Myrmozercon brachiatus ( Berlese, 1903 )

Khalili-Moghadam, Arsalan & Babaeian, Esmaeil, 2023, Rediscovery of Myrmozercon brachiatus Berlese (Acari: Mesostigmata) in south-west Iran, Persian Journal of Acarology 12 (2), pp. 199-209 : 201-206

Myrmozercon brachiatus ( Berlese, 1903)

Myrmonyssus brachiatus Berlese, 1903: 17 .

Myrmonyssus brachiatus . Berlese 1904: 441; Vitzthum 1930: 89; Hunter and Hunter 1963: 335. Myrmozercon brachiatus . Rosario and Hunter 1988: 470; Joharchi and Moradi 2013: 252; Joharchi et al. 2015: 558.

Materials examined

Specimens were collected from Chaharmahal va Bakhtiari Province, Ben county (Larak) (32° 35' 12" N, 50° 40' 22" E, 2406 m a.s.l.) from nest of Messor mediosanguineus Donisthorpe, 1946 ; coll. A. Khalili-Moghadam, 07 April 2022.

Specimen's deposition

Two females have been deposited in the Acarological Laboratory, Plant Protection Department, Agricultural College, Shahrekord University ( APAS), Iran.

Diagnosis (female)

Dorsal shield ovoid-angulate and mostly smooth, with 36 pairs of smooth setae, five pairs of Jseries setae (J1-J5); soft cuticle around and posterior margin of dorsal shield smooth (lacking striae); dorsal cuticle not hypertrichous; sternal shield with indistinct posterior margin, lateral margins slightly sclerotized; shape of genital shield distinctive (strongly constricted after insertion of setae st5, with two parts, first part wide, from anterior to slightly after st5 and second part narrow, from slightly after st5 to posterior margin); metapodal plates absent; anal shield triangular; peritremes short, peritrematal shields and pores absent; opisthogastric soft integument with 10 pairs of smooth setae; moveable and fixed digit of chelicerae with two and one small teeth respectively, pilus dentilis and cheliceral seta absent; epistome smooth arc-shaped (edentate), corniculi short, irregularly formed; subcapitular groove with seven rows of denticles, with 7–9 denticles per row; palp coxal seta present, simple; tarsi with rudimentary claws and distinct pulvillus; leg I longer (390–434) than all other legs (leg II 285–320, leg III 222–275, leg IV 368–397); setal counts of legs I–IV (from coxa to tibia): 2- 5-10-13-14; 2-5-10-11-10; 2-5-6-8-8; 1-5-6-7-9; genu IV with seven setae (pl absent).

Redescription (female) Dorsal idiosoma ( Figs. 1 , 4 ) – Idiosoma 427–459 long and 300–336 wide; dorsal shield ovoidangulate, 415–439 long, width at level of setae S3, 285 –305, smooth medially, with uneven lineate-reticulate ornamentation on anterolateral areas, shield with 36 pairs of setae 19 pairs on podonotal area (j1–6; z1–2; z4–6; s1–6; r3–4) and 17 pairs on opisthonotal region (J1–5, Z1–5, S1–5), including PX2 between J3 and Z3 and PX3 between J3 and J4, and r6 located on ventral side opposite to coxae IV, and at about eight pairs of discernible pore-like structures, pores near the base of j1 absent. Dorsal shield setae smooth, slightly thickened at the base (length 5–48) ( Figs. 1, 3 ), opisthonotal setae longer than podonotal setae, S5 and Z5 longest and z1 shortest. Lengths of podonotal setae: j1 17 – 20, j2 10– 12, j3 7–10 shorter than other setae in series, j4 19–20, j5 17–20, j6 27–30; z1 5–7 shorter than other setae, z2 10–12, z3 lacking, z4 22–24, z5 27–30, z6 32–34; s1 10 –12, s2-3 14–17, s4 22 –24, s5 34 – 37, s6 34 –37, r3 15–16, r4 17–20 and r6 11–13. Lengths of opisthonotal setae: J1 31–34, J2-3 34– 37, J 4 27–30, J5 12–15; Z1 -2 34–37, Z3 32–34, Z4 34–37, Z5 46–48; S1 -2 (34–37), S3 (39–42), S4 (31–34), S5 (44–47), PX2 (36–39), PX3 (31–34).

Ventral idiosoma ( Figs. 5–6 ) – Tritosternum with short columniform base (17–19) and pilose laciniae (53–56). Sternal shield sparsely lineate-reticulate on anterior, median surface smooth, 93–97 long (at level of slightly after st3), 120–127 wide (at level of projection between coxae II – III) and 78–82 between st1 and st2, with a deep notch anteromedially at level of tritosternum placement; posterior margin unrecognizable. Sternal setae short and smooth, with tips not reaching bases of the following ones, st1 (19–22) and st2-3 (14–17); lyrifissures iv1 and iv2 slit-like located slightly behind setae st1 and between st2-st3 respectively. Metasternal setae (st4 12–15) on soft cuticle, lyrifissures iv3 absent or obscure; endopodal platelets II-III and III-IV narrow and fused to lateral margins of sternal shield. Epigynal shield pad-shaped, narrowing conspicuously posterior of st5, 175–180 long and 88–93 wide at widest point (middle of wide part 122–125 long, above the insertion of st5) and 25–27 at narrowest point (middle of narrow part 53–55 long), anterior hyaline margin rounded, extending to level of st3; narrow portion with rounded posterior margin, genital setae st5 10–12, placed on posterolateral margins of wide portion and associated lyrifissures iv5 on soft integument, slightly behind st5. Anal shield 76–83 long (with cribrum) and 82–85 wide, triangle-shaped, punctatereticulate on lateral portion, median surface smooth; postanal setae 22–25 long, slightly thicker and shorter than para anal setae (24–27); cribrum with a narrow band of spicules, anal gland pores (gv3) absent or obscure. Lateral and opisthogastric soft integument with 10 pairs of smooth setae, R setae (12–14), ZV1 (11–13), ZV2 (13–15), ZV3-4 (12–14), ZV5 (24–26), JV1 (11–13), JV5 (25–28), with one pair of ventral pores near ZV3, other ventral pores obscure or absent. Metapodal plates absent. Peritreme short, extending just beyond the posterior margin of coxa II, peritrematal plate absent.

Exopodal platelet narrow and curved behind coxae IV. Stigma located between coxae III-IV.

Gnathosoma ( Fig. 7 ) – Epistome ( Fig. 2 ) smooth, edentate, arc-shaped. Corniculi short, irregularly formed, horn-like, shorter than internal malae; internal malae with a pair of adjacent median projections, and pair of sparsely dentate projections at lateral edges. Labrum acuminate, pilose, conspicuously longer than internal malae. Deutosternal furrow on ventral subcapitulum with seven transverse rows of denticles, each with 7–9 denticles. Lengths of hypostomal and palpcoxal setae: h1, h3 and pc 14–16, h2 7–9. Chelicerae ( Fig. 8 ) typical for genus, moveable digit (21–25) with two small teeth, middle article (53–58) ending in fixed digit (7–10) with a single small tooth, pilus dentilis and cheliceral seta absent. Palp (78–83), chaetotaxy normal, (sensu Evans and Till 1966), with simple setae; palp apotele two-tined ( Fig. 7 ) with 19–22 long from base to anterior tip of longer fork.

Legs ( Figs. 9–12 ) – Tarsi I –IV each with rudimentary claws and distinct pulvillus. Lengths of legs: leg I 390–434, leg II 285–320, leg III 222–275 , leg IV 368–397. Coxae I –IV: 2 (0 0/1, 0/1 0), 2 (0 0/1, 0/1 0), 2 (0 0/ 1, 0/1 0), 1 (0 0/1, 0/0 0); trochanters I–IV: 5 (1 0/1, 0/2 1), 5 (1 0/1, 0/2 1), 5 (1 1/1, 0/2 0), 5 (1 0/2, 0/1 1); femora I–IV: 10 (2 2/1, 2/1 2), 10 (1 3/1, 2/2 1), 6 (1 2/0, 1/1 1), 6 (1 2/1, 1/0 1); genu I–IV: 13 (2 3/2+1, 3/1 2) (+1 only on right leg in one specimen), 11 (2 3/1, 2/1 2), 8 (2 2/1, 1/1 1), 7 (2 2/1, 2/0 0)); tibiae I–IV: 14 (2 3/3, 3/1 2), 10 (2 2/1, 2/1 2), 8 (2 1/1, 2/1 1), 9 (2 1/1, 2/1 2); tarsi II–IV: 18 (3 3/2, 3/2 3 + mv, md). Seta ad on trochanter III, pd1–2 and pl1 on femur I, ad1 on femur I–IV, pl1–2 on genu I thicker than other setae. Genu I with a supernumerary seta on right leg in only one specimen .

Male – Unknown. Remarks

Myrmozercon brachiatus differs from all congeners by the presence of combination characters as follows: five pairs of J-series setae (J1-J5), shape of the genital shield (strongly constricted after insertion of setae st5), sternal shield with a deep notch anteromedially at level of tritosternum placement, with indistinct posterior margin, lateral margins slightly sclerotized, and genu IV with seven setae (pl absent). In addition, we studied detailed photomicrographs of three females on the slides (Nos. 6M/1, 6M/2, M5/50) of the Berlese Acaroteca deposited in Florence, Italy .

In the original description and illustration of M. brachiatus ( Berlese, 1904, Figs. 156–157), anterior margin of sternal shield without notch, setae st5 are obviously absent, there are two unpaired setae on dorsal shield, and setae J5 absent but these were all inaccurate, and in the all detailed photomicrographs we studied, anterior margin of sternal shield was with notch, setae st5 present (in 6M/1 and 6M/2 slides, from personal notes of Peter Mašan), dorsal shield without unpaired seta between J-series and setae J5 are obviously present.

By comparing the description of Berlese (1904, Figs. 156–157) and our observations on Iranian specimens, we could find small differences in some characters as follows:

In our Iranian specimens, genital shield was slightly wider than Berlese's specimens and podonotal setae significantly shorter than opisthonotal setae ( Figs. 1 , 4 ), but in type specimens, podonotal setae were longer, however still shorter than opisthonotal setae. In Iranian specimens, there are eight pairs of ventral setae, but 10 pairs in Berlese's specimens (see Fig. 156 in Berlese 1904). We believe that such morphological differences may represent intraspecific variation in two different geographical zones.

Moreover, M. brachiatus was collected by Berlese (1903) from the nest of Messor barbarus capitatus var. minor ( Hymenoptera : Formicidae ). Now, this ant species is Messor capitatus (Latreille, 1798) which has been raised to the species level from the subspecies level. On other hand, Iranian specimens were collected from the nest of Messor mediosanguineus Donisthorpe, 1946 , which previously was Messor barbarus mediosanguineus Donisthorpe, 1946 . This ant subspecies was raised to the species level by Khalili-Moghadam et al. (2019). So, this subject shows that Myrmozercon is rightly thought to be host-specific. Hence, probably the taxonomic changes in ants are reflected by the species of Myrmozercon living with them. To date, 27 species of Myrmozercon have been described globally ( De Moraes et al. 2022), many of which are known only from their type material.

Given that the morphology-defined species boundaries have been ambiguous, there has been much disagreement on species placement, especially since there is little information about the type species of the genus Myrmonyssus .

The specimens of M. brachiatus from Iran are the first to be reported in the literature after more than one hundred years since this species was described by Berlese (1903). The discovery of M. brachiatus in south-west Iran expands the previously documented distribution range of this species by about 3400 km to the east. Although the laelapid fauna of Iran is relatively well studied, there are still some understudied regions. A more complete knowledge of the diversity of the laelapid mite in the country could be revealed only after carrying out further studies in these poorly-examined regions.

Figures

Figures 1–3. Myrmozercon brachiatus (female) – 1. Dorsal idiosoma; 2. Epistome; 3. A dorsal seta.

Figures 4–5. Photographs of Myrmozercon brachiatus (female) – 4. Dorsal idiosoma; 5. Ventral idiosoma.

Figures 6–8. Myrmozercon brachiatus (female) – 6. Ventral idiosoma; 7. Ventral gnathosoma with palp; 8. Chelicera.

Figures 9–12. Myrmozercon brachiatus (female) – 7. Leg I; 8. Leg II; 9. Leg III; 10. Leg IV.