Introduction

The family Acarophenacidae currently consists of 7 genera (six extant and one fossil) and about 37 described species worldwide (Arjomandi et al. 2017; Walter & Seeman 2017; Khaustov & Abramov 2018). Only one species of this family, Acarophenax mahunkai Steinkraus and Cross, 1993, was recorded from China (Gao & Zou 1994). Acarophenacid mites are known as egg parasitoids of various insects, including beetles (Cerambycidae, Tenebrionidae, Nitidulidae, Dermestidae, Curculionidae, Mycetophagidae and Erotylidae) and thrips (Thysanoptera) (Goldarazena et al. 2001; Katlav et al. 2015; Arjomandi et al. 2017; Walter & Seeman 2017; Khaustov & Abramov 2018), and considered as potential biological control agents due to its non-toxicity to people or domesticated animals (Krantz & Walter, 2009).

The genus Paracarophenax resembles Aethiophenax, but can be easily distinguished by stigmatal openings dorsal, atria membranous; one or two pairs of setae on tergite EF, setae e present or absent; and setae ps present or absent (stigmatal openings lateral, atria sclerotized; one pair of setae on tergite EF, setae e absent; and setae ps absent in Aethiophenax) (Walter & Seeman 2017). Paracarophenax comprises 7 described species: P. dybasi Cross, 1965, P. bambergensis (Krczal, 1959), P. undosus Mahunka, 1975, P. paucisetosus Mahunka and Rack, 1977, P. scolyti Khaustov, 1999, P. myzognathus Walter and Seeman, 2017 and P. triplaxophilus Khaustov and Abramov, 2017. In this paper, we describe and illustrate a new species associated with Monochamus alternatus Hope (Coleoptera: Cerambycidae). This is the second report of the family Acarophenacidae from China. An updated key to species of Paracarophenax is also provided.

Materials and methods

The beetle hosts Monochamus alternatus were captured in trap devices set up in Minhou county, Fuzhou city, Fujian province, China. The trapped beetles were examined and then the phoretic mites were transferred into 70% ethanol under a stereo microscope. All acarophenacid mites removed and cleared in lactic acid, and mounted in Hoyer's medium. Specimens were examined at 400x and 1000x magnification by using differential interference contrast of a Leica DM5000B compound microscope.

All measurements in micrometers (µm) were taken from slide-mounted specimens using a stage-calibrated ocular ruler. Measurement data are presented for holotype, followed by ranges for paratypes in parentheses. Body length was measured from the anterior margin of the idiosoma (including gnathosoma) to the posterior margin of the opisthosoma, and body width was measured as the greatest distance posterior to coxae II. Setal lengths were measured from the center of the setal base to the tip of the seta; distances between setae were measured as the distance from the center of one setal base to that of the other. Legs were measured from the basal end of trochanter to the distal end of tarsus (excluding pretarsus). Terminology follows Katlav et al. (2015) and Walter & Seeman (2017) who adapted from Lindquist (1986).

Description

Adult female (n=25).

Gnathosoma (Fig. 2). Rounded, fused with idiosoma. Palps fused with gnathosomal capsule, one pair of setae laterally, length 3 (3–4). Cheliceral stylets 12 (12–14) strong and curved. Pharynx enlarged and almost elliptical, length 50 (46–52), width 14 (12–15).

FIGURE 1.

Paracarophenax alternatus Xu and Zhang sp. nov. (adult female). dorsal view of the body.

Idiosomal dorsum (Fig. 1). Ovate, length 255 (225–255), width 115 (100–115). Prodorsal shield trapezoidal, with two pairs of setae (v₂ and sc₂) thickened and blunt-ended; Lengths of setae: v₂ 50 (40–50), sc₂ 39 (33–40); distances between setae: v₂–v₂ 30 (27–30), v₂–sc₂ 30 (25–31), sc₂–sc₂ 77 (72–77). Stigmata on prodorsal projection, associated with tracheal system and atria, tracheal trunks with a brush-like atrium. Cupules ia, im and ih situated on tergites D, EF and H, respectively. One pair of crescent-shaped ornamentation located near posterior margin of tergites C and middle of tergites D, respectively. Tergite C with two pairs of setae (c₁ and c₂); tergite D with one pair of setae d; tergite EF with two pairs of setae (e and f); tergite H with two pairs of setae (h₁ and h₂); all dorsal setae thickened and blunt-ended except h₂ thinner and pointed. Setae f about twice as long as e; setae v₂, c₁ and f subequal, setae sc₂, c₂ and d subequal in length, and about four-fifths as long as setae f; setae h₂ about two-thirds of h₁ and located very close to h₁. Setal lengths: c₁ 48 (43–50), c₂ 37 (30– 37), d 37 (35–43), e 22 (17–26), f 45 (36–49), h₁ 30 (20–30), h₂ 17 (13–18); distances between setae: c₁–c₁ 50 (45–50), c₂–c₂ 115 (100–115), c₁–c₂ 40 (35–40), d–d 60 (55–60), e–e 56 (47–56), f–f 22 (20–26), e–f 15 (12–17), h₁–h₁ 32 (25–32), h₂–h₂ 40 (33–40), h₁–h₂ 5 (3–5).

Idiosomal venter (Fig. 2). Ventral plates smooth. All ventral setae thin and smooth, lengths of setae: 1a 7 (5–7), 2a 12 (11–15), 3a 21 (20–28), 3c 12 (10–15), 4a 10 (8–12), 4b 8 (7–10), 4c 8 (8–10); distances between setae: 1a–1a 58 (50–58), 2a–2a 40 (38–42), 3a–3a 42 (33–42), 4a–4a 26 (23–30). All ventral apodemes well developed except for apodemes 3 (ap3) which are short and reach the bases of setae 3c. Apodemes 1 (ap1), apodemes 2 (ap2) and sejugal apodeme (apsej) joined with prosternal apodeme (appr); ap1 fused with appr to form a Y-shaped structure with anterior branches surrounding the base of gnathosoma. Posterior margin of posterior ventral plate with well developed tegula. Aggenital plate without setae ag; plate PS with one pair of setae ps, 6 (4–6).

FIGURE 2.

Paracarophenax alternatus Xu and Zhang sp. nov. (adult female). ventral view of the body.

Legs (Figs. 3–4). Lengths of legs I–IV: 75 (70–77), 72 (70–75), 87 (85–95), 100 (92–100). Tibiotarsus I length 39 (35–40), width 22 (20–23). Setal counts for legs I–IV (trochanter to tarsus): 1-3-4-17 +ϕ+ω+tarsal-claw complex, 1-3-1-4+ϕ-6+ω, 1-2-1-4-6, 1-0-1-4-6.

Leg I (Fig. 3A): Trochanter: seta v′ comparatively short. Femur: setae l′ and v″ setiform, d weakly barbed and blunt-ended, 48 (45–50). Genu: setae l′ and l″ thickened and blunt-ended, v′ and v″ setiform. Tibiotarsus: 6 of 17 tibiotarsal setae are tibial (d, k, l′, l″, v′, v″) and 11 setae are tarsal (p′, p″, pl′, pl″, pv′, pv″, s, tc′, tc″, ft′, ft″); solenidion ϕ 10 (8–9), ω 8 (7–8); eupathidial setae p′, p″,ft′, ft″ tc′ and tc″ blunt-ended; seta d attenuated and whip-like, 87 (78–90); seta pl′ 53 (48–53) about twice as long as pl″ 27 (23–28); eupathidial seta k, 15 (13–15); seta v″ whip-like, 54 (48–55), almost 3.5 times as long as v′ 15 (14–16); setae l′, l″, pv′ and pv″ smooth and setiform.

Leg II (Fig. 3B): Trochanter: seta v′ slender and short. Femur: setae l″, v″ and d setiform. Genu: seta v′ spine-like, 8 (7–8). Tibia: solenidion ϕ 3 (3–5); setae d, v′ and l′ attenuated and whip-like, 70 (65–72), 50 (46–51) and 41 (38–44), respectively; seta v″ spine-like, 8 (7–8). Tarsus: solenidion ω 4 (3–5); seta tc″ attenuated and whip-like, 35 (30–38); setae pl″ and pv″ spine-like, 8 (7–8) and 10 (9–10), respectively; setae u′ and u″ slender and hard to discern.

FIGURE 3.

Paracarophenax alternatus Xu and Zhang sp. nov. (adult female, right side legs in dorsal view). A, leg I; B, leg II.

Leg III (Fig. 4A): Trochanter: seta v′ slender and pointed. Femur: setae d and v″ slender and pointed. Genu: setae v′ slender and pointed. Tibia: seta d attenuated and whip-like, 87 (80–87); setae v′ v″ and l′ slender and pointed. Tarsus: seta pv″ spine-like, 7 (6–7); seta tc″ attenuated; setae pv′ pointed and pl″ blunt-ended; setae u′ and u″ as on tarsus II.

Leg IV (Fig. 4B): Trochanter: seta v′ slender and pointed. Femur: nude. Genu: seta v′ slender and pointed. Tibia: setae d, v′ and v″ attenuated and whip-like, 94 (83–96), 42 (39–43) and 46 (40–46) respectively; seta l′ slender and pointed. Tarsus: seta pv″ spine-like, 8 (7–8); seta tc″ attenuated; setae pv′ and pl″ pointed; setae u′ and u″ as on tarsus II.

Etymology. The species name refers to the specific name of the host beetle, Monochamus alternatus Hope (Coleoptera: Cerambycidae) on which it was collected.

Remarks. On live specimens, the body of Paracarophenax alternatus Xu and Zhang sp. nov., looks yellowish-brown with a shiny appearance; phoretic mites were found distributed around the coxal cavity of the adult of Monochamus alternatus, cramping the host setae by hook-like claws on legs I (Fig. 5). It was observed feeding on the eggs of the host beetles (Fig. 6).

FIGURE 4.

Paracarophenax alternatus Xu and Zhang sp. nov. (adult female, right side legs in dorsal view). A, leg III; B, leg IV.

Differential diagnosis: Paracarophenax alternatus Xu and Zhang sp. nov. is most similar to P. scolyti Khaustov, 1999 in having two pairs of setae on tergite EF; lacking setae ag; and trochanters I–II with a seta (v′ present); tracheae with atrium terminating in brush-like extensions; but mainly differs in the following characters: setae f about twice as long as e (setae e slightly longer than f in P. scolyti); setae v₂, c₁ and f subequal in length, sc₂, c₂ and d subequal in length, and about four-fifths as long as seta f (setae v₂, sc₂, d and e subequal in length, c₁, c₂ and f subequal in length in P. scolyti); setae h₂ located proximate to h₁, about one fifth of the distance between setae e and f (the distance between setae h₂ and h₁ equal to the distance between setae e and f in P. scolyti); femora I–IV with 3, 3, 2, 0 setae (femora I–IV with 3, 3, 1, 0 setae in P. scolyti); setae v′ on genu II spine-like (setae v′ on genu II setiform in P. scolyti); on tibia II, setae v′ longer than l′ (setae l′ about twice as long as setae v′ in P. scolyti).

FIGURE 5.

Habitus photographs of ventral view of adult Monochamus alternatus with females Paracarophenax alternatus Xu and Zhang sp. nov. attached around the coxal cavity.

FIGURE 6.

Photograph of Paracarophenax alternatus Xu and Zhang sp. nov. when feeding on the egg of Monochamus alternatus.