Gelis apterus (Pontoppidan, 1763)

Korenko, Stanislav, Schmidt, Stefan, Schwarz, Martin, Gibson, Gary A. P. & Pekar, Stano, 2013, Hymenopteran parasitoids of the ant-eating spider Zodarion styliferum (Simon) (Araneae, Zodariidae), ZooKeys 262, pp. 1-15 : 6-10

Gelis apterus (Pontoppidan, 1763) Figures 5 A–C6A–B

Ichneumon apterus Pontoppidan (1763): 692-693. Holotype female, missing. Comments about description in Schwarz (1995).

Recognition.

Schwarz (2002) gave a key to the western Palaearctic species of Gelis with apterous females, and Schwarz (1995, 1998) provided a diagnosis and description of the female of Gelis apterus . The main diagnostic features of the female are summarised below; the descriptions of the male and pupa are new.

Description.

Female (Fig. 5A). Length 3.2-5.5 mm. Apterous. Body mostly black but base of antenna orange and thorax, propodeum and first segment of gaster varying from entirely black to nearly entirely orange; legs mainly blackish or dark brown with yellowish brown parts; tibiae white basally. Antenna with 21-25 segments; third segment (without anellus) 3.7 –4.4× as long as wide. Malar space 1.2 –1.3× as long as wide. Mesoscutum in lateral view not or only weakly sloping anteriorly, with a strong or weak median longitudinal furrow. Mesopleuron with fine striation anteriorly or more rarely almost entirely striate. Metapleuron entirely granulate or more rarely partly smooth and lustrous. Hind femur 4.0 –4.9× as long as wide. Ovipositor sheath 1.9 –2.5× as long as hind tibia. Ovipositor curved upwards, its tip with only very weak teeth ventrally.

Male (Fig 5 B, C). Length 3.0-4.1 mm. Macropterous. Body mostly black but mandible with teeth reddish, palpi brown, and tegula yellowish brown or brown. Legs with coxae, trochanters, trochantelli and femora except for following black or blackish brown; fore and mid femora yellowish-brown apically; tibiae basally whitish (most distinct on hind tibia), fore tibia except basally, and mid tibia except basally and apically yellowish-brown, hind tibia except basally blackish brown; tarsi brown or blackish brown. Fore wing with pterostigma brown except white basally. Body mostly distinctly granulate and matt, without distinct punctures. Antenna with 21-23 segments; third segment (without anellus) 2.9 –3.3× as long as wide; segments 11-13 with linear tyloids. Clypeus in profile evenly and rather weakly convex, smooth or weakly granulate dorsally in addition to some scattered punctures; lower margin convex and region just above lower margin depressed. Mandible rather long, its teeth of equal length, outer surface with a distinct swelling subbasally. Malar space 1.2 × as long as basal width of mandible, and without a furrow. Genal carina joining oral carina behind base of mandible. Ocelli small. Head behind eyes in dorsal view moderately narrowed and distinctly convex. Pronotum without dorsomedian longitudinal ridge. Mesopleuron with fine granulation and weak rugosity, speculum and hind margin below speculum smooth. Prepectal carina present but rather weak. Propodeum of moderate length and with both transverse carinae complete and distinct; longitudinal carinae anterior to posterior transverse carina rather weak and absent basally except for lateral longitudinal carina; propodeum lustrous between transverse carinae and with longitudinal striation about as distinct as longitudinal carinae; lustrous anterior to posterior transverse carina, nearly smooth and with distinctly separated area petiolaris. Legs slender with hind femur 5.0 –5.1× as long as wide. Fore wing with areolet rather small. Gaster with first segment slender, without median dorsal carinae, and with dorsolateral and ventrolateral carinae rather weak.

Pupa (Fig. 6A, B). Pupa brownish (becoming dark brown as part of sclerotization process), about 5.5-7 mm.

Material.

PORTUGAL, Beja district: 2 ♀ Ribeira de Limas, direction to Guadiana River, slope close to unpaved road (37°51'N, 7°31'W, Fig. 2, locality 4), 24.v.2011, S. Korenko leg. (1 pupa and 1 larva), larva on Zodarion styliferum , pupated 25.v.2011, adults emerged 5.vi.2011 and 7.iv.2011. Specimens deposited in collection of M. Schwarz.

Évora district: 1 ♂ Montemor o Novo, surrounding of castle ruins (38°38' N, 8°13'W, Fig. 2, locality 1), 10.iv.2010 (pupal stage), S. Korenko leg., adult emerged 12.iv.2010. 1 ♀ Monsaraz, olive grove (38°26' N, 7°32' W, Fig. 2, locality 2), 11.iv.2010, E. Líznarová and S. Korenko leg., larva on Zodarion styliferum , pupated 21.iv.2010, adult emerged 4.v.2010 (one empty cocoon and one larva that died in the laboratory were also collected from same locality). 1 ♀ and 1 ♂ Alqueva close to Moura, bank of water reservoir (38°12'N, 7°32'W, Fig. 2, locality 3), 11.iv.2010, S. Korenko leg., larvae on Zodarion styliferum , pupated 14.iv.2010, adults emerged 27.iv.2010 (female) and 28.iv.2010 (male), female escaped.

Faro district: 1 ♀ Casa do Canavial close to Mesquita in Guadiana Valley Natural Park (37°32'N, 7°31'W, Fig. 2, locality 6), 4.iv.2008, S. Korenko leg., larva on Zodarion styliferum , pupated 21.iv. 2008, emergence date not recorded. 1 ♀ and 1 ♂ Alcoutim, view terrace close to town (37°27'N, 7°28'W, Fig. 2, locality 5), 29.iii.2009, S. Korenko and S. Pekár leg., larvae on Zodarion styliferum , pupated 2.iv.2009 (female) and 1.iv.2009 (male), adults emerged 9.iv.2009.

Distribution.

South and Central Europe ( Schwarz 1998) including Portugal (new record), Azerbaijan, Tajikistan ( Schwarz 1998).

Hosts.

Juvenile spiders of Zodarion styliferum with prosoma length averaging 2.47 mm (N = 9, min/max = 1.6/3.2 mm) (new host record).

Biology

Gelis apterus and its spider hosts appear to be associated with open arid habitats with sparse vegetation. Females attack the host spiders in the igloo, penetrating the igloo wall with their long ovipositors (laboratory observation). Unfortunately nothing more is known about oviposition behaviour. The larva makes a cocoon inside the spider igloo before pupation (Figs. 6). Details about the sclerotization process of the pupa were not recorded because of its location in the cocoon. The cocoon consists of white to brownish weaved threads which fill space inside the spider igloo. Adults emerged 9-14 days after pupation.

Remarks.

Females of Gelis apterus reared from Zodarion styliferum in Portugal differ from those collected in other parts of Europe by somewhat longer ovipositor sheaths and the thorax laterally having smooth patches. In these two features they resemble the closely related species Gelis atratus (de Stefani, 1884), but females of Gelis apterus reared from Zodarion styliferum do not have the mesoscutum sloping downwards caudally.

The previously unknown macropterous males of Gelis apterus are very distinct from their apterous females. Males of Gelis are often unknown or unassociated with females because of the difference in aptery and because they are more difficult to distinguish in many species. The two sexes of Gelis apterus possess very few similar features that indicate they are conspecific and we consider the males we reared as Gelis apterus primarily because they were reared with females of Gelis apterus , and because only females of Gelis apterus were reared from Zodarion styliferum .

Diagnostic features of Gelis apterus males include an evenly and weakly convex, smooth or mainly smooth clypeus, long mandible and malar space, moderately narrowed and distinctly convex head, and the pattern of sculpture and carinae of the propodeum. These features enable separation of males from those of most other Gelis species. However, it is expected that the unknown males of Gelis atratus will be very similar to Gelis apterus and the two may not be easily distinguishable.

We found Gelis apterus associated with Zodarion styliferum in several parts of Central and South Portugal, and it seems to be widespread but in low abundance throughout the Iberian Peninsula based on the observation of three empty pupae inside Zodarion igloos in the Spanish provinces of Málaga and Granada (Korenko unpub.). Gelis is a large genus of parasitoid wasps that are worldwide in distribution but with most species in the Holarctic region. Some species are fully-winged but many are ant-like micropterous or wingless. Hosts of different species of Gelis include eggs or larvae or cocoons or cocoon-like structures of a wide range of holometabolous insects as well as egg sacs of spiders. Fitton et al. (1987) listed ten Gelis species reared from spider egg sacs of both wandering and web-building spiders. The larvae of Gelis species known to attack spiders have been regarded as exclusively feeding on spider eggs ( Fitton et al. 1987). We did not observe this for Gelis apterus , which fed on juvenile spiders. Diurnally active female Gelis apterus presumably attack nocturnal Zodarion that are resting in their igloos during the day.

Zodarion styliferum is common in Portugal and has two overlapping generations ( Pekár unpub.). Juvenile spider hosts are therefore available to Gelis apterus during the whole year and likely provide a highly available resource. Gelis apterus is documented from South - Central Europe to 70° eastern longitude. Several Zodarion species have overlapping distributions within this area. Their life history, behaviour, body size and igloo architecture are similar to Zodarion styliferum and could be potential hosts for Gelis apterus . Although we did not rear Gelis apterus from either Zodarion alacre or Zodarion atlanticum , this may simply reflect their relative rarity and low parasitism rates. Whether Gelis apterus is also associated with Zodarion species outside of the Iberian Peninsula is not known. Knowledge of the host range of Gelis apterus in other parts of its range is essential to confirm whether Zodarion spiders are their only hosts and, if not, understand how an association with spider hosts evolved.