Brevulacus reticulatus Manson 1984

Chetverikov, Philipp E., Desnitskiy, Alexey G., Klimov, Pavel B., Ozman-Sullivan, Sebahat K., Romanovich, Anna E. & Sukhareva, Sogdiana I., 2023, Tuerkayana rotundum, Zoological Studies 62 (35), pp. 1-18 : 8-14

Brevulacus reticulatus Manson 1984

Brevulacus reticulatus Manson 1984: 87–88 , fig. 32–39 (protogyne), fig. 40–46 (deutogyne).

B. reticulatus Skoracka et al. 2005: 25 ; Xue et al. 2009b: 33; Ripka 2011: 133; Pye 2012: 61 .

Remarks: Manson (1984) found the type species, B. reticulatus , on Quercus sp. in three cities of New Zealand (Levin, Upper Hutt and Christchurch) and reported on its seasonal dimorphism. Since then this species has been recorded many times on Quercus spp. in different European countries and in China. According to Breitwieser et al. (2010), all oak species currently known from New Zealand are non-indigenous. Colonists introduced them, presumably from Europe most likely along with different associated symbionts, including B. reticulatus . Below we give supplementary data on the protogyne and deutogyne of B. reticulatus , based on material collected from Q. robur in North-West Russia.

PROTOGYNE (n = 10), supplementary description ( Figs. 4B , 5 , 6I, M–T ). Body fusiform, yellowish, 238–255, 83–89 wide at the level of seta c2. Prodorsal shield subtriangular, 42–47, 63–70 wide, with large apically notched smooth frontal lobe 10–12, 15–19 wide. Prodorsal shield ornamentation net-like with distinct cells between median, admedian and submedian lines. Median line complete, entire ( Figs. 4B , 5A, C ). Scapular setae sc 25–29, 33–37 apart, directed up and forward. Gnathosoma large, directed obliquely downward, 41–50, ep 3–4, d 10–13, ν 5–7, angled. Leg I 43–46, femur 11–13, bv 12–16; genu 5–7, l'' 33–40; tibia 9–10, l' 9–12; tarsus 7–8, u' 4–6, ft' 24–30, ft'' 26–32, solenidion ω 9–10 with small knob apically, empodium (em), 7–9, 8-rayed, each ray, except of the rays of apical pair, with 3 to 7 subrays ( Fig. 6M– T ). Leg II 40–43, femur 10–12, bv 10–14; genu 5–6, l'' 17–22; tibia 8–10; tarsus 7–8, u' 4–6, ft' 9–13, ft'' 27–31, solenidion ω 9–11 with small knob apically, empodium (em) 7–9, 7-rayed, similar to empodium I. Infracapitular plate rounded anteriorly, smooth, 11–12, 22–25 wide; sternal line distinct 9–11. Coxal plates striated. Setae 1b 14–18, 11–13 apart; 1a 26–33, 10–12 apart; 2a 58–70, 27–31 apart; 12–17 incomplete coxigenital annuli bearing microtubercles before epigynium. External genitalia. Genital coverflap subtriangular, smooth, 9–11, 31–35 wide, preceded by distinct ribbon-shaped pregenital plate (sensu Flechtmann et al. 2015; Fig. 5D , arrow); setae 3a 34–45, 23–25 apart. Opisthosoma with 49–57 microtuberculated dorsal annuli forming three faint longitudinal ridges and 87–107 microtuberculated ventral annuli. Setal lengths: c2 36–43, d 46–52, e 29–34, f 46–52, h1 4–5, h2 70–85, all opisthosomal setae, except c2 and h1, very thin in distal half; 18–22 annuli from the rear margin of coxa II to c2; 16–22 annuli between c2 and d; 13–16 annuli between d and e; 35–41 annuli between e and f; 5–6 annuli between f and h2. Paired cuticular tubes associated with rectum (the elements of anal secretory apparatus, sensu Chetverikov et al. 2019) were clearly visible under the telosomal cuticle in all studied protogynes (not shown).

Male (n = 6): Body shape similar to protogynes but notably shorter, 178–202, 70–73 wide at the level of seta c2. Prodorsal shield ornamentation similar to those in protogynes. Opisthosoma with 51–56 dorsal and 81–87 ventral annuli. Genital area 12–15, 20–24 wide; 3a 22–26, 17–19 apart; eu 0.5–1. Paired cuticular tubes associated with rectum (the elements of anal secretory apparatus sensu Chetverikov et al. 2019) were observed in all studied males (not shown).

GenBank data (protogynes): ON920307 (Cox 1).

Material examined: Numerous adults collected on 10 June 2022 from the lower surfaces of leaves of Quercus robur L. ( Fagaceae ) in RUSSIA: Leningrad Prov., Gatchina distr., vil. Vyritza, coll. P.E. Chetverikov, slide series, mites in vials with 96% ethanol. All slides and ethanol material have been deposited in the Acarological Collection of ZIN RAS (Saint-Petersburg, Russia).

Remarks: The protogynes in our study are very similar to those described by Manson (1984) from New Zealand, except that our specimens have a larger number of ventral annuli (87–107 vs. 70–76, respectively) and longer prodorsal shield (42–47 vs. 31–39, respectively); the difference between the prodorsal shield measurements is possibly because our measurements include the length of the frontal lobe but Manson’s measurements do not.

DEUTOGYNE (n = 8, Figs. 6A–H, J–L , 7 ). Body elongated in comparison to protogynes, dark orange or brownish, 250–268, 73–80 wide at the level of seta c2. Prodorsal shield subtriangular, 40–46 (including frontal lobe), 53–59 wide, with large apically notched ribbed frontal lobe 12–14, 12–15 wide. Ornamentation of prodorsal shield varies ( Fig. 6A, B, C , Fig. 7A, B ): in some deutogynes it is almost smooth, in others indistinct traces of longitudinal lines and cells between them can be seen; however, in all cases the ornamentation notably less developed than in protogynes. Scapular setae sc 14–18, 28–32 apart. Gnathosoma large, directed obliquely downward, 39–44, ep 4–5, d 10–13, ν 5–7. Leg I 38–42, femur 11–12, bv 15–18; genu 6–7, l'' 25– 31; tibia 9–10, l' 7–12, tarsus 6–7, u' 3–4, ft' 17–23, ft'' 25–33, solenidion ω 8–9 with indistinct knob apically, empodium (em) 7–8, 6-rayed, each ray, except for the rays of apical pair, with 3 to 7 subrays. Leg II 35–38, femur 10–12, bv 14–18; genu 5–6, l'' 12–16; tibia 8–9; tarsus 6–7, u' 3–4, ft' 6–9, ft'' 23–30, solenidion ω 8–10 with indistinct knob apically, empodium (em) 7–8, similar to empodium I. Infracapitular plate rounded anteriorly, smooth, 14–16, 21–25 wide; sternal line distinct 10–12. Coxal plates striated, setae 1b 8–11, 9–11 apart; 1a 28–35, 9–11 apart; 2a 38–47, 29–32 apart; 18–23 incomplete coxigenital annuli bearing microtubercles before epigynium. External genitalia. Genital coverflap subtriangular, smooth, 10–13, 26–29 wide, preceded by indistinct ribbon-shaped pregenital plate (sensu Flechtmann et al. 2015); setae 3a 34–48, 23–26 apart. Opisthosoma with 42–50 smooth dorsal annuli forming faint longitudinal median ridge and 56–71 ventral annuli bearing round microtubercles that are notably larger than those on coxigenital annuli ( Fig. 7E ). Every second dorsal annulus thickened in posterior half or in almost whole opisthosoma ( Fig. 7C, D ). Setal lengths: c2 29–36, d 47–58, e 24–37, f 33–38, h1 4–5, h2 50–60; all opisthosomal setae except f and h1 very thin in distal half; 9–12 annuli from the rear margin of coxa II to c2; 10–14 annuli between c2 and d; 11–14 annuli between d and e; 22–26 annuli between e and f; 4–6 annuli between f and h2. Paired tubes associated with rectum (the elements of anal secretory apparatus sensu Chetverikov et al. 2019) were clearly seen in all studied deutogynes ( Fig. 7F ).

GenBank data (deutogynes): ON920308 (Cox 1).

Material examined: Sparse females collected on 6 June 2022 from the lower leaf surface of Quercus robur L. ( Fagaceae ) in RUSSIA: Leningrad Prov., Gatchina distr., vil. Vyritza, coll. P.E. Chetverikov, slide series, mites in vials with 96% ethanol. All slides and ethanol material have been deposited in the Acarological Collection of ZIN RAS (Saint-Petersburg, Russia).

Remarks: The deutogynes from our material were very similar to those described by Manson (1984) from New Zealand, except that our specimens were notably longer (250–268 vs. 159–216).

Barcode date, blast search results and sequence comparison

The Cox1 sequences of protogynes (collected in July 2021, ON920305, 648 bp, n = 2) and deutogynes of S. serrata (collected in April 2022, ON920306, 657 bp, n = 1) from A. platanoides were identical. Also, the Cox1 sequences of protogynes (collected in June 2022, ON920307, 619 bp, n = 3) and deutogynes (collected in May 2022, ON920308, 631 bp, n = 3) of B. reticulatus collected from Q. robur contained the same four degenerated sites (Y) and were identical in all other nucleotide positions.

Nucleotide blast (BLASTN) search for our S. serrata sequences (ON920305 and ON920306) revealed the sequence OK489799 ( S. serrata ) and series of sequences MZ482237–MZ482243 ( Aculops sp. ) to be the closest, with the highest values for percent identity (98.4–99.5%) and coverage (96–99%). Also, a protein blast (BLASTX) search for S. serrata returned 100% identical sequences UOK10252 and UOK10253 ( Aculops sp. ) and UCS82605 ( S. serrata ). Considering our data on seasonal morphological dimorphism (see above) and BLAST results, Aculops sp. could be a deutogyne of S. serrata .

Nucleotide blast (BLASTN) search for our B. reticulatus sequences (ON920307 and ON920308) revealed a large group of moderately similar (79–87% identity) sequences of rhyncaphytoptines of the genera, Rhyncaphytoptus , Diptilomiopus and Brevulacus , from China, with the highest value for percent identity being 87.54% for sequence MZ483311 of R. albus , and the lowest value of 79.11% for sequence MZ482490 of B. reticulatus . Protein blast (BLASTX) search for our B. reticulatus sequences revealed largely the same group of similar sequences, with highest amino acid composition identity ranging from 98.56% to 99.52% in sequences of R. albus (UOK11311), Diptilomiopus hexogonus (UOK10706) and B. reticulatus (QVU25232).

Remarks: The pairwise identity of the Cox1 sequences confirmed the conspecificity of morphologically different seasonal forms of both S. serrata and B. reticulatus . In addition, molecular based identification of B. reticulatus produced unexpected results, in that sequences of conspecifics from GenBank were less similar to our sequences than sequences of a non-conspecific, Rhyncaphytoptus albus . Morphologically, B. reticulatus and R. albus clearly differ in ornamentation of the female genital coverflap: smooth in B. reticulatus and with about 18 longitudinal ribs in R. albus ( Keifer 1959, p. 17, fig. 13). Since our specimens were clearly closer to B. reticulatus than to R. albus , it is necessary to verify the identifications of the rhyncaphytoptine mites from GenBank prior to drawing further conclusions.

Field observations

Figures

Fig. 4. Prodorsal shields in females of Brevulacus reticulatus Manson 1984 (protogyne, A, from original description. B, this paper), B. extensus Pye 2012 (C), Rhyncaphytoptus salicinus (Soika et al. 2017) n. comb. (D), B. albus (Keifer 1959) n. comb. (E), B. atlanticus (Keifer 1959) n. comb. (F), B. carpathicus Ripka 2011 (G), and B. jilinensis Xue, Song & Hong 2009 (H). All except figure 4B redrawn from original descriptions.

Fig. 5. DIC microphotographs of protogyne of Brevulacus reticulatus Manson 1984. A, dorsal view of body. B, ventral view of body. C, prodorsal shield. D, genital area (arrow indicates pregenital plate). Note: setae sc in live mites are directed anteriad (Fig. 5A), in contrast to many slide-mounted mites with artifact backward directed sc (Fig. 5C). Scale bars: A, B = 40 µm; C, D = 15 µm.

Fig. 6. Drawings of deutogyne (A–H, J–L) and protogyne (I, M–T) of Brevulacus reticulatus. A–C, prodorsal shield ornamentation. D, internal genitalia (deutogyne). E, coxigenital area. F, dorsal view of entire deutogyne. G and H, legs I & II. I, empodium I (protogyne). J, empodium I (deutogyne). K and L, tarsal solenidia II & I (deutogyne). M–T, terminal (M) and lateral (N–T, from distal to proximal) empodial rays (protogyne). Scale bars: A–D = 15 µm; E = 30 µm; F = 60 µm; G, H = 10 µm; I–L = 5 µm; M–T = 2 µm.

Fig. 7. DIC microphotographs of deutogynes of Brevulacus reticulatus Manson 1984. A and B, prodorsal shield in two deutogynes. C and D, dorsal view of two deutogynes differing in the appearance of dorsal opisthosomal annuli. E, genital area, F, paired tubes (arrows) of anal secretory apparatus. Scale bars: A, B, E = 15 µm; C, D = 40 µm; F = 10 µm.