Redescription of Bryobia pritchardi Rimando, 1962 (Acari: Tetranychidae), with an ontogeny of chaetotaxy

Bryobia pritchardi Rimando 1962, collected from Drymaria cordata in the Hainan province of China, is redescribed with a detailed illustration and description of all life stages. Special attention is given to ontogenetic changes, especially in leg setae, as well as intraspecific variation and asymmetry of these setae.


Introduction
The subfamily Bryobiinae usually identified by their plesiotypic features, such as: the empodium bearing tenent hairs; the lack of silk production; the position of the duplex setae at the apex of the tarsus; declivate tip of the tarsus; three pairs of pseudanal setae usually present; and four pairs of propodosomal setae often present (Lindquist 1985). Numerous Bryobiinae taxa add more whorls of leg setae during ontogeny, a feature seen in no other Tetranychoidea (Lindquist 1985).
Bryobia is placed within the tribe Bryobiine, which is defined by its uncinate claws. The genus Bryobia is the largest genus of Bryobiinae and contains several species of significant economic importance in many parts of world (Hatzinikolis & Emmanouel 1991), it is distinctive by the following features: (1) Four pairs of propodosomal setae present, the anterior two pairs of which (v1, v2) are usually located on prominent projections over the gnathosoma; (2) the usual 12 pairs of dorsal hysterosomal setae; and (3) empodia II-IV with more than one pair of tenent hairs (Gonzalez 1977).
A total of 137 species of Bryobia are described, 19 of them from China (Migeon & Dorkeld 2006Hong et al. 2010;Hu & Chen 1993;He & Tan 1993;Wang & Cui 1991;Wang 1985Wang , 1981Wang & Zhang 1984;Ma & Yuan 1984, 1981, 1980. Beyond these descriptions, knowledge of the Bryobia mite fauna in China is relatively poor, but Bryobia pritchardi Rimando 1962 is common nationwide and in the east-Asian region. Bryobia pritchardi, was erected by Rimando in 1962 from Paederia foetida (Rubiaceae) in the Philippines; Ehara (1969) and Tseng (1990) collected it in Taiwan, from Paederia scandens; Wang (1981) and Ma et al. (1984) reported it from Hainan Island, China, collected from P. foetida (as P. scandens, a junior synonym) and Acalypha hainanensis (Euphorbiaceae); Ehara (1999) reported it in Japan (Shikoku and Kyushu islands) from P. scandens and Cucumis melo (Cucurbitaceae). Bryobia pritchardi is redescribed herein based on all immature stages collected from Drymaria cordata (Caryophyllaceae) in Hainan province, China. We also examined the type specimens of B. pritchardi, in order to compare the types and our specimens.
Recently great importance has been attached to understanding the patterns of setal additions throughout ontogenetic development of the Tetranychoidea (Khanjani et al. 2018;Seeman et al. 2017;Li et al. 2018Li et al. , 2017Xu et al. 2017;Yi et al. 2017Yi et al. , 2013De Castro et al. 2015;Beard & Ochoa 2010;Beard & Walter 2010). There are few scholars who have payed attention to the ontogenetic patterns for species of Bryobia. Immature stages for some other species have been described, such as Auger & Migeon (2014), who noted the development of the prodorsal lobes during ontogeny and also provided leg setal counts. However, since the important work of Lindquist (1985), authors have provided full characteristic notations for a Bryobia sp. Until the important task of comparative homologization of leg setae is accomplished for the families of Tetranychoidea as a group, a great deal of data of potential importance to the systematics and classification of these groups will remain masked. We herein examine setal variations of female leg I based on 25 specimens, and also discuss other intraspecific morphological variation.

Material and methods
The mite specimens were mounted in Hoyer's medium on slides and examined using a Nikon DS-Ri2 microscope with differential interference contrast. Line drawings were prepared with the aid of a drawing tube attached to the microscope. All measurements were taken with the software Leica Application Suite V 4.4 and are given in micrometers (μm). Setae were measured from the centre of the setal base to the tip of the seta; distances between setae were measured from the centre of one setal base to that of another. Legs were measured from the base of the trochanter to the distal end of tarsus (excluding pretarsus). Terminology follows that of Lindquist (1985).

Leg
Co Tr Fe Ge Ti Ta      (d, v′-v″, l′-l″, bv″, bv′1, bl′1-bl″1) are shown with the frames; the remaining setae always vary in position and number. bases ( Figure 25B). Additionally, they share similar prodorsal lobes, which are well-developed, the inner lobes sharing a more or less triangular broad base, and are well separated distally with an obvious incision ( Figure 25E).
Bryobia pritchardi is most similar to B. praetiosa Koch, 1836, with both species characterized by: the shape of the dorsal setae; having strong anterior propodosomal projections; and empodia II-IV about as long as the claw, with two rows of ventrally directed tenent hairs. B. pritchardi is diagnosed by empodia I, which bears two rows of three ventrally directed tenent hairs, and true claws I have 3 pairs of tenant hairs. In B. praetiosa, empodia I has only a single pair of tenent hairs, and true claw I is pad-like and has more than three pairs of tenant hairs (Pritchard & Baker 1955;Ehara 1956).
We also note the recent work of Fashing (2016), who demonstrated that the prodorsal lobes, a critical feature for species and even genus level differentiation, is prone to intraspecific variation. However, here we found no variation within our populations, but we do draw attention to the differences between life stages and sexes (Fig. 5).

Ontogenetic development of podosoma
The ontogenetic changes of B. pritchardi are listed in Table 1.
The setation and ontogeny of idiosomal setae is typical for the Bryobiinae (Lindquist 1985). All dorsal setae and pseudanal setae are present throughout all stages. Ventral setae (1c, 2c and 3b) are added in the protonymph, 2b, 4a and 4b are added in the deutonymph. Aggenital setae ag are added in the protonymph; the first pair of genital setae g1 are added in the deutonymph. The second pair g2 are added in the adults, with males grouping their genital setae closely as a series of five pairs on the genitoanal valves (Lindquist 1985;Figs. 27A-B).

Ontogenetic development of leg setae
Leg I: Compared with the basic pattern described by Lindquist (1985), there are variations of leg setae found on the tarsus and femur, while almost no variation was found on the tibia, genu and trochanter.
Leg II: The setae basically show the basic pattern as described by Lindquist (1985) from larva to deutonymph, but there are variable changes in adult females of B. pritchardi (Tables 2,  3).
Leg IV: The complement of setae of two species from larva to deutonymph is less variable. The number of protonymphal setae in this species from tarsus to trochanters are 6-5-2-2-0, showing the basic pattern, as does the deutonymph (10-5-2-2-1), except that setae d suppressed on the genua. On adult females, setae l″ (instead of v″) are present on the genua, and l′ (instead of v″) are present on femora.