Amblyseius obtuserellus Wainstein & Begljarov, 1806

Fang, Xiao-Duan, Nguyen, Van-Liem, Ouyang, Ge-Cheng & Wu, Wei-Nan, 2020, Survey of phytoseiid mites (Acari: Mesostigmata, Phytoseiidae) in citrus orchards and a key for Amblyseiinae in Vietnam, Acarologia 60 (2), pp. 254-267 : 255-257

Amblyseius obtuserellus Wainstein & Begljarov

( Figs. 1 a – e )

Amblyseius obtuserellus Wainstein & Begljarov, 1971: 1806 ; Ehara & Yokogawa 1977: 54; Wainstein 1979: 14; Wu 1980: 44; Moraes et al. 1986: 24; Ryu & Lee 1992: 28; Wu et al. 1997: 50; Wu et al. 2009: 194.

Amblyseius (Multiseius) obtuserellus , Denmark & Muma 1989: 124.

Description — Female (n = 8)

Dorsum — Idiosomal setal pattern: 10A: 9B/JV-3: ZV. Dorsal shield smooth ( Fig. 1a ), 317 (300–330) long and 200 (185–218) wide, distances between setae j1- J5 303 (289–316) and s4-s4 176 (164–186), shield nearly oval, constricted at level of R1. Setae r3 and R1 on soft membranous cuticle laterad dorsal shield, r3 at level of z4, R1 at level of shield incisions. All setae smooth, except Z4, Z5 with minute thorns. With seven pairs of solenostomes (gd1, gd2, gd4, gd5, gd6, gd8, gd9) on dorsal shield. Length of setae: j1 24 (23–26), j3 43 (40–46), j4 5 (4–6), j5 5 (4–6), j6 6 (4–8), J2 7 (5–9), J5 6 (4–7), z2 9 (7–11), z4 9 (7–11), z5 5 (4–6), Z1 7 (6–9), Z4 82 (75–88), Z5 161 (155–167), s4 68 (63–72), S2 8 (7–9), S4 7 (6–9), S5 7 (5–8), r3 12 (11–14), R1 8 (7–9).

Venter — ( Fig. 1b ). All ventral setae smooth. Sternal shield with sparse striation, anterior margin convex, posterior margin slightly concaved, 69 (68–71) long, 74 (73–75) wide, wider than long, with three pairs of setae st1 31 (29–33), st2 28 (25–32), st3 26 (24–30), and two pairs of lyrifissures (pst1-pst2), distance between st1-st3 55 (53–58) and st2-st2 68 (67–69). Metasternal platelets drop-shaped, each with one metasternal seta, st4 25 (24–26) and one lyrifissure (pst3). Genital shield smooth, with one pair of thin genital setae st5 27 (25–28), distance between st5-st5 59 (64–71); one pair of associated poroids on soft cuticle near posterior corners of shield. Ventrianal shield nearly pentagonal, 112 (105–116) long, 82 (76–88) wide at level of ZV2, 78 (73–84) wide at level of anus, with three pairs of thin pre-anal setae JV1 16 (14–19), JV2 14 (11–17), ZV2 12 (10–13); Pa 14 (12–17), Pst 16 (14–19) long. Pre-anal pores crescentic, posteromedian to JV2, distance between pores 21 (19–23). Opisthogastric soft cuticle with four pairs of setae, ZV1 14 (13–16), ZV3 9 (7–10), JV4 8 (6–9), JV5 59 (54–64) long. All ventral setae thin, except JV5, thicker. Two pairs of metapodal platelets, primary platelets 19 (17–21) long, 5 (3–5) wide, secondary ones 11 (10–12) long, 2 (1–2) wide.

Peritremes — Peritremes extending anteriorly between j1.

Chelicerae — ( Fig. 1c ). Fixed digit 32 (30–36) long, with 11 teeth, movable digit 28 (27–30) long, with four teeth.

Spermatheca — ( Fig. 1d ). Calyx of spermatheca tubular, 25 (22–28) long, the proximal part mostly distal part thicker, granular surface, 9 (8–10) long, 2 (2–2) wide at the junction with the vesicle, atrium and major duct indiscernible.

Legs — Genua formula for leg I 2 – 1/2, 2/1– 1, leg II 0 – 2/1, 0/2 – 2, leg III 1 – 1/2, 1/2 – 0, leg IV 2 – 2/1, 0/1 – 1. Genua I-III each with one macroseta, Sge I 32 (29–34), Sge II 31 (28–32), Sge III 42 (39–45). Leg III with one macroseta on tibia, Sti III 30 (27–32). Leg IV ( Fig. 1e ) with three macrosetae on genu, tibia and basitarsus, Sge IV 82 (76–86), Sti IV 46 (40–51) and St IV 59 (56–62).

Specimens examined — 8 ♀♀, Chau Thanh district, Ben Tre Province (accession no. BT-0190, BT-0200, BT-0211, BT-0212, BT-0220, BT-0231, BT-0232, BT-0240), on Citrus reticulata × sinensis, 10 IV 2018, Fang X.D. coll.

Previous records — China, Japan, Russia, South Korea.

Remarks — Amblyseius obtuserellus holotype specimen was from the Primorsky Territory, U.S. S.R. (Wainstein and Begljarov, 1971; Denmark and Muma, 1989). This species was also recorded in Japan ( Ehara and Yokogawa, 1977) and South Korea ( Ryu and Lee, 1992). A. obtuserellus have been found in many Provinces in China, including Jiangsu, Zhejiang, Anhui, Fujian, Jiangxi, Hunan and Guangdong. Wu (1982) reported that the size of its genital shield, ventrianal shield and distance between pre-anal pores are variable, but the calyx shape of spermatheca does not present differences. The calyx of the spermatheca in this species is cylindrical and long and the distal part of calyx thickened and more sclerotized.

Ehara and Yokogawa (1977), Denmark and Muma, 1989, Ryu and Lee (1992) and Wu et al. (2009) re-described this species. Geographical populations in different countries all have distinctive, granular spermathecal cervix, but they have differences in the individual size, length of some setae on dorsal shield and the macrosetae on Leg IV, and the length of cervix of spermatheca. Their measurements differences are listed in Table 1.

Amblyseius obtuserellus has 11 well-developed teeth on fixed digit and four teeth on movable digit of the chelicerae and this species may play an important role in bio-control. Its biology and bio-control application need to be further studied.

Figures

Figure 1 Female of Amblyseius obtuserellus. a – Dorsal shield; b – Ventral idiosoma; c – Chelicera; d – Spermatheca; e – Leg IV, genu- basitarsus.