Acorystus Townes

Scherrer, Marcus V., Santos, Bernardo F. & Aguiar, Alexandre P., 2010, Generic redefinition, key and two new species of Acorystus To w ne s (Hymenoptera: Ichneumonidae: Cryptinae), Zootaxa 2721, pp. 28-38 : 29-30

Acorystus Townes

Acorystus Townes, 1970: 225 –226, 455. Description, figure. Type species: Acorystus fulvus Townes , by monotypy and original designation.

Redescription. Fore wing 5.1–7.6 mm. Body entirely shiny, sparsely punctate. Head: clypeus small, in front view somewhat triangular, base much narrower than apex, strongly convex; apical margin convex, without median tooth; mandible small, slightly to moderately tapered toward apex, ventral tooth about 0.4–0.5 as long as dorsal tooth; supra-antennal area with median conical horn slightly below its center; female flagellum regular, not flattened or enlarged subapically, with white band covering 4–15 flagellomeres; temple and gena very narrow, giving head triangular aspect in frontal view; gena about 0.9 as long as basal width of mandible; profile of temple at dorsal 0.3 about 0.1–0.2 as long as eye; occipital carina high, sharp near mandible, meeting hypostomal carina near mandible base.

Mesosoma : dorsal margin of pronotum weakly to moderately swollen; pronotal collar bordered by distinct carina; epomia absent; mesoscutum subcircular; notaulus reaching beyond middle of mesoscutum, slightly to strongly impressed, convergent, smooth; scuto-scutellar groove smooth; epicnemial carina restricted to ventral 0.5– 0.8 of mesopleuron; sternaulus incomplete, stronger at anterior half, posterior 0.3–0.5 very shallow to indistinct; median portion of postpectal carina short, almost indistinct, arched forwards; justacoxal carina present only as very short subvertical ridge; pleural carina absent; hind margin of metanotum with short teeth-like projections; transverse furrow at base of propodeum smooth, shallow and moderately wide. Propodeum: covered with sparse to moderately dense long hairs; anterior margin centrally concave; spiracle elliptical, SWL 2.00–2.33; anterior transverse carina strong, almost straight or slightly arched forwards; posterior transverse carina and longitudinal carinae completely lacking. Legs: fore tibia of female regular, not swollen; all pre-apical tarsomeres weakly to moderately bilobed; FLW 5.21–5.94. Wings: bulla at fore wing vein 1M+Rs large, placed at basal 0.25; ramellus absent; crossvein 1cu-a ending opposite or shortly basad to base of vein 1M+Rs; crossvein 2-Cu about 0.43–0.54 as long as crossvein 2cu-a, veins distinctly angled; cell 1+2Rs (areolet) small, APH 0.30–0.37, transversely elongate, AWH 1.86–2.67; crossvein 3r-m spectral, longer than 2r-m; vein 3-M tubular, as long as 2-M or shorter; hind wing vein M+Cu subapically strongly convex; HW1C 1.10–1.27; crossvein 1r-m with bulla at ventral 0.3; veins 1Rsa and 1Rsb weakly angled or almost continuous; veins Cub and 2-1A not reaching wing margin.

Metasoma: all metasomal tergites smooth, shiny, sparsely pilose; first tergite very elongate, slender, T1LW 3.48–4.08, T1WW 1.76–1.96, without a lateral tooth or flange at base, without longitudinal carinae; spiracle at basal 0.6–0.8, not prominent; T2LW 1.54–2.16, T2WW 2.18–2.22; OST 0.84–0.89; ovipositor moderately slender, straight, smooth, apically strongly compressed, moderately pointed; dorsal valve without or with very weak nodus and notch, ventral valve with very weak apical teeth restricted to tip.

Comments. Acorystus can be readily differentiated from other Neotropical Mesostenina by lacking entirely the posterior transverse carina of propodeum. In all other genera of the subtribe, the posterior carina is at least partially developed ( Harpura Townes , Mecistum Townes , Mesostenus Gravenhorst ) or represented by distinct crests or spine-like apophyses ( Cryptanura Brullé , Bicristella Strand , Hercana Townes , Polycyrtus Spinola – see Townes 1970). According to the present generic redefinition, it can be additionally diagnosed by the following combination of characters: body surface entirely shiny and mostly impunctate ( Figs 1–3 ); mandible short and slender; supra-antennal area with a single conical horn ( Figs 4, 8 ); epomia absent ( Fig. 1 ); first tergite without lateral tooth at base ( Figs 2, 3 ); and ovipositor tip very slender, without nodus, ventral valve apex with very weak teeth ( Figs 7, 11 ). Both of the new species fit well in the key for the mesostenine genera provided by Townes (1970), except by the propodeal punctures, very weak and widely spaced in the new taxa, contrasting with the “coarse punctures” observed in A. fulvus . In that case, the absence of a pair of apophyses mentioned in the key, as well as the illustrations provided, suffice to clearly differentiate all females of Acorystus and Polycyrtus . Some males of Polycyrtus , however, have weak or almost indistinct propodeal apophyses; in this case, the correct determination of Acorystus must consider the generic redefinition provided above.

Considering the large number of Cryptinae specimens examined, it seems remarkable that so few specimens of the genus were found. That might indicate that Acorystus is a very rare taxon, even though it is clearly widespread; the known records for each of its species – Peru, Amazon Basin and Atlantic Forest – are between 2,281–3,379 km far apart from each other. The rarity of specimens, however, may also be due not only to rarity itself, but at least in part also to implicit limitations of the sampling methods. This is suggested from the fact that all specimens discussed in the present work were collected with Möricke traps (yellow pans), even though these were used concurrently with many Malaise traps, in all of the respective collecting trips. While perhaps a surprising fact, it has already been shown that, at least for Neotropical Cryptini , sampling with Möricke and Malaise traps yields very different genus-level assemblages, with about half of the genera being captured mostly or almost exclusively by Möricke traps ( Aguiar & Santos 2010). Better sampling with Möricke traps seems therefore likely to reveal further species of Acorystus in South America. Even so, Acorystus still hardly seems to be a common or speciose group.

Biology. Unknown.

Distribution. Recorded from only four localities, representing a wide geographic spam, but all of them corresponding to humid rain forests.

Figures

FIGURE 1. Acorystus circumflexus sp. nov., holotype Ψ, habitus. Photographed by Berthil B. Longo.

FIGURES 2, 3. 2, Acorystus circumflexus sp. nov., holotype Ψ, dorsal. 3, A. albicornis sp. nov., holotype Ψ, dorsal. Illustrations not to scale. Photographed by Berthil B. Longo.

FIGURES 4 – 11. 4 – 7, Acorystus albicornis sp. nov. 4, Holotype Ψ, head, dorsal; ob, orbital band. 5, Paratype Ψ, head, frontal. 6, Holotype Ψ, metapleuron, propodeum and first metasomal tergite, lateral. 7, Holotype Ψ, ovipositor tip, lateral. 8 – 11, A. circumflexus sp. nov., holotype Ψ. 8, Head, dorsal. 9, Head, frontal. 10, Metapleuron, propodeum and first metasomal tergite, lateral. 11, Ovipositor tip, lateral. Illustrations not to scale. All illustrations, except 5 and 9, photographed by Berthil B. Longo.