2).

Legs. Pale in colour, covered with black and stout setae on the ventral side.

Abdomen. Dorsal series of setiferous processes bearing stout black setae; abdominal spiracles very small, not prominent; ventral side of the abdomen covered with light brown hair-like setae; IX abdominal sternite longer than wide, covered with long setae interspersed with hair-like ones (Fig. 4).

Differences between larval instars. As typical of myrmeleontid larvae, striking morphological differences are not observable between the first and later instars excluding size, therefore the diagnostic characters are always evident. Anyway the first instar larva is covered with a much sparser setation and the body cuticle is remarkably hyaline.

Ecological notes. T. relictus is a Spanish endemism so far only known for a small coastal area characterized by a very mild and relatively humid climate, situated south of Granada: La Herradura and the neighbouring mount of Cerro Gordo. The type locality of the species is the residential area of Punta de la Mona in La Herradura, a hill site with sparse buildings interspersed with extensive gardens and remnants of the original Mediterranean vegetation, composed by open woods of Aleppo pine with thick undergrowth. The larvae were collected in the foundations of a house located in this site, in a peculiar situation resembling a cave, as this room communicates with the exterior only by small openings thus creating a dark, moist and warm microhabitat characterized by constant conditions ( Monserrat 2010; Monserrat & Acevedo 2011). Despite the obvious artificial origin of this place, a notable resemblance to the natural caves of the area is evident in the geological substratum and overall characteristics. The foundations harbor a rich fauna of synanthropic arthropods of which some represent potential prey for Tricholeon larvae such as: Isopoda Oniscoidea, Collembola Arthropleona, Zygentoma Lepismatidae, Psocoptera , Coleoptera Lathridiidae , Lepidoptera Tineidae and Hymenoptera Formicidae while Diplopoda and Coleoptera Tenebrionidae are improbable due to their hard cuticles; various cohabiting predators have been observed, including Chilopoda Scutigeridae , Araneae Dysderidae and Scythodidae, Opilionida, Coleoptera Carabidae and Hymenoptera Vespidae ( Monserrat & Acevedo 2011) . The presence of T. relictus in this site, though apparently surprising, is not occasional as it is confirmed by 21 empty cocoons discovered. Despite accurate field research the larvae have still not been detected in the natural caves of the area, as potentially suggested by the ecology of the African congeners.

Behavioural notes. Tricholeon larvae are ambush predators as the other members of the tribe. The larvae usually lay where the dust layer is thin, allowing to anchor themselves to the substrate and enhancing their camouflage covering the body with soil debris. They are normally very motionless, often remaining immobile for long periods in laboratory conditions and they are able to feign death for several minutes if disturbed, nevertheless they are agile climbers.

Comparative remarks. The larvae of Tricholeon show the typical set of characters of most Dendroleontini : upturned mandibles, small but prominent ocular tubercles, mesothoracic tuft of hair-like setae and elongated IX abdominal sternite. The larval stages of southern African species T. hirtellus and T. nigripes differ from the closely related genera Dendroleon and Cymothales for the very long and thin anterior mesothoracic setiferous process ( Mansell 1988; Stange 2004). According to Stange (2004), they are also distinguishable from Dendroleon because the median tooth of the mandible is shorter than mandibular width at its insertion. Remarkably the larva of T. relictus is much more similar to Dendroleon than to African congeners in both characters, as the anterior setiferous process is no more than three times longer than wide and the median tooth is noticeably longer than mandibular width.

Comparison with Dendroleon pantherinus . D. pantherinus is a widespread species in central and southern Europe, though generally highly localized. Notably this antlion has never been reported from the Iberian Peninsula despite its presence there is actually possible, especially in the northern half, as suggested by the presence of this species in Mediterranean woody biotopes in Italy ( Badano & Pantaleoni 2014; Badano pers. obs.). The larva of this species remained poorly known despite its early description ( Brauer 1867) and it has been deeply treated only recently by Badano & Pantaleoni (2014). As underlined above, the larvae of T. relictus and D. pantherinus are noticeably similar in overall morphology, differing in relatively minor details. D. pantherinus is a proportionally larger species than T. relictus and it is also evident in the dimensions of the larvae (Table 1). T. relictus is instead characterized by comparatively stouter jaws. In D. pantherinus , one interdental mandibular seta is present between the median and apical teeth (Fig. 5) while it is always absent in T. relictus . Regarding body colouring both species are very pale, whitish antlion larvae but in D. pantherinus the head capsule is much more pigmented, with a typical reddish hue (Figs. 5, 6) while T. relictus shows median dark markings in the anterior part (Fig. 2). The colour of the setae is diagnostic: in D. pantherinus all the setae of the body are blackish, while in T. relictus the stouter setae on the dorsal side of the body and on the setiferous processes are black but the hair like setae (mainly ventro-lateral in position) are pale brown; this difference is immediately evident observing the tuft of hair-like setae on the mesonotum: black in the first species (Fig. 5) and pale brown in the second (Fig. 2). On the contrary, IX urite does not show remarkable differences between the two species (Figs. 4, 7).

From an ecological point view both species are specialized sit-and-wait predators in dark, protected environments. D. pantherinus is typically associated with tree holes but it is also able to colonize different microhabitats, including human buildings ( Gepp 2010; Badano & Pantaleoni 2014); as other species of Dendroleon are also cave dwellers ( Stange et al. 2003) the larvae of this antlion may be at least potentially found in caves or similar environments.