Dibrachys lignicola Graham, 1969

Peters, Ralph S. & Baur, Hannes, 2011, A revision of the Dibrachys cavus species complex (Hymenoptera: Chalcidoidea: Pteromalidae), Zootaxa 2937, pp. 1-30 : 24-27

Dibrachys lignicola Graham, 1969

( Figs 7b, 7 e, 8b, 8e, 9b, 9e)

Dibrachys (Dibrachys) lignicola Graham, 1969: 810 , holotype female in HDOU (Type HYM: 1283) (examined by Peters). Dibrachys (Dibrachys) goettingenus Doganlar, 1987: 202 –203, holotype female in IFUG (examined by Peters); syn. n.

Diagnosis. Both sexes. Eyes large, eye height greater than 2.0x POL. Head and mesosoma with distinct metallic coloration ( Figs 7b, 7 e, 8b, 9b).

Female. Gaster short and eyes broad, gaster length equal to or less than 4.05x eye breadth ( Figs 6 , 7b , Table 7) and shorter than head plus mesosoma. Eyes broad and oval, eye height equal to or less than 1.6x eye breadth, outer margin never distinctly emarginate ( Fig. 7b ). Stigmal vein long compared to marginal vein, marginal vein mostly less than 2.0x stigmal vein (1.57–2.05, but only 2 of 47> 2.0) ( Fig. 8 e). Mesoscutum never bluish. Mouth narrow, head breadth greater than 2.0x mouth breadth ( Fig. 7 e).

Male. Scape and pedicel apically with distinct lobe on outer side ( Fig. 9 e). Gastral spot distinct ( Fig. 9b ).

Description. FEMALE ( Figs 7b, 7 e, 8b, 8e). Body length 2000–3000 μm.

Head ( Figs 7b, 7 e). Eyes large and usually oval, with outer margin rarely only very slightly emarginate; eye 1.38–1.60x as high as broad; eye height 2.11–2.68x POL. Level of lower margin of antennal toruli at level of lower ocular line. Clypeus distinctly striate vertically, though less distinct towards lower margin. Lower face only moderately receding. Mouth narrow, head breadth 2.10–2.55x mouth breadth; mouth breadth 2.38–2.92x malar space. POL 1.55–2.11x OOL. First anellus ringlike, second anellus slightly longer than broad; first funicular segment slightly longer than broad, second to fifth quadrate, and sixth slightly transverse; flagellum 0.63–0.77x head breadth.

Mesosoma ( Fig. 8b ). Mesoscutum and scutellum slightly convex in lateral view. Mesoscutum 0.51–0.61x as long as broad. Reticulation coarse, slightly coarser than in D. microgastri , 10.7–14.9 meshes/200 μm in anterior part of mesoscutum. Marginal rim of scutellum only moderately turned upwards. Plicae straight or weakly curved; median carina weak or interrupted.

Wings ( Fig. 8 e). Wings hyaline; stigmal vein long, marginal vein only 1.57–2.05x stigmal vein; submarginal vein 1.74–2.24x marginal vein.

Metasoma ( Fig. 7b ). Gaster shorter than head plus mesosoma; massive and broad, moderately pointed; length 3.54–4.05x eye breadth. Tergites smooth, weakly alutaceous and with some strong hairs in apical half of gaster.

Color ( Figs 7b, 7 e, 8b). Head with distinct metallic coloration, usually dark green. Antenna varying from brown to dark brown, in general slightly darker than in D. microgastri . Mesosoma with distinct metallic coloration, but never blue or almost black, mostly with distinct tinge of bronze or gold, especially on scutellum; ventral surface black with tinge of blue. Venation of wings light brown. Coxae concolorous with mesosoma. Trochanters, femora and tibiae usually yellow or light brown, rarely brown, generally lighter than in D. microgastri . Tarsi yellow, last two segments of metatarsus sometimes darker. Gaster brown to dark brown, shiny.

MALE ( Figs 9b, 9 e). Similar to female except as follows. Smaller, body length 1500–2000 μm.

Head. Eye height 2.19–2.62x POL. Scape and pedicel apically with distinct lobe on outer side ( Fig. 9 e).

Color ( Fig. 9b ). Mesoscutum and scutellum always distinctly metallic green or dark green, rarely with a slight tinge of blue; bronze on scutellum mostly indistinct. Coxae dark brown, sometimes at least in part concolorous with mesosoma. Gaster with distinct light testaceous spot on ventral side of anterior segments, the spot also visible in dorsal view.

Material examined. England: Berkshire, Slough, reared from Crataerina pallida pupae by Woodroffe 1951 (A, 5 females) ( BMNH) (det. Dibrachys sp.); Farnham, reared from Diptera puparium (A, 2 females) ( BMNH) (det. D. cavus ); Hampshire (Hants), reared from dead Larix trunk (A, 5 females, 2 males) ( BMNH) (det. D. boarmiae ). France: Sollies Pont, reared from pupae of Cydia pomonella (A, 2 females, 1 male) ( BMNH) (det. D. cavus ). Germany: Hamburg, reared from puparia of Triarthria setipennis , leg. R. Peters March 2006 (6 of numerous females A, and numerous males) ( ZMH); Hamburg, stock HRL, laboratory rearing on Calliphora vomitoria (20 of numerous females A, and numerous males) ( ZMH); Hamburg, reared from Ocytata pallipes , leg. R. Peters (numerous females and males) ( ZMH); Hamburg, stock HRL II (numerous females and males, including specimens in Figs 7–9 ); Hessen: Bad Arolsen, host Ornithomya avicularia , leg. K. Staiber March 2005 (2 females, 1 male, all dead inside host puparium) ( ZMH); Göttingen, reared from Gilpinia hercyniae , holotype of Dibrachys goettingenus (A, 1 female) ( IFUG); paratypes of D. goettingenus , same data as holotype (all 3 females A, 1 male) ( IFUG); paratypes of D. goettingenus , same data as holotype (A, 2 females) ( BMNH). Ireland: Dublin, Harold's Cross, 22.viii.1954, on a wooden post in garden at 14, Clareville Road, holotype of Dibrachys lignicola (1 female A) ( HDOU); paratypes of Dibrachys lignicola , same data as holotype (all 5 females A, 1 male) ( BMNH); Dublin, Harold’s Cross, paratype of D. lignicola , in house (A, 1 female) ( BMNH). Italy: Tuscany, reared from Phryxe caudata on Thaumetopoea pityocampa (A, 8 females, 1 male) ( BMNH) (det. Dibrachys sp.); Conca del Re Castrovillari, NP of Pollino, reared from Phryxe caudata associated with Thaumetopoea pityocampa (1 female) ( ZMH). Morocco: Mamora, reared from Apanteles sp. on Lymantria dispar (2 females, 1 male) ( BMNH) (det. D. cavus ). Switzerland: Vaud Bonvillars, ex bird nest (A, 2 females) ( NMBE) (det. D. cf. goettingenus ). USA: California, Riverside, reared from tachinid puparium (A, 6 females, 5 males) ( BMNH) (det. D. cavus ). (Former) Yugoslavia: no host (1 female) ( BMNH) (det. D. cavus ).

Biology. Noyes (2003) listed only a single lepidopteran host record for D. lignicola , though also one hymenopteran species for D. goettingenus based on Doganlar (1987). Our study shows D. lignicola uses pupae of Diptera ( Tachinidae , Hippoboscidae ) in addition to Hymenoptera ( Diprionidae , Braconidae ) and Lepidoptera (Tortricidae) ( Table 11 ). We added to the records in Noyes (2003) several other countries that are in the range of distribution of D. lignicola ( Table 11 ). The record from North America ( USA) is a single record and needs confirmation. There are only two records from Africa ( Algeria ( Noyes 2003), Morocco). The Moroccan record from Apanteles sp. cocoons is extraordinary because it is the only record from parasitic Hymenoptera , though we frequently found this species in the puparia of two earwig parasitoids ( Diptera : Tachinidae ) ( Table 11 ). The recorded host species show no obvious similarities, but the revised taxonomy and key to species might help to identify further aspects of this species’ biology in the future.

Distribution. See Table 11 for confirmed records.

Taxonomic remarks. The establishment of D. goettingenus by Doganlar (1987) was most probably made only because the description of D. lignicola by Graham (1969) is incomplete. Graham only mentioned the lobe on the scape in males and makes no statement about a lobe on the pedicel. Doganlar used the lobe on both the scape and pedicel as the main diagnostic character for his D. goettingenus . Doganlar was unable to check the character for D. lignicola males because Graham’s collection was not accessible to him. It is now part of the NHM collection and we examined the type series of D. lignicola , which showed that male paratypes have a distinct lobe on both the scape and pedicel. Further differences mentioned by Doganlar (1987: 203) to distinguish the two species proved unreliable. The ratio of eye height to eye breadth in females varies more strongly than indicated by Doganlar and also the difference in the POL to OOL ratio was not confirmed.

Though males of Dibrachys lignicola and D. microgastri are easily distinguished by the structure of the scape and pedicel, females are difficult to differentiate. The diagnostic characters used by Graham (1969) and Doganlar (1987) to separate the females of the two groups, the ratios of eye height to breadth, mouth breadth to malar space, and gaster length to length of head plus mesosoma, proved to overlap in our morphometric analysis. The separation of D. lignicola and D. microgastri females is only possible using the characters given in our key (see also Fig. 6 and Table 7), though there is still no single character known to completely separate females of the two species. If the identification is in doubt one should simply try another specimen of these gregarious parasitoids, if accessible.

country host species

Diagnosis. Both sexes. Eyes small, eye height equal or less than 2.0x POL ( Figs 7c , 9c ). Head and mesosoma black without metallic coloration or only with slight tinge of bronze, brown or green ( Figs 7c, 7 f, 8c, 9c, 9f).

Female. Gaster shorter than head plus mesosoma ( Fig. 7c ). Eyes oval, eye height less than 1.6x eye breadth, outer margin never distinctly emarginate ( Fig. 7c ). Mouth broad, head breadth equal to or less than 2.0x mouth breadth ( Fig. 7 f).

Male. Scape and pedicel apically without lobe on outer side ( Fig. 9 f). Gastral spot distinct ( Fig. 9c ).

Description. FEMALE ( Figs 7c [holotype], 7f, 8c, 8f [paratype no. 15]). Body length 1780–2650 μm.

Head ( Figs 7c, 7 f). Eyes small and oval, outer margin not emarginate; eye 1.32–1.57x as high as broad; eye height 1.69–2.00x POL. Level of lower margin of antennal toruli at level of lower ocular line. Clypeus striate vertically, indistinctly reticulate in its median part. Lower face distinctly receding. Mouth broad, head breadth 1.75– 2.00x mouth breadth; mouth breadth 2.47–3.04x malar space. POL 1.71–2.20x OOL. First anellus small and ringlike, second anellus distinctly transverse rectangular, 1.5x broader than long; first funicular segment longer than broad, second to sixth almost quadrate; flagellum 0.68–0.77x head breadth.

Mesosoma ( Fig. 8c ). Mesoscutum flat, scutellum slightly convex in lateral view. Mesoscutum 0.51–0.60x as long as broad. Reticulation of pronotal collar, mesoscutum, scutellum and frenum fine, 13.1–17.0 meshes/200 μm in anterior part of mesoscutum. Marginal rim of scutellum distinctly turned upwards. Plicae distinct, weakly curved; median carina distinct or interrupted.

Wings ( Fig. 8 f). Wings hyaline; marginal vein 1.43–2.07x stigmal vein; submarginal vein 2.06–2.37x marginal vein.

Metasoma ( Fig. 7c ). Gaster shorter than head plus mesosoma; broad, oval and not distinctly pointed; length 3.50–4.61x eye breadth. Tergites not very smooth and not very shiny, weakly alutaceous, especially in apical half of gaster and with few, but distinct and strong hairs; sternites without hairs.

Color ( Figs 7c, 7 f, 8c, 8f). Head and mesosoma black, without metallic coloration, sometimes with slight tinge of brown or bronze on face, vertex, mesoscutum, scutellum and axillae. Antennal segments varying from light brown to brown, flagellum usually slightly darker than scape and pedicel. Venation of wings usually pale brownish.

Legs light brown, metafemur brown; coxae brown, proximal parts sometimes concolorous with mesosoma. Gaster dark brown.

MALE ( Figs 9c, 9 f [paratype no. 11A]). Similar to female except as follows. Smaller, body length 1340–2050 μm.

Head. Eye height 1.55–1.92x POL. Level of lower margin of antennal toruli slightly above lower ocular line. Scape and pedicel apically without lobe on outer side.

Metasoma ( Fig. 9c ). Gaster almost circular.

Color ( Figs 9c, 9 f). Head black or sometimes with tinge of bronze and green a little more distinct than in females. Antennae usually completely light brown. Gaster with distinct light testaceous spot on ventral side of anterior segments, the spot also visible in dorsal view.

Material examined. Holotype female. Germany: Schwarzwald, Eschbach, reared from Dolichovespula saxonica , labeled leg. R. Gauss, leg. 3.ii. 1966, ex Dolichovespula saxonica det. R. Gauss, Dibrachys sp. [prope vesparum (Ratz.) ] Zd. Bouček 1968; det. R. Peters 2009. Deposited at SMNS.

Paratypes. Austria: S.E. Styria, coll. 30.v.82 CIBC, ex Sphecophaga vesparum in V. saxonica , labeled Dibrachys (?) vesparum (Ratz.) det. Z. Bouček, 1984 (7 females (NHM no. 1–7)) ( BHNH). England: London, no host, labeled Syn. Pteromalus vitripennis , det. Bouček 1977, paralectotype of D. boarmiae (1 female) ( BMNH) (det. D. boarmiae , transferred to D. verovesparum ). Germany: all specimens from Schwarzwald, Eschbach; coll. 2.ii.1966, ex Dolichovespula saxonica (P.) det. R. Gauss, labeled M.W.R. de V. Graham coll. BMNH (E) 1995-489 (1 female (NHM no. 8), 1 male) ( BMNH); leg. 4.ii.1966, ex Dolichovespula saxonica det. R. Gauss, Dibrachys sp. [prope vesparum (Ratz.) ] Zd. Bouček 1968 (1 female) ( SMNS); leg. 7.ii.1966, ex Sphecophaga vesparum Curt. det. R. Gauss, Dibrachys vesparum (Ratz.) det. R. Gauss (3 females, 3 males, including paratype no. 11A) ( SMNS); leg. 7.ii.1966, ex Sphecophaga vesparum Curt. det. R. Gauss, Dibrachys spec. nahe vesparum (Rtzb.) det. Z. Bouček (8 females, 2 males, including paratype no. 15) ( SMNS); leg. 21.ii.1966, ex Sphecophaga vesparum Curt. det. R. Gauss, Dibrachys sp. [prop. vesparum (Ratz.) ] Zd. Bouček 1968 (3 females, 3 males [1 female, 1 male in SMNS; 1 female, 1 male in NMBE; 1 female, 1 male in ZMH]); ex Sphecophaga vesparum Curt. det. R. Gauss, Dibrachys vesparum (Ratz.) det. R. Gauss (4 females, 4 males) ( SMNS); ex Sphecophaga vesparum Curt. det. R. Gauss, Dibrachys vesparum (Ratz.) det. Z. Bouček (1 female [paratype 12, not used for morphometric analysis], 1 male) ( SMNS).

Biology. The host species of D. verovesparum are Dolichovespula saxonica ( Hymenoptera : Vespidae ) and Sphecophaga vesparum (Curtis) ( Hymenoptera : Ichneumonidae ), a primary parasitoid of Vespidae . Further collection of vespid nests is necessary to increase our knowledge on life history of this species.

Distribution. Europe. Germany, Black Forest; Austria, Styria; England.

Etymology. From the Latin verus, meaning “true”, and vesparum ; referring to the material in Graham (1969: 810) that he considered might be the “true” D. vesparum , which we interpret as a new species (see under “Taxonomic remarks” for D. microgastri ).

Taxonomic remarks. Our interpretation of the name D. vesparum , which was described originally from females reared from a wasp nest, is discussed under D. microgastri . Based on the original description we do not think D. vesparum is conspecific with our new species.

Figures

FIGURE 6. Scatterplot of the two best ratios for separating group cavus (circles) from group lignicola (triangles) (see also Table 7). Specimens with missing values not included.

FIGURE 7. a – c, habitus (lateral) of female: (a) Dibrachys microgastri (Bouché); (b) D. lignicola Graham; (c) D. verovesparum Peters & Baur, holotype. d – f, head (frontal) of female: (d) D. microgastri; (e) D. lignicola; (f) D. verovesparum. Scale bars a – c = 500 μm; d – f = 100 μm.

FIGURE 8. a – c, mesosoma (dorsal) of female: (a) Dibrachys microgastri (Bouché); (b) D. lignicola Graham; (c) D. verovesparum Peters & Baur. d – f, forewing of female: (d) D. microgastri; (e) D. lignicola; (f) D. verovesparum. Scale bars a – c = 250 μm; d – f = 500 μm.

FIGURE 9. a – c, habitus (lateral) of male: (a) Dibrachys microgastri (Bouché); (b) D. lignicola Graham; (c) D. verovesparum Peters & Baur. d and e, antenna (dorsal) of male: (d) D. microgastri; (e) D. lignicola. f, head with antenna (dorsal) of male; D. verovesparum. Scale bars a – c = 500 μm; d – f = 250 μm.

Tables

TABLE 11. Hosts and geographic distribution of Dibrachys lignicola.

Germany	Triarthria setipennis Ocytata pallipes Ornithomya avicularia Gilpinia hercyniae	Diptera : Tachinidae Diptera : Tachinidae Diptera : Hippoboscidae Hymenoptera : Diprionidae
France	Cydia pomonella	Lepidoptera : Tortricidae
Italy	Phryxe caudata	Diptera : Tachinidae
Switzerland
former Yugoslavia
England	Crataerina pallida	Diptera : Hippoboscidae
Ireland
Morocco	Apanteles sp.	Hymenoptera : Braconidae
USA (California)	Tachinidae sp.	Diptera : Tachinidae
Dibrachys verovesparum (Figs 7c, 7f, 8c, 8f, 9c, 9f)	Peters & Baur sp. n.