Conostigmus dimidiatus ( Thomson, 1858 )

Trietsch, Carolyn, Mikó, István, Ezray, Briana & Deans, Andrew R., 2020, A Taxonomic Revision of Nearctic Conostigmus (Hymenoptera: Ceraphronoidea: Megaspilidae), Zootaxa 4792 (1), pp. 1-155 : 37-42

Conostigmus dimidiatus ( Thomson, 1858)

Figs. 21 , 22 , 23

Species Comments and History. Thomson (1858) described the genus Dichogmus , unique for its incomplete (or absent) median mesoscutal sulcus, and described D. dimidiatus as the only species in the genus. Thomson (1858) described the species from a holotype female specimen, but he also described the male antennae in the original description, indicating that he did have a male specimen as well as the female. The female type is present at the MZLU and is in good condition, but the location of the male specimen is unknown.

Dessart (1973) later synonymized the genus Dichogmus with Conostigmus and redescribed C. dimidiatus , reporting more specimens collected across Europe. Dessart (1973) designated a female lectotype and male allotype, providing illustrations of a dorsal habitus view of the female, as well as detailed illustrations of the male genitalia, male and female antennae and the pterostigma of the reduced wings.

Concerning the natural history of this species, Thomson (1858) described the species from specimens found in dry sand pits near Lund, Sweden. Dessart (1973) also reported having found a male specimen on a sandy path and notes that the female type specimen of the synonymous species Dichogmus formicarius Kieffer, 1917 was found with the ant species Lasius flavus Fabricius, 1781 . Dessart (1973) reported an additional female specimen from Switzerland found with the ant species Lasius fuliginosus Latreille, 1798 .

Although Dichogmus was only known from Palearctic specimens, Dessart (1973) noted that the genus was included in keys for Europe, the Americas and Australia. Ashmead (1893) also reported Dichogmus as “a European genus not yet recognized in America” (pg. 119). However, no specimens were known from the Nearctic until now. Here, we report the first Nearctic specimens from Arizona, California, and Colorado, USA, and British Columbia, Canada, expanding the species range from Palearctic to Holarctic.

Variability. The median mesoscutal sulcus is absent in some specimens ( PSUC _FEM 34209, INHS Insect Collection 14038) and present in others ( PSUC _FEM 50307, UCRC _ ENT 00103617 , MZLU Type No. 5329: 1). However, when it is present, it is never adjacent to the transscutal articulation, and always ends anterior to the transscutal articulation. The preoccipital furrow is present in some specimens ( INHS Insect Collection 14038, MZLU Type No. 5329: 1) and absent in others ( UCRC _ ENT 00103617 , PSUC _FEM 50307). However, the preoccipital furrow always ends posterior to the ocellar triangle .

There are also slight differences in coloration between specimens. The petiole neck and anterior region of the syntergite can be lighter in coloration than the posterior region of the syntergite on some specimens (INHS Insect Collection 14038) but not on others (UCRC_ENT 00457080).

Differences between Nearctic and Palearctic Populations. The only Palearctic specimen we observed was the lectotype from Lund, but we did not observe any remarkable differences between this specimen and Nearctic specimens.

Differences Between Males and Females. Other than genitalia differences and sexual dimorphism in the antennae, there are no obvious differences between males and females.

Diagnosis. This species is recognizable by the following combination of characters: head width in dorsal view at least 1.3× wider than the mesosoma, wings absent or brachypterous, pronotum not enlarged (pronotum shorter than mesoscutum along the midline), and median mesoscutal sulcus absent or terminating anterior to the transscutal articulation in males and females. The species also has unique coloration, with the anterior half of the mesosoma (yellow to light brown in color) lighter than the posterior half of the mesosoma (light brown to brown in color).

One similar species is C. muesebecki , which shares the absence of the median mesonotal furrow and absent or reduced wings. This species can also have similar coloration. However, the two species differ in that the pronotum is enlarged (pronotum longer than mesoscutum along the midline) in C. muesebecki and not in C. dimidiatus (pronotum shorter than the mesoscutum along the midline). Another similar species is C. erythrothorax , which also has absent or reduced wings and can have similar coloration. However, C. erythrothorax also has the median mesoscutal sulcus present and complete (median mesoscutal sulcus posterior end adjacent to the transscutal articulation), whereas C. dimidiatus does not.

Description. Note: Measurements are given for the two female specimens in the following order: UCRC_ENT 00103617, INHS Insect Collection 14038.

Body length: 1.175 –1.775 mm. Color hue pattern in male: cranium, metasoma, flagellomeres brown to black; anterior half of mesosoma yellow to light brown; posterior half of mesosoma light brown to brown; legs, scape, pedicel ochre to light brown. Color intensity pattern in male: cranium darker than mesosoma, flagellomeres darker than legs; flagellomeres darker than scape and pedicel; mandible lighter than cranium; anterior half of mesosoma lighter than posterior half of mesosoma. Color hue pattern female: same as males; cranium, metasoma, flagellomeres brown to black; anterior half of mesosoma yellow to light brown; posterior half of mesosoma light brown to brown; legs, scape, pedicel ochre to light brown. Color intensity pattern female: legs lighter than the flagellomeres, scape and pedicel; cranium darker than mesosoma; distal portion of pedicel lighter than rest of pedicel; basal portion of scape lighter than rest of scape; anterior half of mesosoma lighter than posterior half of mesosoma. Color intensity dorsal and ventral to the site of the sternaulus: concolorous. Color intensity pattern of syntergite: petiole neck and anterior region of syntergite concolorus with the posterior region of the syntergite; petiole neck and anterior region of syntergite lighter in coloration than the posterior region of the syntergite. Foveolate sculpture on body count: absent. Rugose sculpturing count: absent. Rugose region on upper face count: absent.

Antennae: Male scape length vs. pedicel length: 3.1–4.0. Male scape length vs. F1 length: 1.2–1.6. Male F1 length vs. pedicel length: 2.5–3.0. Male F1 length vs. male F2 length: 1.0–1.4. Longest male flagellomere: F1. Female scape length vs. pedicel length: 3.29, 3.6. Female scape length vs. F1 length: 3.29, 3.27. Female F1 length vs. F2 length: 1.17, 1.10. Female F1 length vs. pedicel length: 1.0, 1.1. Longest female flagellomere: F9. Length of setae on male flagellomere vs. male flagellomere width: setae shorter than width of flagellomeres. Sensillar patch of the male flagellomere pattern: F7–F9.

Head: Head width, dorsal view: at least 1.3× wider than mesosoma. Head height (HH, lateral view) vs. eye height (EHf, anterior view): HH:EHf=1.2–1.5. Head height (HH) vs. head length (HL): HH:HL=1.2–1.4. Head width (HW) vs. interorbital space (IOS): HW:IOS=1.7–2.3. Head width (HW) vs. head height (HH): HW:HH=1.1– 1.3. Cephalic size (csb): Mean: 285–445 μm. Maximum eye diameter vs. minimum eye diameter: 1.1–1.4. POL: OOL: POL equal to or shorter than OOL and ocellar triangle with short base; POL longer than OOL and ocellar triangle with wide base. Male ocular ocellar line (OOL) vs. lateral ocellar line (LOL): OOL:LOL=1.6–1.8. Male ocular ocellar line (OOL) vs. posterior ocellar line (POL): OOL:POL=1.1–1.2. Male ocular ocellar line (OOL): posterior ocellar line (POL): lateral ocellar line (LOL): 1.6–1.8:1.4–1.5:1.0. Female ocular ocellar line (OOL) vs. lateral ocellar line (LOL): OOL:LOL=1.0, 1.33. Female ocular ocellar line (OOL): posterior ocellar line (POL): lateral ocellar line (LOL): 1.33:1.33:1.0; 1.0:1.4:1.0. Head shape (anterior view): circular or triangular. Preoccipital lunula count: absent. Preoccipital carina count: absent. Occipital carina structure: occipital carina not complete. Occipital carina sculpture: crenulate. Preoccipital furrow count: absent; present. Preoccipital furrow anterior end: preoccipital furrow ends posterior to ocellar triangle. Postocellar carina count: absent. Transverse scutes on upper face count: absent. Transverse frontal carina count: absent. Randomly sized areolae around setal pits on upper face count: absent. Setal pit on vertex size: smaller than diameter of scutes. Ventromedian setiferous patch and ventrolateral setiferous patch count: absent. White, thick setae on upper face count: absent. Antennal scrobe count: absent. Facial structure count: no external corresponding structure present. Facial pit count: absent. Facial sulcus count: absent. Median facial keel count: absent. Supraclypeal depression count: present. Supraclypeal depression structure: absent medially, represented by two grooves laterally of facial pit. Intertorular area count: present. Intertorular carina count: present. Median process on intertorular carina count: present. Median process on intertorular carina shape: blunt. Median process of intertorular carina structure: process does not extend across intertorular area to dorsal margin of clypeus. Median region of intertorular area shape: convex. Ventral margin of antennal rim vs. dorsal margin of clypeus: not adjacent. Torulo–clypeal carina count: present. Subtorular carina count: absent. Mandibular tooth count: 2. Mandibular lancea count: absent.

Mesosoma: Weber length: WL=330–510 μm. Anterior mesoscutal width (AscW) vs. posterior mesoscutal width (PscW): AscW/PscW=0.7–0.9. Mesoscutal length (MscL) vs. anterior mesoscutal width (AscW): MscL/ AscW=1.5–2.0. Mesoscutal length (MscL) vs. mesoscutellar length (MscIL): MscL:MscIL= 1.1–1.3. Wing count: present; absent. Fore wing size: wings reduced or brachypterous with apex never extending past scutellum. Pronotum median length: less than longest median anatomical line of the mesoscutum. Notaulus count: present. Crenulae of notaulus width: width of the crenulae does not increase more than 2× anteriorly. Notaulus posterior end location: adjacent to transscutal articulation. Median mesoscutal sulcus count: present; absent. Median mesoscutal sulcus posterior end: not adjacent to transscutal articulation (ends anterior to transscutal articulation). Scutoscutellar sulcus vs. transscutal articulation location: adjacent. Axillular carinae count: absent. Speculum ventral limit: not extending ventrally of pleural pit line. Metapleural sulcus shape: straight. Mesometapleural sulcus count: present. Ventrolateral invagination of the pronotum count: present. Sternaulus count: absent. Epicnemial carina count: complete. Epicnemium posterior margin shape: anterior discrimenal pit present; epicnemial carina curved. Transverse striations on the ventral metapleural area count: absent. Scutes on posterior region of mesoscutum and dorsal region of mesoscutellum convexity: flat. Ventral projection of the metapleural carina count: absent. Lateral propodeal carina count: present. Lateral propodeal carina shape: inverted “U” (left and right lateral propodeal carina are adjacent to the antecostal sulcus of the first abdominal tergum submedially). Mesopostscutellum count: absent (scutellum flat). Anteromedian projection of the metanoto–propodeo–metapecto–mesopectal complex count: absent. Posterior margin of nucha in dorsal view shape: concave.

Metasoma: Transverse carina on petiole shape: straight. Paired blue iridescent ovoid patches on the syntergite count: absent. Shortest width of petiole neck vs. syntergal translucent patch maximum width: 2.0–2.2. Syntergal translucent patch maximum width vs. minimum width: 1.0–1.8. Syntergal translucent patch maximum width orientation: lateromedially. Synsternal translucent patch maximum width orientation: anterolaterally. Synsternal setiferous patch shape: linear. Synsternal setiferous patch structure: comprised of a single or double row of setae. Synsternal setiferous patch anterior end: synsternal setiferous patch begins lateral or slightly anterior to the synsternal translucent patch anterior margin. Synsternal setiferous patch posterior end: synsternal setiferous patch ends lateral or just posterior to the synsternal translucent patch posterior margin. Synsternal setiferous patch length vs. synsternal translucent patch maximum width: synsternal setiferous patch as long as the maximum width of the synsternal translucent patch. S1 length vs. shortest width: S1 wider than long.

Male Genitalia: Distal margin of male S9 shape: convex. Proximolateral corner of male S9 shape: acute. Male S9 distal setal line/setal patch count: distal setae composing transverse setiferous line or lines. Male S9 distal setal line / setal patch structure: single or double transverse row of distal setae. Distomedian hairless area interrupting transverse row of setae or patch on male S9 count: absent with distal setiferous patch/line continuous medially. Submedial projections on proximal margin of S9 count: absent. Cupula length vs. gonostyle–volsella complex length: cupula less than 1/2 the length of gonostyle–volsella complex in lateral view. Proximodorsal notch of cupula count: present. Proximodorsal notch of cupula shape: arched (inverted U-shape). Proximodorsal notch of cupula width vs length: wider than long. Proximolateral projection of the cupula shape: blunt. Gonocondyle count: present. Gonocondyle shape: acute. Distodorsal margin of cupula shape: concave. Distoventral submedian corner of the cupula count: absent. Dorsomedian projection of the gonostyle–volsella complex count: absent. Dorsomedian conjunctiva of the gonostyle–volsella complex count: present. Dorsomedian conjunctiva of the gonostyle–volsella complex length relative to length of gonostyle–volsella complex: dorsomedian conjunctiva not extending 2/3 of length of gonostyle–volsella complex in dorsal view. Dorsomedial margin of gonostyle–volsella complex shape: V-shaped. Proximal end of dorsomedian conjunctiva of the gonostyle–volsella complex shape: acute or V-shaped. Parossiculus count or parossiculus and gonostipes fusion: present and parossiculi not fused with the gonostipes. Medioventral conjunctiva of the gonostyle–volsella complex count or fusion of parossiculi: medioventral conjunctiva present and parossiculi independent or fused proximally.Apical parossicular setae count: one. Distal projection of the parossiculus count: absent. Distal projection of the penisvalva count: absent. Gonossiculus spine count: 2. Gonossiculus spine length: one spine not more than 2× as long as the other(s) (spines of similar lengths). Harpe length: harpe shorter than gonostipes in lateral view. Harpe shape: simple and not bilobed. Harpe orientation: medial. Lateral margin of harpe shape: widest point of harpe is at its articulation site with gonostyle–volsella complex. Distal margin of harpe in lateral view: acute or pointed. Lateral setae of harpe count: present. Lateral setae of harpe orientation: oriented distally. Lateral setae on harpe density: setae sparse. Dense patch of setae on the distoventral edge of the harpe count: absent. Distal setae on harpe length: setae of equal length across distal end of harpe. Distodorsal setae of sensillar ring of harpe length vs. harpe width in lateral view: setae as long as or shorter than harpe width. Distodorsal setae of sensillar ring of harpe orientation: distally. Sensillar ring area of harpe orientation: distomedially. Sensillar ring shape: circular. Distoventral margin of harpe in lateral view: straight.

Distribution. Holarctic.

Material Examined. Lectotype female: SWEDEN: MZLU Type No. 5329: 1 ( MZLU).

Non-type material (4 males, 3 females): CANADA: 1 male. PSUC _FEM 50307 ( AMNH). USA: Arizona: 1 female. PSUC _FEM 62155 ( TAMU). USA: California: 3 males, 1 female. PSUC _FEM 34290 ( TAMU); PSUC _ FEM 457080 ; UCRC _ ENT 00103613 , 00103617 ( UCRC). USA: Colorado: 1 female. INHS Insect Collection 14038 ( INHS) .

Figures

FIGURE 21. Conostigmus dimidiatus (Thomson, 1858) female lectotype (MZLU Type No. 5329). A. Lateral view. B. Dorsal view. Imaged by Christoffer Fägerström at the MZLU.

FIGURE 22. Conostigmus dimidiatus (Thomson, 1858) female lectotype (MZLU Type No. 5329) anterior view of the frons. Imaged by Christoffer Fägerström at the MZLU.

FIGURE 23. Conostigmus dimidiatus (Thomson, 1858) male genitalia. A. Ventral view (PSUC_FEM 34290). B. Lateral view (UCRC_ENT 00103613). C. Dorsal view (UCRC_ENT 00103613).