Arastichus Gates, Hanson, Jansen-Gonzalez & Zhang, 2022

Zhang, Y. Miles, Gates, Michael W., Hanson, Paul E. & Jansen-Gonzalez, Sergio, 2022, Description of a Neotropical gall inducer on Araceae: Arastichus, gen. nov. (Hymenoptera, Eulophidae) and two new species, Journal of Hymenoptera Research 92, pp. 145-172 : 145

Arastichus Gates, Hanson, Jansen-Gonzalez & Zhang gen. nov.

Figs 3 , 4-5 , 6-7 , 8-9 , 10-15 , 16-20 , 21-25

Type species.

Arastichus gallicola ( Ferrière).

Diagnosis.

Vertex with single erect seta mesad to eye margin, ~0.5 × eye height (Fig. 10 ); vertex depressed posteriad and laterad lateral ocelli (Figs 12 , 22 ); toruli positioned above middle of face, 1-1.5 × torular diameters from median ocellus (Figs 10 , 21 , 24 ); intrascrobal carina step like in lateral view with V-like carinae diverging to lateral margins of median ocellus (Figs 12 , 22 ); antennal formula 11242 (Fig. 14 ) or 11342 in A. capiculata . A1 ~1.5 × wider at apex rather than base (note: often appears subdivided, representing fusion of two segments) wedge-like in lateral view, longest ventrally; ventral plaque present in male scape (Figs 5 , 7 , 9 ); clypeus bilobed, lobes apically truncate; gena ventrally extended beyond oral fossa/base of mandible (Figs 10 , 21 , 24 ); mesosoma shiny dorsally (Fig. 23 ); scutellum lacking submedian grooves (Figs 16 , 23 ); petiole membranous ventrally; a tuft or sometimes one seta(e) anterad mesocoxa (Fig. 9 ); propodeal spiracles large, ~0.3 × length propodeum; distinct, suberect setation on mesal surface of procoxa and metacoxa (Figs 8 , 9 ), Gt6 with spiracular rim elevated (Fig. 19 ).

Arastichus gallicola was first described by Ferrière (1924) as Trichaporus gallicola , which was then transferred to Exurus Philippi by Costa Lima (1959a). LaSalle (1994) synonymized Exurus with Aprostocetus , through its type species E. colliguayae Philippi. He was hesitant about the status of A. gallicola (Fig. 3 ) as he was not able to examine any type specimens, but commented that it is quite distinct and warranted its own genus. As Ferrière did not designate a holotype, we hereby designate the top left specimen (female) on the pin with three other specimens as the lectotype (Fig. 3 ). The degree of morphological variation seen in Aprostocetus makes it difficult to characterize consistently using few characters; however, according to LaSalle (1994), most species have the SMV with ≥ 3 seta, propodeal spiracle partially covered by overhanging lobe of callus, and one cercal setae distinctly longest and sinuate or curved. Although Arastichus shares these diagnostics, several additional apomorphies set it apart from Aprostocetus (as noted in the diagnosis above).

Description.

Coloration: Female. Length 3.8-5.2 mm. Head, antennae, body, coxae, and legs yellow or brown (Figs 3 - 9 ). Tegula pale golden. Pronotum either completely brown, or yellow except for the anterolateral panel. Ventral mouthparts and tarsomeres pale yellow. Female fore wing with soft opaque area at basal and cubital folds, disc hyaline (Fig. 4 ). Male fore wing with opaque base of cubital and basal folds; disc with soft opaque pattern (Fig. 5 ).

Head: Surface rugulose or umbilicately punctate dorsally, laterally, and anteriorly, 1.3-1.6 × as broad as high. Supraclypeal area concave, glabrous, asetose (Figs 10 , 21 , 24 ), extending to toruli; lower tentorial pits minute. Genal carina present, extending to lower third of eye posteriorly (Figs 10 , 13 ). Torulus with dorsal margin positioned at lower ocular line; intertorular space punctate, obtusely pointed; scrobal depression margined laterally, margin fading dorsally, reticulate with fine irregular rugae and with median carina between depressions in ventral half (Fig. 10 ). Eyes setose, seta sparsely distributed and very short. Mandible tridentate with apical and middle teeth acute, basal tooth broad and rounded (Fig. 21 ). Clypeus emarginate in step-like manner (Fig. 21 ), medially produced. Posterior surface of head without postgenal lamina, postgenal grooves slightly ridged, slightly convergent ventrally, extending to upper margin of hypostomal bridge; dorsal margin of lateral foraminal plate obliterated; subforaminal plate absent; postgenal sulci distinct; postgenal bridge glabrous (Fig. 11 ). Antenna (Figs 14 , 15 ) with scape broadest medially, coarsely imbricate. Pedicel triangular in lateral view, narrowed ventrally; anelli (two in all species except A. capipunctata , which has three) transverse, glabrous; F1 chalice-shaped, imbricate in basal half (Fig. 14 ); funicle with each segment fusiform, longer than broad, apically truncate with two rows of MPS and sparse, semi-erect setation; F5-6 fused, apex with radially asymmetric sensillar area (Fig. 14 ).

Mesosoma: Surface smooth, rugulose or umbilicate with interstices alveolate. Pronotum in dorsal view 2.2-3.3 × as broad as long. Mesoscutal midlobe 1.0-1.1 × as broad as long; notaulus complete, clearly indicated (Fig. 16 ). Scutellum 1.2-1.3 × as long as broad at its widest; broadly convex dorsally. Scutellum distinctly overhanging dorsellum. Sublateral prepectal concavity shallow; epicnemium flattened, with superficial submedial, shallow depressions to receive procoxa, these separated by low carina connecting to epicnemial carina ventrally. Procoxa imbricate anterobasally and medially, flat, low diagonal carina separating this area from umbilicately punctate anteroventral and lateral portion of procoxa; mesocoxa rugulose to imbricate; mesocoxal foramina narrowly open posteriorly; metacoxa rugulose to imbricate. Metapleuron and lateral areas of propodeum shallowly umbilicate, propodeum vaguely rounded laterally (Fig. 20 ), bordered laterally by reticulate sculpture overlain with umbilicate punctation; spiracle situated about 1/3 its greatest diameter from dorsellum, median channel with series of distinct transverse carinae (Fig. 20 ). Fore wing hyaline, venation whitish, setae pale brown, evenly distributed; PMV 1.0-1.1 × of V and S 0.7-0.8 × of M. Basal cell delimited by cubital and basal folds; speculum present; disc uniformly setose; number of dorsal setae on submarginal vein: female: 2-3, male: 1-4. Parastigma not swollen; marginal vein constricted near its base after parastigma and three times as long as stigmal vein. Stigmal vein at an angle of 20°-30° in relation to marginal vein. Uncus small, not extending far from stigma. Postmarginal vein reduced, less than 1/4 of stigmal vein (Figs 4 , 5 ). Hind wing disc evenly setose. with apex of vein (at hamuli) not swollen or knobbed but darkened, with three hamuli.

Metasoma: Petiole 0.3-0.4 × as long as broad in dorsal view, laterally protuberant, connected by dorsal transverse carina. Gaster ovate in lateral view; all terga with finely imbricate sculpture, evenly setose, setae fine and erect; Gt1 depressed behind petiole, setose; Gs1 fused with petiole (Fig. 19 ); syntergum short, setose; third valvula setose apically, arranged radially and curved.

Genitalia: Female: First valvifer falcate 1/4-1/8 of ovipositor total length, articulates with T9 and the second valvifer very near each other, on its proximal end; second valvifer broad, sickle-shaped; second valvula 3/4 of ovipositor length, with row of 3-4 spaced setae at apical half; third valvula 1/3-1/5 of total ovipositor length (Fig. 26 ). Male: Phallobase cylindrical, 1.5-2.0 × as long as wide, paramere pointed with one apical seta, 1/5 × the length of phallobase. Volsella 1/2-1/3 of paramere length. Digitus dorsoventrally flattened, bean-shaped in either ventral or dorsal view, 2-3 × as long as wide, bearing a single apical digital spine. Aedeagus cylindrical, dorsoventrally flattened, pointed or round at apex (Fig. 27 ).

Etymology.

Name from the host plant family, Araceae . Gender masculine.

Biology.

Ferrière (1924) first described Arastichus gallicola (as Trichoporus gallicola ) and defined the species as gall inducer on pistilate flowers of Philodendron selloum (now a synonym of Thaumatophyllum (Philodendron) bipinnatifidum ( Mayo 1991) (Fig. 3 ). Gibernau et al. (2002) described the galls of A. gallicola on flowers of T. solimoesense and reported it as a seed predator. Recently, a more detailed study of the developmental biology of A. gallicola discards seed predation and supports the idea that this species is a gall inducer specialized on ovaries of T. bipinnatifidum (SJG, unpublished).

Female wasps of A. gallicola oviposit during the period of anthesis which lasts 24-48 hours, when the inflorescence spathe is open and leaves the hundreds of pistilate flowers accessible to pollinators and female Arastichus ( Gibernau et al. 2002). Once anthesis ends the spathe closes and the space between the spathe and the inflorescence fills with a liquid, often trapping and killing the female wasps inside.

Time of development can vary from one to four months in Arastichus gallicola . Once the infrutescence attains maturity, the spathe develops an encircling dehiscent line at its base and falls, uncovering the orange fruits and galls. Exposure of galls to light and outer atmosphere might trigger adult wasp emergence from the galls, which is done by chewing through each gall wall. A single wasp develops per gall with up to six galls developing in a single fruit. It is possible to find infrutescences and/or fruits containing only seeds, combinations of seeds and galls, or only galls (Fig. 1 ).

Although we have detailed information about gall induction only in A. gallicola , it is possible that the other two species of Arastichus are also gall inducers rather than seed predators. Examination of collected material for A. gibernau and A. capipunctata indicates that the biology of these species should not be very different from that of A. gallicola .

The eurytomid Prodecatoma philodendri is associated with the galls of Arastichus gallicola and A. gibernau . Ferrière (1924) reported that Prodecatoma were phytophagous, and oviposits from the outside when the spathe is closed and Arastichus galls are in the process of formation ( Gibernau et al. 2002; SJG pers. obs.). When examining the cavities from which Prodecatoma adults emerge, a series of tunnels communicate with adjacent Arastichus galls. These attacked galls contained dismembered body parts of Arastichus pupae, indicating that Prodecatoma larvae might consume several of them along with some gall tissue ( Gibernau et al. 2002; SJG pers. obs.); this is in line with the fact that the adult Prodecatoma is about 4-5 times larger than the Arastichus adult. Thus, taken all together, P. philodendri is likely entomophytophagous, a common mode of feeding within Eurytomidae .

It is difficult to estimate the taxonomic breadth of the relationship between Arastichus and Araceae . Philodendron is traditionally subdivided in three subgenera: Meconostigma , Philodendron and Pteromischum , but members of Meconostigma have been recently recognized as a distinct genus Thaumatophyllum Schott ( Sakuragui et al. 2018). Arastichus has been found in species belonging to Thaumatophyllum ( T. bipinnatifidum , T. solimoesense ), and in the subgenus Philodendron Philodendron ( P. radiatum ). SJG has collected what seem to be female Arastichus body parts from inside closed spathes of P. cordatum and P. curvilobum in Brazil. Further studies and more extensive collecting are needed to determine the degree of species-specificity and to determine whether Arastichus is present in the subgenus Arastichus Pteromischum as well.

Figures

Figure 1. Illustration of the lifecycle of Arastichus gallicola with its host plant, Thaumatophyllum solimoesense (Arecaceae). Illustrated by Taina Litwak.

Figure 3. Dorsal and lateral habitus of Arastichus gallicola lectotype (female on the top left), along with three paralectotypes on the same pin.

Figure 26. Female genitalia of Arastichus spp. based on photographs of slide-mounted specimens. Morphological variations are evident among species and within species.

Figure 27. Male genitalia of Arastichus spp. based on photographs of slide-mounted specimens. Dsp digital spine; Aed aedeagus; Dqt digitus; Dsp d igital spine; Phl phallobase; Prm paramere; Vsl volsella.

Figure 4 - 5. Lateral habitus of Arastichus gallicola 4 female 5 male.

Figure 6 - 7. Lateral habitus of Arastichus capipunctata 6 holotype female 7 paratype male.

Figure 8 - 9. Lateral habitus of Arastichus gibernau 8 holotype female 9 paratype male.

Figure 10 - 15. Arastichus gallicola 10 frontal view of head 11 posterior view of head 12 dorsal view of head 13 anterolateral view of head 14 female antenna 15 male antenna.

Figure 16 - 20. Arastichus gallicola 16 dorsal view of mesosoma 17 ventral view of mesosoma 18 ventral view of female metasoma 19 lateral view of female metasoma 20 propodeum.

Figure 21 - 25. Arastichus capipunctata 21 frontal view of head 22 dorsal view of head 23 dorsal view of mesosoma, arrow pointing to the bilobed posterior margin of mesoscutum 24 - 25 Arastichus gibernau 24 frontal view of head 25 lateral view of mesosoma, arrow pointing to the circular fossa on the posterior corner of metapleuron.