The genus Oligonychus Berlese (Acari, Prostigmata, Tetranychidae): taxonomic assessment and a key to subgenera, species groups, and subgroups

Hafiz Muhammad Saqib Mushtaq; Fahad Jaber Alatawi; Muhammad Kamran; Carlos Holger Wenzel Flechtmann

doi:10.3897/zookeys.1079.75175

Research Article

The genus Oligonychus Berlese (Acari, Prostigmata, Tetranychidae): taxonomic assessment and a key to subgenera, species groups, and subgroups

Hafiz Muhammad Saqib Mushtaq^‡, Fahad Jaber Alatawi^‡, Muhammad Kamran^‡, Carlos Holger Wenzel Flechtmann^§

‡ King Saud University, Riyadh, Saudi Arabia

§ Universidade de São Paulo, São Paulo, Brazil

Corresponding author: Fahad Jaber Alatawi ( falatawi@ksu.edu.sa )

Academic editor: Xiao-Feng Xue

This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Citation: Mushtaq HMS, Alatawi FJ, Kamran M, Flechtmann CHW (2021) The genus Oligonychus Berlese (Acari, Prostigmata, Tetranychidae): taxonomic assessment and a key to subgenera, species groups, and subgroups. ZooKeys 1079: 89-127. https://doi.org/10.3897/zookeys.1079.75175

ZooBank: urn:lsid:zoobank.org:pub:E3D873CB-7039-478D-8986-08E461087E98

Abstract

A comprehensive taxonomic assessment of the most agriculturally important and highly diverse spider mite genus, Oligonychus Berlese (Acari: Tetranychidae) was performed. The sub-generic division, species groups, doubtful species, species complexes and the interpretation of a key generic character are discussed. Based on the orientation of the male aedeagus, only two subgenera, namely Oligonychus Berlese (aedeagus downturned) and Reckiella Tuttle & Baker (aedeagus upturned), are valid in the genus Oligonychus. The subgenera Homonychus Wainstein, Metatetranychoides Wainstein, and Wainsteiniella Tuttle & Baker are considered to be synonyms of the subgenus Oligonychus, whereas the subgenus Pritchardinychus Wainstein is proposed as a synonym of the subgenus Reckiella. Moreover, based on female morphological characters, four species groups (coffeae, exsiccator, iseilemae, and peruvianus) and 11 species subgroups (aceris, biharensis, coffeae, comptus, exsiccator, gossypii, iseilemae, peruvianus, pritchardi, smithi, and subnudus) are suggested in the subgenera Oligonychus and Reckiella. Fourteen Oligonychus species are proposed as species inquirendae, and potential cryptic species complexes in the genus Oligonychus are briefly highlighted. It is agreed that the clunal seta h₁ is always absent, while the para-anal setae h₂ and h₃ are always present in the genus Oligonychus. A key to subgenera, species groups, and species subgroups of the genus Oligonychus is provided.

Keywords

Morphology, species complex, species identification, species inquirenda, spider mite, taxonomy

Introduction

Oligonychus Berlese (Acari: Prostigmata: Tetranychidae) is the largest genus of the spider mites, comprising > 200 species, and its members have been reported throughout the world (Migeon and Dorkeld 2021). A range of feeding specificity occurs throughout the genus, with polyphagous, oligophagous and monophagous species present on both broad and narrow leaved commercial (fruits, agronomic crops, etc.) and non-commercial (wild trees, shrubs, grasses, etc.) host plants (Pritchard and Baker 1955; Jeppson et al. 1975; Beard et al. 2003; Matsuda et al. 2012; Migeon and Dorkeld 2021). Some economically significant species, e.g., the date palm mite O. afrasiaticus (McGregor), the tea red spider mite O. coffeae (Neitner), the banks grass mite/new world date mite O. pratensis (Banks), and the avocado brown mite O. punicae (Hirst), have been spread across the world and are now widely distributed (Jeppson et al. 1975; Migeon and Dorkeld 2021).

The authenticity of sub-generic division of the genus Oligonychus (Wainstein 1960; Tuttle and Baker 1968) always remains questionable, due to the use of inconsistent characters, e.g., striae pattern on dorsal opisthosoma and number of tactile setae on tibia I (Meyer 1974, 1987; Bolland et al. 1998; Beard et al. 2003, 2008; Khanjani et al. 2018; Li et al. 2018, 2019). So, to confirm the current taxonomic status of the six subgenera of Oligonychus suggested by Tuttle and Baker (1968), a comprehensive morphological investigation based on all known Oligonychus species is needed.

The species identity in the genus Oligonychus is usually challenging due to the limited number of potential diagnostic characters, presence of intraspecific variation, minute differences in male aedeagus morphology and interspecific similarities in females (Pritchard and Baker 1955; Meyer 1974, 1987; Jeppson et al. 1975; Li et al. 2018). Mostly, Oligonychus species have been differentiated based only on the aedeagus morphology (Pritchard and Baker 1955; Meyer 1974, 1987). In addition, specimens of both sexes are frequently required for precise identification of Oligonychus species (Ben-David 2008; Meyer 1987). The aedeagal traits could be unreliable and confusing when male specimens were not mounted in a precisely lateral position, and in some cases the aedeagus was neither described nor illustrated (e.g., O. mangiferus Rahman & Sapra, 1940). Also, intraspecific variations in aedeagus shape or variation in the interpretation of aedeagus shape that can manifest as intraspecific variation, have been observed in species described from various geographical localities (e.g., O. pratensis; McGregor 1939; Pritchard and Baker 1955; Meyer 1959, 1974, 1987; Baker and Pritchard 1962; Estebanes and Baker 1968; Jeppson et al. 1975; Tuttle et al. 1976; Baker and Tuttle 1994). Furthermore, aedeagus shape may appear variable at different levels of focus under the microscope (e.g., O. ephamnus Beard & Walter, 2003). There are 17 Oligonychus species that have been described based only on females with the males remaining unknown, e.g., O. mactus Tseng and O. nielseni Reeves (Reeves 1963; Tseng 1990), and a few species that were inadequately described, e.g., O. kobachidzei (Reck) and O. stenoperitrematus (Ugarov and Nikolskii), with important morphological information of male/female not included (Ugarov and Nikolskii 1937; Reck 1947). Some species, e.g., O. caucasicus (Reck) and O. daleae Tuttle, Baker & Abbatiello, were reported as new to science, without making any remarks regarding related or similar species (Reck 1956; Tuttle et al. 1976). This lack in clarity has resulted in the suggested existence of several species complexes within the genus Oligonychus e.g., coffeae complex and pratensis complex (Pritchard and Baker 1955; Meyer 1987; Ehara and Gotoh 2007; Lara et al. 2017; Khanjani et al. 2018; Li et al. 2018). Consequently, there is a great need for developing an integrative taxonomic approach to clarify the actual status of many closely related Oligonychus species and for establishing truly diagnostic characters for accurate and consistent species separation.

The presence of two pairs of para-anal setae (h₂ and h₃) is one of the important distinguishing character of Oligonychus (Lindquist 1985; Beard et al. 2003, 2008; Seeman and Beard 2011; Arabuli and Gotoh 2018; Khanjani et al. 2018; Li et al. 2019). However, there are contradictions found among different taxonomists even when it comes to identifying the h₂ setae in Oligonychus species (Pritchard and Baker 1952, 1955; Meyer 1974, 1987; Jeppson et al. 1975; Lindquist 1985; Bolland et al. 1998; Knihinicki and Flechtmann 1999; Flechtmann and Etienne 2006; Beard et al. 2008; Arabuli and Gotoh 2018; Khanjani et al. 2018; Li et al. 2019).

Keeping in view the importance of taxonomic adversities in the genus Oligoncyhus, the objectives of the present study were to i) assess the current taxonomic status of the sub-generic division of Oligonychus, ii) classify all species of Oligonychus into species groups and subgroups based on consistent morphological characters, iii) construct a diagnostic key to subgenera, groups and subgroups of Oligonychus, and iv) highlight or discuss the doubtful species, species complexes and contradiction/confusion in the identification of para-anal setae in Oligonychus.

Materials and methods

The taxonomic literature of 211 Oligonychus species was critically reviewed to confirm the current status of subgeneric division and doubtful and closely related Oligonychus species, create species groups, and prepare a key for their identification; in addition to discussing the confusion/contradiction associated with the naming of para-anal setae. To verify the consistency in expression of some female morphological characters and their significance in creating species groups and subgroups within the genus Oligonychus, numerous spider mite samples were collected and observed from Egypt, Mexico, Pakistan, Saudi Arabia, USA, and Yemen. In addition, mite samples of some other closely or distantly related Tetranychini genera viz. Tetranychus Dufour, Eotetranychus Oudemans, Mixonychus Meyer & Ryke, Neotetranychus Trägårdh, Sonotetranychus Tuttle et al., and Schizotetranychus Trägårdh, were collected from various localities in different regions of Saudi Arabia, to confirm the absence/presence and shape and position of the clunal (h₁) and para-anal setae (h₂ and h₃). The nomenclature of Grandjean (1939, 1944a, 1944b, 1947) was followed for body setae, and Lindquist (1985) for leg chaetotaxy and other terminologies.

Results and discussion

Family Tetranychidae Donnadieu

Subfamily Tetranychinae Berlese

Tribe Tetranychini Reck

Genus Oligonychus Berlese, 1886.

Oligonychus Berlese, 1886: 24, Pritchard and Baker 1955: 270, Wainstein 1960: 203, Tuttle and Baker 1968: 116, Meyer 1974: 248, Mitrofanov 1977: 1801–1802, Meyer 1987: 142, Beard et al. 2003: 51–78, Khanjani et al. 2018: 223–287, Li et al. 2019: 1071–1106.

Type species

Heteronychus brevipodus Targioni-Tozzetti, 1878: 255.

Diagnosis

(Based on: Pritchard and Baker 1955; Tuttle and Baker 1968; Meyer 1974, 1987; Beard et al. 2003, 2008; Khanjani et al. 2018). Empodia well developed, claw-like with proximoventral hairs (except male leg I with hairs modified into spur) that are as long as or shorter than empodial claw on most of legs; two pairs of duplex setae on tarsus I, distal and adjacent; opisthosoma with 11 pairs of dorsal setae (c_1-3, d_1-2, e_1-2, f_1-2, h_2-3; n.b. setae h₂ and h₃ usually inserted ventrally); clunal setae h₁ always absent.

Taxonomic review of the genus Oligonychus

The genus Oligonychus was erected by Berlese (1886), based on Heteronychus brevipodus Targioni-Tozzetti as the type species (specimen was a nymph), reported from the Holly Oak (Quercus ilex L., Fagaceae) in Italy (Targioni-Tozzetti 1878). Because Berlese (1886) did not clearly describe the presence of proximoventral hairs on the empodial claws in the diagnosis of Oligonychus, Zacher (1913) created a new genus, Paratetranychus, and described the presence of proximoventral hairs in it. McGregor (1950) followed the work of Zacher (1913) by giving priority to Paratetranychus over Oligonychus, and placed all Oligonychus species within Paratetranychus. Five years later, Pritchard and Baker (1955) redefined the genus Oligonychus, and synonymized the genera Paratetranychus and Tacebia (Yokoyama 1929) with Oligonychus.

Subdivision of the genus Oligonychus

The genus Oligonychus has a history of subdivision into species groups (Pritchard and Baker 1955; Ehara 1999) and subgenera (Wainstein 1960; Tuttle and Baker 1968). Initially, Pritchard and Baker (1955) divided Oligonychus species into five species groups viz. ununguis, peruvianus, pritchardi, pratensis, and mcgregori. The ununguis group was further divided into five species subgroups viz. aceris, bicolor, boudreauxi, subnudus, and ununguis. This grouping was based on both male and female morphological characters, including the shape or orientation of the male aedeagus, number of tactile setae on tibia I, number of tactile setae on tarsus I proximal to the proximal duplex setae and ventrally near or beyond the duplex setae, number of proximoventral hairs on the empodium, the pattern of striation on the female dorsal opisthosoma, shape of dorsal body setae, and the shape of the peritreme (Pritchard and Baker 1955). Another species group, the clavatus species group, was subsequently created by Ehara (1999) based on the number of tactile setae on tibia I, aedeagal morphology and female body color, and included O. clavatus (Ehara) and O. pustulosus Ehara.

Wainstein (1960) proposed five sub-genera of Oligonychus, namely Oligonychus Berlese, Homonychus Wainstein, Metatetranychoides Wainstein, Pritchardinychus Wainstein, and Paratetranychus Zacher. This sub-generic division was based on both male and female morphological characters, including the length of dorsal body setae, dorsal setae set on tubercles or not, the total number of setae on each of female tibia I, tibia II and tarsus I, and the morphology of the male aedeagus. Three of these sub-genera were further categorized into species groups based on the chaetotaxy of legs I and II. The subgenus Oligonychus was divided into three species groups: boudreauxellus, bakerellus, and berlesellus; the subgenus Paratetranychus was divided into two groups: ununguellus and zacherellus; and the subgenus Pritchardinychus was divided into three groups: pritchardellus, pratensellus, and mcgregorellus. Later, Tuttle and Baker (1968) synonymized the subgenus Paratetranychus with the subgenus Oligonychus, and retained four of the sub-genera created by Wainstein (1960). Tuttle and Baker (1968) then created two more sub-genera, namely Wainsteiniella Tuttle & Baker and Reckiella Tuttle & Baker. This sub-generic division was again based on both male and female characters, including the pattern of the striation of the female dorsal opisthosoma, shape and orientation of male aedeagus, length of dorsal body setae, and total number of tactile setae on tibia I. Tuttle and Baker (1968) relied heavily on one of the female morphological characters to differentiate these six subgenera, the pattern of the striae on the dorsal opisthosoma. Mitrofanov (1977) also used this character to raise the sub-genera Metatetranychoides, Pritchardinychus, and Homonychus to genus level, and to erect a new genus, Neonychus, with O. licinus Baker & Pritchard as type species. Meyer (1987) found that the pattern of dorsal striae on the female opisthosoma to be a variable character, and disagreed with the subgeneric divisions of Oligonychus made by Wainstein (1960) and Tuttle and Baker (1968). The sub-genera are not always well distinguished and several morphological characters, such as the pattern of striae between dorsal setal pairs e₁ and f₁ on the female and the number of tactile setae on tibia I, have been found to be variable (Meyer 1987). Such variable characters cannot be used to reliably separate the subgenera of Oligonychus (Meyer 1987; Beard et al. 2003, 2008; Li et al. 2018). These sub-divisions were made for practical rather than phylogenetic reasons, and have resulted in a somewhat artificial classification (Helle et al. 1981; Meyer 1987).

Bolland et al. (1998) supported homogeneity within only the two sub-genera viz. Reckiella and Oligonychus, based on biological, morphological, and molecular data, but felt that the homogeneity of the remaining four sub-genera (Homonychus, Metatetranychoides, Pritchardinychus, and Wainsteiniella) requires further investigation to confirm their validity. Additionally, molecular investigations have revealed the presence of “polyphyly” in the genus Oligonychus (Navajas et al. 1996; Ben-David et al. 2007; Matsuda et al. 2014).

Species complexes in the genus Oligonychus

Several species complexes within the genus Oligonychus have been suggested by various authors in the past, for example a coffeae complex, pratensis complex, perseae complex, subnudus complex, sacchari complex, and ununguis complex (Pritchard and Baker 1955; Cromroy 1958; Meyer 1987; Ehara and Gotoh 2007; Lara et al. 2017; Li et al. 2018), and these are difficult to resolve based on morphology (Pritchard and Baker 1955). The coffeae complex sensu Ehara & Gotoh comprises four morphologically similar species, namely O. coffeae, O. gotohi Ehara, O. castaneae Ehara & Gotoh, and O. amiensis Ehara & Gotoh (Ehara and Gotoh 2007). Originally, the Japanese population of O. gotohi was considered to represent a single species, however, genetic crossing studies revealed that this population is a complex of three reproductively isolated species (O. gotohi, O. castaneae, and O. amiensis) (Ehara and Gotoh 2007; Gotoh et al. 2007). Moreover, some variation in morphological characters, e.g., aedeagus shape and number of tactile setae on tarsus II, have been observed in various taxa identified as O. coffeae reported from different geographical localities (Pritchard and Baker 1955; Baker and Pritchard 1960; Ehara 1969, 1999; Meyer 1974, 1987; Wang 1981), highlighting the possibility that further cryptic species could be separated within this complex (Ehara and Gotoh 2007).

The pratensis complex sensu Pritchard & Baker has been recognized by various authors based on observed variations or differences in some morphological characters among different populations identified as O. pratensis, e.g., aedeagus shape and striae pattern on dorsal hysterosoma (Pritchard and Baker 1955; Meyer 1974; Li et al. 2018). A subnudus complex was suggested by Pritchard and Baker (1955), when morphological variations in shape/length of some hysterosomal setae and the stylophore were observed between two populations of O. subnudus (McGregor) from two different localities in the United States.

Based on the variations in descriptions and illustrations of two morphologically similar Oligonychus species, O. sacchari (McGregor) and O. saccharinus Baker & Pritchard (McGregor 1950; Pritchard and Baker 1955; Baker and Pritchard 1960; Meyer 1974), the sacchari complex was proposed by Khanjani et al. (2018). Although, Meyer (1974) comprehensively discussed the morphological differences between these two closely related species, their taxonomic identities remain doubtful, and require further investigations through the combined use of morphological and molecular data (Khanjani et al. 2018).

The possibility of an ununguis complex was suggested by Pritchard and Baker (1955) to include O. coniferarum (McGregor), O. mangiferus, O. peronis Pritchard & Baker, O. punicae, and O. ununguis (Jacobi). The taxonomic identities of most species in the ununguis complex remain questionable, and the females are indistinguishable. The minute differences in the shape of the aedeagus and the size of female palp spinneret are often used for differentiating these closely related species (Pritchard and Baker 1955; Meyer 1987; Khanjani et al. 2018). However, some of these species e.g., O. mangiferus, O. punicae, and O. vitis, are very close morphologically, can be exceedingly difficult to differentiate as separate species, and are part of the “greatest taxonomic problem” in the genus Oligonychus (Meyer 1987; Khanjani et al. 2018).

Para-anal setae in the genus Oligonychus

In many genera of the tribe Tetranychini Reck, three pairs of h setae (h₁, h₂, and h₃) are consistently present on the fifth segment (H) of opisthosoma (Pritchard and Baker 1955; Lindquist 1985; Bolland et al. 1998). However, one of these setae (h₁ or the clunals) is absent in some Tetranychini genera, e.g., Oligonychus and Tetranychus (Pritchard and Baker 1955; Lindquist 1985; Bolland et al. 1998; Seeman and Beard 2011; Alatawi and Kamran 2018; Khanjani et al. 2018). Earlier, Pritchard and Baker (1955) believed that seta h₁ (clunal seta) is consistently present and h₂ (one of a pair of para-anal setae displaced terminally to become a post anal seta) is absent in Oligonychus. Later, Lindquist (1985) analyzed and discussed the relative position and shape of the para-anal setae (h₂ and h₃) with respect to setal homologies and concluded that the clunal seta h₁ is apparently absent in Oligonychus, whereas seta h₂ is consistently present (Lindquist 1985), as previously explained by many authors (Oudemans 1930; Pritchard and Baker 1952; Attiah 1970). According to Lindquist (1985) and Seeman and Beard (2011), para-anal setae h₂ and h₃, are consistently present in Oligonychus. Confusion is generated when simple positions are used to name setae rather than homologies. Lindquist (1985) and Seeman and Beard (2011) use homologies and state that “two pairs of para-anal setae h₂ and h₃, are consistently present in Oligonychus and related genera”. Many authors have followed the work of Lindquist (1985), and also consider setae h₁ to be absent, and h₂ and h₃ to be present in Oligonychus (Beard et al. 2003, 2008; Kamayev 2017; Li et al. 2017, 2018, 2019; Arabuli and Gotoh 2018; Khanjani et al. 2018). Pritchard and Baker (1952) originally assumed that seta h₁ (clunal) was present or absent, with two pairs of para-anal setae present; however, Prtichard and Baker (1955) altered this view and assumed the clunal setae to always be present. They stated that there are two pairs of para-anal setae, and that the posterior pair get displaced terminally to become a post-anal seta, and that it is this seta that is absent in two genera (Oligonychus and Tetranychus). Meyer (1987) and Bolland et al. (1998) also use a positional approach to naming setae and assume the clunals to be consistently present, but interpret setae h₂ or h₃ as absent in Oligonychus and Tetranychus. Thus the setae are named as one pair of clunals and two pair of para-anals, and as a consequence, the statement “one pair of para-anal setae is present in Oligonychus and related genera” appears to be contradictory to what other authors believe. Many authors also mention the presence of h₁ and only one pair of para-anal setae (either h₂ or h₃) in the genus diagnosis and descriptions/illustrations of different Oligonychus species (Rimando 1962; Tuttle and Baker 1968; Chaudhri et al. 1974; Meyer 1974; Jeppson et al. 1975; Tuttle et al. 1976; Zaher et al. 1982; Tseng 1990; Gupta and Gupta 1994; Smiley and Baker 1995; Ehara 1999; Knihinicki and Flechtmann 1999; Flechtmann and Etienne 2006; Ehara and Gotoh 2007; Zeity 2015, 2016; Alatawi and Kamran 2018).

Subgeneric division of the genus Oligonychus

Subgenus Oligonychus Berlese

Type species. Heteronychus brevipodus Targioni-Tozzetti, 1878: 255.

Diagnosis (based on male). Male aedeagus with shaft bending ventrad, downturned part mostly tapering distally, forming an acute or blunt tip.

Subgenus Reckiella Tuttle & Baker

Type species. Tetranychus pratensis Banks, 1912: 97.

Diagnosis (based on male). Male aedeagus with shaft bending dorsad, or shaft initially bends dorsad then distal part turned ventrad, upturned part usually without tapering end, distally forming knob, sigmoidal shape and blunt or rounded tip.

Only two subgenera are hereby recognized: Oligonychus Berlese and Reckiella Tuttle & Baker, instead of five and six subgenera as proposed by Wainstein (1960) and Tuttle and Baker (1968), respectively. The subgenera Homonychus, Metatetranychoides and Wainsteiniella are considered to be synonyms of the subgenus Oligonychus, and subgenus Pritchardinychus is recommended as a synonym of the subgenus Reckiella. In total, 76 species are placed in the subgenus Oligonychus, whereas 118 Oligonychus species are designated to the subgenus Reckiella. However, approximately 17 Oligonychus species could not be assigned to any of the two subgenera, because their descriptions were based only on females, with males remaining unknown in the original and subsequent descriptions.

In the present study, we suggest using the male aedeagus shape and its orientation as a consistent and strong morphological character to redefine the two valid Oligonychus subgenera, instead of using inconsistent or variable characters, e.g., striation pattern on dorsal hysterosoma and number of tactile setae on tibia I (Wainstein 1960; Tuttle and Baker 1968; Meyer 1987). The proposed suggestion also agreed well with the molecular separation of various Oligonychus species into two groups, which successfully coincided with their morphological grouping based on male aedeagus i.e., aedeagus upturned vs. aedeagus downturned (Ben-David et al. 2007; Matsuda et al. 2012; Unpublished results). This study also supported the findings of Meyer (1974, 1987), who was the first to disagree with the subgeneric divisions of Oligonychus (Wainstein 1960; Tuttle and Baker 1968), due to the inconsistency of diagnostic characters, e.g., striation pattern on dorsal opisthosoma and number of tactile setae on tibia I. Meyer (1987) found that some of the African Oligonychus species, e.g., O. andrei Gutierrez and O. pennisetum, would not fit in any of the six Oligonychus subgenera (Tuttle and Baker 1968). Subsequently, more authors disagreed with the six-subgeneric Oligonychus system (Flechtmann and Alves 1976; Helle et al. 1981; Bolland et al. 1998; Beard et al. 2003, 2008; Khanjani et al. 2018; Li et al. 2018). However, there are still authors who continue using the Oligonychus six-subgeneric system (Kamayev 2017; Li et al. 2019), without confirming the validity of characters that were initially devised to erect these subgenera (Tuttle and Baker 1968).

Based on the upturned aedeagus and tibia I with nine tactile setae (Tuttle and Baker 1968; Jeppson et al. 1975), we here synonymize the subgenus Pritchardinychus with the subgenus Reckiella. Both of these subgenera were previously separated using an inconsistent character of regarding the dorsal hysterosomal striae on the female (Meyer 1987) – longitudinal striae only between setae f₁-f₁ in Reckiella or transverse striae on entire hysterosoma in Pritchardinychus (Tuttle and Baker 1968). In the present study, we observed longitudinal, irregular longitudinal or oblique striae present between both e₁-e₁ and f₁-f₁ setae in 10 Oligonychus species of the valid subgenus Reckiella, and longitudinal striae between only e₁-e₁ setae in a species (O. andrei Gutierrez) of Reckiella (Zacher 1921; Baker and Pritchard 1960; Rimando 1962; Meyer 1964, 1965, 1974, 1987; Ehara 1966; Gutierrez 1966, 1967; Lo and Ho 1989; Tseng 1990). Furthermore, 13 Oligonychus species of the valid subgenus Reckiella with upturned aedeagus have seven or less than seven tactile setae on tibia I rather than nine setae. Also, the pattern of opisthosomal/hysterosomal striae of some of these 13 species varies, e.g., reticulated pattern of irregular elongate elements in the case of O. comptus Meyer & Bolland, whole hysterosoma with transverse striae in the case of O. anonae Paschoal, O. beeri Estebanes & Baker, O. chiapensis Estebanes & Baker and O. iseilemae (Hirst), transverse except V-shaped/irregular pattern between e₁-e₁ setae in O. megandrosoma Flechtmann & Alves, and transverse except slightly U-shaped pattern between e₁-f₁ area in O. poutericola Feres & Flechtmann (Hirst 1924; Baker and Pritchard 1962; Estebanes and Baker 1968; Livshits 1968; Gutierrez 1969; Paschoal 1970; Meyer 1974, 1987; Flechtmann and Alves 1976; Meyer and Bolland 1984; Feres and Flechtmann 1986; Mendonca et al. 2010).

We also synonymized the subgenera that have a downturned aedeagus, i.e., Homonychus, Metatetranychoides, and Wainsteiniella (Tuttle and Baker 1968; Jeppson et al. 1975), with the subgenus Oligonychus. Previously, these four subgenera were also diagnosed and separated based mainly on the inconsistent character of dorsal hysterosomal striae of the female (Meyer 1987), with Oligonychus and Wainsteiniella having entirely transverse striae, and Homonychus with longitudinal and Metatetranychoides with irregular striae between only setae e₁-e₁ (Tuttle and Baker 1968; Jeppson et al. 1975). Of the four subgenera, Wainsteiniella was further diagnosed with shorter dorsal body setae (Tuttle and Baker 1968). However, we observed that some Oligonychus (Oligonychus) species, or populations of a species, have short dorsal setae with V-shaped, longitudinal, irregular, or oblique striae between d₁-e₁ setal area instead of entirely transverse, e.g., O. hondoensis (Ehara)) and O. plumosus Estebanes & Baker (Pritchard and Baker 1955; Tuttle et al. 1976). In addition, the subgenus Oligonychus was also differentiated by having seven tactile setae on tibia I (Tuttle and Baker 1968), and we found some species with more than seven, e.g., O. bambusae Karuppuchamy & Mohanasundaram and O. smithi Cromroy, or fewer than than seven, e.g., O. alpinus (McGregor). Moreover, O. bambusae possesses longitudinal striae between setae f₁-f₁ (McGregor 1936; Cromroy 1958; Karuppuchamy and Mohanasundaram 1988; Baker and Tuttle 1994).

Subdivision of Oligonychus species into groups and subgroups

In the present study, four species groups and 11 species subgroups are recognized under the valid subgenera of Oligonychus and Reckiella, based on the combination of three morphological characters of the adult female: the number of tactile setae on tibiae I and II, the length of dorsal hysterosomal setae c₁, and the pattern of striae on the dorsal hysterosoma. These characters were previously used to erect species groups by Pritchard and Baker (1955) and subgenera by Tuttle and Baker (1968) in Oligonychus.

Species groups and subgroups in the subgenus Oligonychus

The Oligonychus (Oligonychus) is subdivided into two species groups, the peruvianus species group (Pritchard and Baker 1955) and the newly proposed coffeae species group. The peruvianus species group is further categorized into two newly proposed species subgroups, the smithi species subgroup and the peruvianus species subgroup; whereas the coffeae species group is categorized into three species subgroups, subnudus species subgroup (Pritchard and Baker 1955), aceris species subgroup (Pritchard and Baker 1955), and the newly proposed coffeae species subgroup.

The following four species of the subgenus Oligonychus could not be assigned to any species group/subgroup, because they were briefly described and certain key characters of the female were not included:

O. brevipilosus (Zacher, 1932)

O. kobachidzei (Reck, 1947)

O. meifengensis Lo & Ho, 1989

O. nuptialis (Zacher, 1932)

peruvianus species group (sensu Pritchard & Baker, 1955)

Exemplar species. Tetranychus peruvianus McGregor, 1917: 581.

Diagnosis (based on female). More than seven (eight or nine) tactile setae on tibia I.

smithi new species subgroup

Exemplar species. Oligonychus smithi Cromroy, 1958: 61.

Diagnosis (based on female). More than seven (eight or nine) tactile setae on tibia I, and dorsal hysterosomal setae c₁ long, reaching well beyond bases of setae d₁. This subgroup comprises two species:

O. bambusae Karuppuchamy & Mohanasundaram, 1988

O. smithi Cromroy, 1958

peruvianus new species subgroup

Exemplar species. Tetranychus peruvianus McGregor, 1917: 581.

Diagnosis (based on female). More than seven (eight or nine) tactile setae on tibia I, and dorsal hysterosomal setae c₁ short (almost one-half to three-fourths as long as the distance between c₁-d₁), not reaching bases of setae d₁. This subgroup includes three species:

O. peruvianus (McGregor, 1917)

O. perseae Tuttle, Baker & Abbatiello, 1976

O. sumatranus Ehara, 2004

coffeae new species group

Exemplar species. Acarus coffeae Nietner, 1861: 31.

Diagnosis (based on female). Seven or less than seven (five or six) tactile setae on tibia I.

subnudus species subgroup (sensu Pritchard and Baker 1955)

Exemplar species. Paratetranychus subnudus McGregor, 1950: 354

Diagnosis (based on female). Seven or less than seven (five or six) tactile setae on tibia I, and dorsal hysterosomal setae c₁ short (almost one half to three-fourths as long as the distance between c₁-d₁), not reaching bases of setae d₁. This subgroup includes 18 species:

O. baipisongis Ma & Yuan, 1976

O. boudreauxi Pritchard & Baker, 1955

O. clavatus (Ehara, 1959)

O. cunliffei Pritchard & Baker, 1955

O. hondoensis (Ehara, 1954)

O. karamatus (Ehara, 1956)

O. livschitzi Mitrofanov & Bossenko, 1975

O. laricis Reeves, 1963

O. milleri (McGregor, 1950)

O. pinaceus Mitrofanov & Bossenko, 1975

O. pini Tuttle, Baker & Abbatiello, 1976

O. pityinus Pritchard & Baker, 1955

O. plumosus Estebanes & Baker, 1968

O. subnudus (McGregor, 1950)

O. tuberculatus Estebanes & Baker, 1968

O. verduzcoi Estebanes & Baker, 1968*

O. yasumatsui Ehara & Wongsiri, 1975

O. yuae Tseng, 1975

aceris species subgroup (sensu Pritchard and Baker 1955)

Exemplar species. Acarus aceris Shimer, 1869: 320

Diagnosis (based on female). Five or six tactile setae on tibia I, and dorsal hysterosomal setae c₁ long, reaching to (sub-equal to the distance between c₁-d₁) or well beyond bases of setae d₁. This subgroup comprises of five species:

O. aceris (Shimer, 1869)

O. alpinus (McGregor, 1936)

O. endytus Pritchard & Baker, 1955

O. gambelii Tuttle & Baker, 1968

O. pustulosus Ehara, 1962

coffeae new species subgroup

Exemplar species. Acarus coffeae Nietner, 1861: 31.

Diagnosis (based on female). Seven tactile setae on tibia I, and dorsal hysterosomal setae c₁ long, reaching to (sub-equal to the distance between c₁-d₁) or well beyond bases of setae d₁. It comprises of 44 species:

O. bicolor (Banks, 1894)

O. brevipodus (Targioni-Tozzetti, 1878)

O. buschi (Reck, 1956)

O. chamaecyparisae Ma & Yuan, 1976

O. camelliae Ehara & Gotoh, 2007

O. castaneae Ehara & Gotoh, 2007

O. coffeae (Nietner, 1861)

O. coniferarum (McGregor, 1950)

O. cubensis (Livshits, 1968)

O. gotohi Ehara, 1999

O. gutierrezi Parsi, 1979

O. hamedaniensis Khanjani, Khanjani & Seeman, 2018

O. ilicis (McGregor, 1917)

O. judithae Meyer, 1974

O. juniperi Tuttle, Baker & Abbatiello, 1976

O. lagodechii Livshits & Mitrofanov, 1969

O. longiclavatus (Reck, 1953)

O. letchworthi Reeves, 1963

O. mangiferus (Rahman & Sapra, 1940)

O. metasequoiae Kuang, 1992

O. mitis Beglyarov & Mitrofanov, 1973

O. neocastaneae Arabuli & Gotoh, 2018

O. newcomeri (McGregor, 1950)

O. ochoai Meyer & Vargas, 1999

O. pruni Mitrofanov & Zapletina, 1973

O. penai Rimando, 1962

O. perditus Pritchard & Baker, 1955

O. peronis Pritchard & Baker, 1955

O. piceae (Reck, 1953)

O. platani (McGregor, 1950)

O. ponmanaiensis Karuppuchamy & Mohanasundaram, 1987

O. punicae (Hirst, 1926)

O. qilianensis Ma & Yuan, 1982

O. santoantoniensis Feres & Flechtmann, 1995

O. shojaeii Khanjani, Khanjani & Seeman, 2018

O. steinhaueri Flechtmann & Baker, 1970

O. tshimkenticus Wainstein, 1956

O. tsudomei Ehara, 1966

O. ununguis (Jacobi, 1905)

O. viranoplos Flechtmann, 1993

O. viridis (Banks, 1894)

O. vitis Zaher & Shehata, 1965

O. yothersi (McGregor, 1914)

O. yusti McGregor, 1959

Species groups and subgroups in the subgenus Reckiella

Oligonychus (Reckiella) is subdivided into two new species groups, the iseilemae species group and the exsiccator species group. The iseilemae species group is further categorized into two new species subgroups, the comptus species subgroup and the iseilemae species subgroup; whereas the exsiccator species group is categorized into four new species subgroups: the pritchardi species subgroup, the biharensis species subgroup, the gossypii species subgroup, and the exsiccator species subgroup.

The following two species of the subgenus Reckiella could not be assigned to any species group/subgroup, because they were briefly described and/or certain key characters of the female were not included:

O. annonicus (McGregor, 1955)

O. stenoperitrematus (Ugarov & Nikolskii, 1937)

iseilemae new species group

Exemplar species. Paratetranychus iseilemae Hirst, 1924: 524.

Diagnosis (based on female). Seven or less than seven (five or six) tactile setae on tibia I.

comptus new species subgroup

Exemplar species. Oligonychus comptus Meyer & Bolland, 1984: 218.

Diagnosis (based on female). Seven or less than seven (five or six) tactile setae on tibia I, and dorsal hysterosoma with a reticulate pattern of irregular and elongate elements medially. This subgroup includes only one species:

O. comptus Meyer & Bolland, 1984

iseilemae new species subgroup

Exemplar species. Paratetranychus iseilemae Hirst, 1924: 524.

Diagnosis (based on female). Seven or less than seven (five or six) tactile setae on tibia I, and dorsal hysterosoma ornamented with simple striations medially, reticulate pattern absent. This subgroup comprises of 12 species:

O. acugni (Livshits, 1968)

O. amnicolus Meyer, 1974

O. anonae Paschoal, 1970

O. bagdasariani Baker & Pritchard, 1962

O. beeri Estebanes & Baker, 1968

O. chiapensis Estebanes & Baker, 1968

O. fileno Mendonca, Navia & Flechtmann, 2010

O. iseilemae (Hirst, 1924)

O. megandrosoma Flechtmann & Alves, 1976

O. occidentalis Gutierrez, 1969

O. poutericola Feres & Flechtmann, 1986

O. themedae Meyer, 1974

exsiccator new species group

Exemplar species. Tetranychus exsiccator Zehntner, 1897: 572.

Diagnosis (based on female). More than seven (eight, nine or rarely ten) tactile setae on tibia I.

Due to unavailability of morphological information about the pattern of dorsal hysterosomal striae in female, the following one species could not be assigned to any of subgroup of the species group exsiccator:

O. bruneri (Livshits, 1968)

pritchardi new species subgroup

Exemplar species. Paratetranychus pritchardi McGregor, 1950: 350.

Diagnosis (based on female). More than seven (eight, nine or rarely ten) tactile setae on tibia I, five or six tactile setae on tibia II, and dorsal hysterosoma with uniform or wavy transverse striae between setae d₁-f₂ area, rarely with a mixture of wavy and oblique striae medially posterior to setae f₁. This subgroup comprises of 13 species:

O. calcis Baker & Pritchard, 1960

O. festucolus Beard & Walter, 2003

O. flechtmanni Tuttle, Baker & Sales, 1977

O. longipenis Feres & Flechtmann, 1995

O. mimosae Baker & Pritchard, 1962

O. psidii Flechtmann, 1967

O. psidium Estebanes & Baker, 1968

O. pritchardi (McGregor, 1950)

O. propetes Pritchard & Baker, 1955

O. quasipropetes Flechtmann, 1981

O. quercus Tuttle, Baker & Abbatiello, 1976

O. tiwakae Gutierrez, 1978

O. veranerae Baker & Pritchard, 1962

biharensis new species subgroup

Exemplar species. Paratetranychus biharensis Hirst, 1924: 69.

Diagnosis (based on female). More than seven (eight, nine or rarely ten) tactile setae on tibia I, seven tactile setae on tibia II, and dorsal hysterosoma with uniform or wavy transverse striae between setae d₁-f₂ area rarely with a mixture of wavy and oblique striae medially posterior to setae f₁. This subgroup includes ten species:

O. antherus Rimando, 1962

O. apohadrus Meyer, 1987

O. biharensis (Hirst, 1924)

O. hadrus Pritchard & Baker, 1955

O. hova Gutierrez, 1966

O. imberbei Meyer, 1974

O. macrostachyus Baker & Tuttle, 1972

O. malawiensis Meyer, 1974

O. pemphisi Gutierrez, 1970

O. sapienticolus Gupta, 1976

gossypii new species subgroup

Exemplar species. Paratetranychus gossypii Zacher, 1921: 183.

Diagnosis (based on female). More than seven (eight, nine or rarely ten) tactile setae on tibia I, and dorsal hysterosoma with various patterns of striae: longitudinal, irregular longitudinal, oblique, and with/without forming clear/inverted V/U-shaped striae between both setal pairs e₁-e₁ and f₁-f₁, or posterior to f₁-f₁, and/or striae forming a diamond pattern between e₁-f₂ area. This subgroup includes ten species, listed below:

O. gossypii (Zacher, 1921)

O. grewiae Meyer, 1965

O. intermedius Meyer, 1964

O. licinus Baker & Pritchard, 1960

O. litchii Lo & Ho, 1989

O. matthyssei Rimando, 1962

O. randriamasii Gutierrez, 1967

O. taiwanicus Tseng, 1990

O. trichardti Meyer, 1974

O. uruma Ehara, 1966

exsiccator new species subgroup

Exemplar species. Tetranychus exsiccator Zehntner, 1897: 572.

Diagnosis (based on female). More than seven (eight, nine or rarely ten) tactile setae on tibia I, and dorsal hysterosoma with various patterns of striae – longitudinal, irregular longitudinal, oblique and with/without forming clear/inverted V/U-shaped striae restricted to between setae e₁-e₁, or between and posterior to f₁-f₁; striae not forming a diamond pattern between these setae. This subgroup comprises of 69 species:

O. afrasiaticus (McGregor, 1939)

O. andrei Gutierrez, 1966

O. andropogonearum Gutierrez, 1969

O. anneke Baker & Pritchard, 1962

O. aquilinus Meyer, 1974

O. araneum Davis, 1968

O. barbatae Meyer, 1987

O. bessardi Gutierrez, 1966

O. calicicola Knihinicki & Flechtmann, 1999

O. campestris Meyer, 1987

O. castrensis Meyer, 1987

O. chazeaui Gutierrez, 1970

O. dactyloni Smiley & Baker, 1995

O. digitatus Davis, 1966

O. duncombei Meyer, 1974

O. ephamnus Beard & Walter, 2003

O. etiennei Gutierrez, 1982

O. exsiccator (Zehntner, 1897)

O. flexuosus Beer & Lang, 1958

O. formosanus Lo, 1969

O. gramineus (McGregor, 1950)

O. grastis Meyer, 1974

O. gratus Tseng, 1990

O. grypus Baker & Pritchard, 1960*

O. hortulanus Meyer, 1974

O. indicus (Hirst, 1923)

O. kadarsani Ehara, 1969

O. keiferi Tuttle & Baker, 1968

O. krantzi Zaher, Gomaa & El-Enany, 1982

O. leandrianae Gutierrez, 1970

O. manishi Gupta, 1979

O. martensis Meyer, 1974

O. mcgregori (Baker & Pritchard, 1953)

O. menezesi Flechtmann, 1981

O. modestus (Banks, 1900)

O. mexicanus (McGregor & Ortega, 1953)

O. nasutus Meyer, 1974

O. nelensis Meyer, 1974

O. neoplegas Meyer, 1964

O. neopratensis Meyer, 1974

O. neotylus Zeity & Srinivasa, 2016

O. obliquus Ehara & Masaki, 2001

O. ocellatus Meyer, 1987

O. oenotherae Smiley & Baker, 1995

O. orthius Rimando, 1962

O. oryzae (Hirst, 1926)

O. palus Beard, 2008

O. pennisetum Meyer, 1974

O. plegas Baker & Pritchard, 1960

O. plicarum De Leon, 1957

O. pratensis (Banks, 1912)*

O. rubicundus Ehara, 1971

O. rusticus Meyer, 1974

O. shinkajii Ehara, 1963

O. sacchari (McGregor, 1942)

O. saccharinus Baker & Pritchard, 1960

O. saccharoides Baker & Tuttle, 1972

O. sayedi Zaher, Gomaa & El-Enany, 1982

O. senegalensis Gutierrez & Etienne, 1981

O. simus Baker & Pritchard, 1960

O. stickneyi (McGregor, 1920)

O. triandrae Meyer, 1974

O. turbelli Beard & Walter, 2003

O. tylus Baker & Pritchard, 1960

O. velascoi Rimando, 1962

O. virens Gutierrez, 1969

O. waltersi Meyer, 1987

O. zanclopes Beard & Walter, 2003

O. zeae (McGregor, 1955)

Ungrouped Oligonychus species

Among 211 Oligonychus species, the 17 species listed below were described based on females alone, with the males being unknown in the original and subsequent descriptions (14 of which are also listed as species inquirendae (see further below). Due to the unavailability of critical morphological information regarding the aedeagus shape/orientation, these species could not be assigned to any of the subgenera, species groups or subgroups:

O. amiensis Ehara & Gotoh, 2007**

O. caucasicus (Reck, 1956)

O. changi Tseng, 1980

O. conostegiae Tuttle, Baker & Abbatiello, 1974

O. daleae Tuttle, Baker & Abbatiello, 1976

O. jiangxiensis Ma & Yuan, 1980

O. longus Chaudhri, Akbar & Rasool, 1974

O. mactus Tseng, 1990

O. nielseni Reeves, 1963

O. picei (Canestrini, 1889)

O. primulae (Oudemans, 1931)

O. proteae Meyer & Ryke, 1959

O. pongami Sivakumar & Kunchithapatham, 2014

O. subtropicus Tseng, 1980

The term species complex, also referred to as sibling or cryptic species complex, is an informal taxonomic term or “open nomenclature qualifier” that is used when two/more morphologically indistinguishable but biologically separate species are present or several distinct species are suspected to exist under one name, which results in the taxonomic uncertainty of a taxon (Sigovini et al. 2016). Species complexes are notoriously difficult to resolve when based on morphology alone (Pritchard and Baker 1955). However, such complex taxonomic issues have been efficiently and effectively addressed in different tetranychid genera, e.g., Mononychellus Wainstein, Oligonychus, and Tetranychus through the combination of morphological, molecular, and biological data (Navajas et al. 1994, 2001; Gotoh et al. 1998, 2007, 2009; Matsuda et al. 2013; Zeity et al. 2017). Therefore, integrative taxonomic approaches are needed to clarify the actual status of all closely related species, and species complexes, in the genus Oligonychus.

Within the genus Oligonychus, we recognized five new species complexes, viz. the afrasiaticus species complex, the litchi species complex, the punicae species complex, the plegas species complex and the tylus species complex, along with two previously highlighted complexes, the sacchari complex (Khanjani et al. 2018) and the pratensis complex (Pritchard and Baker 1955; Meyer 1974; Li et al. 2018). The punicae complex is placed in the subgenus Oligonychus, while the other six species complexes are placed in the subgenus Reckiella. The punicae species complex includes four morphologically similar Oligonychus species, O. punicae, O. mangiferus, O. yusti, and O. vitis. The males and females of each of these four species share similar morphology, including a downturned aedeagus, and based on the currently available diagnostics, species of the punicae complex are very difficult to distinguish from each other. The afrasiaticus complex includes O. aquilinus, O. afrasiaticus, O. keiferi, and O. menezesi. The litchii complex includes only O. litchii and O. taiwanicus. The plegas complex includes O. araneum, O. orthius, O. plegas, O. sayedi, and O. velascoi. The tylus complex includes O. etiennei, O. senegalensis and O. tylus. Those Oligonychus species which belonging to the afrasiaticus, litchii, plegas, and tylus complexes can be hardly distinguished using aedeagus shape, number of tactile/sensory setae on tibia I and tactile setae behind to proximal duplex on tarsus I in male, length-width ratio of male/female palp spinneret and comparative length of proximo-ventral spur/main claw of male empodium I. Species that belong to the sacchari complex (O. sacchari and O. saccharinus) and the pratensis complex (O. pratensis, O. shinkajii, and O. virens) are difficult discriminate from each other using the available morphological characters because they are variable in their expression.

Presence and absence of para-anal setae in the genus Oligonychus

Lindquist (1985) used the form and position of the H setae when determining setal homologies and recognized that both of the para-anal setae h₂ and h₃ are always present, and that the clunal seta h₁ is always absent in the genera Oligonychus and Tetranychus. This nomenclature was first interpreted by Oudemans (1930) and then later by Pritchard and Baker (1952), and as is followed here.

The setal shapes can be helpful when determining the presence or absence (and hence names) of para-anal setae in Oligonychus and its closely related genera, as previously highlighted by Lindquist (1985) and Seeman and Beard (2011). Moreover, the form of setae h₁ in different genera, for example Mixonychus and Schizotetranychus, are similar to other dorsal setae (Figs 1A, B), whereas setae h₂ and h₃ are usually similar in form to the anals, genitals, and other ventral setae, in all Tetranychini genera (Figs 2, 3).

Figure 1.

Shape of seta h₁ is similar to other dorsal body setae in various genera of the tribe Tetranychini in e.g. A Mixonychus and B Schizotetranychus. Scale bar: 30 μm.

Figure 2.

Shape of setae A h₂ and B h₃ are similar to other ventral body setae in all the genera of the tribe Tetranychini in e.g. Oligonychus. Scale bar: 30 μm.

Figure 3.

Shape of setae h₂ and h₃ are similar to other ventral body setae in all the genera of the tribe Tetranychini in e.g Tetranychus. Scale bar: 30 μm.

The term “para-anal setae” was introduced by Pritchard and Baker (1955) and can be confusing when interpreting setae in the Tetranychini. So, for practical purposes, the first couplet (page 9, section 2.3) of the diagnostic key to genera of the tribe Tetranychini provided in the world catalogue of spider mites by Bolland et al. (1998) may be interpreted by users as, “3 pairs of h setae present, h_1-3” versus “2 pairs of h setae present, h_2-3 and h₁ absent”.

Key to subgenera, species groups, and subgroups of the genus Oligonychus Berlese

1	In lateral view, male aedeagus with shaft bending ventrad	(subgenus Oligonychus Berlese) 2
–	In lateral view, male aedeagus with shaft bending dorsad, or shaft initially bending dorsad then sigmoid or curved downward distally	(subgenus Reckiella Tuttle and Baker) 6
2	Female with 8 or 9 tactile setae on tibia I	*(peruvianus* species group) 3**
–	Female with 5, 6 or 7 tactile setae on tibia I	*(coffeae* new species group) 4**
3	Female with dorsal opisthosomal setae c₁ long, reaching well beyond bases of setae d₁	smithi new species subgroup
–	Female with dorsal opisthosomal setae c₁ short, not reaching bases of setae d₁, almost one-half to three-quarters as long as the distance between c₁-d₁	peruvianus new species subgroup
4	Female with dorsal opisthosomal setae c₁ short, not reaching bases of d₁, almost one-half to three-quarters as long as the interval to d₁	subnudus species subgroup
–	Female with dorsal opisthosomal setae c₁ long, reaching to (sub-equal to the distance between c₁-d₁) or well beyond bases of setae d₁	5
5	Female with 5 or 6 tactile setae on tibia I	aceris species subgroup
–	Female with 7 tactile setae on tibia I	coffeae new species subgroup
6	Female with 5, 6 or 7 tactile setae on tibia I	*(iseilemae* new species group) 7**
–	Female with 8, 9 or 10 tactile setae on tibia I	*(exsiccator* new species group) 8**
7	Medial dorsal hysterosomal striae forming a reticulated pattern of irregular, elongate elements in female	comptus new species subgroup
–	Medial dorsal hysterosomal striae without a reticulated pattern in female	iseilemae new species subgroup
8	Female with dorsal hysterosomal striae medially between setae d₁-f₂ typically transverse or wavy transverse, rarely with a mixture of wavy longitudinal and oblique striae posterior to setae f₁	9
–	Female with dorsal hysterosomal striae typically longitudinal, irregular longitudinal, oblique, or forming a V/U-shaped pattern, anywhere medially between d₁-f₂ area	10
9	Female with 5 or 6 tactile setae on tibia II	pritchardi new species subgroup
–	Female with 7 tactile setae on tibia II	biharensis new species subgroup
10	Female with medial dorsal hysterosomal striae longitudinal, irregular longitudinal, oblique with/without forming a V/U-shaped pattern between setae e₁ and e₁ and between/posterior to f₁ and f₁, and with/without forming a diamond pattern between setal rows E and F (Fig. 4A)	gossypii new species subgroup
–	Female with medial dorsal hysterosomal striae longitudinal (Fig. 4B), irregular longitudinal (Fig. 4C), oblique with/without forming a V/U-shaped pattern (Fig. 4D) between either setae e₁ and e₁ or between/posterior to f₁ and f₁, and not forming a diamond pattern between setal rows E and F	exsiccator new species subgroup

Figure 4.

Shape of different striae patterns A longitudinal between setae e₁-e₁ and between f₁-f₁, in O. randriamasii Gutierrez (redrawn from original description, Gutierrez 1967) B longitudinal between/posterior to setae f₁-f₁, in O. orthius Rimando (redrawn from re-description, Beard et al. 2003) C irregular longitudinal between/posterior to setae f₁-f₁ D oblique with slightly forming V-shaped pattern between setae f₁-f₁, in O. turbbelli Beard and Walter (redrawn from original description, Beard et al. 2003). Scale bars: 50 μm (B, C, D); 100 μm (A).

Acknowledgements

The authors would like to extend their sincere appreciation to the Deanship of Scientific Research at the King Saud University for funding this research through Research Group no. RG 1438-055. We are also thankful to Dr. Amgad A. Saleh and Dr. Jawwad Hassan Mirza (Department of Plant Protection, King Saud University) for editing and reviewing the manuscript with their constructive and useful comments that have greatly improved it. Special thanks to the respected reviewers Dr. Jennifer J. Beard (Queensland Museum, South Brisbane, Australia) and Dr. Tetsuo Gotoh (Ryutsu Keizai Univesity, Japan) for their constructive comments and scientific editing on the manuscript that have significantly improved it.

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Zeity M, Srinivas N, Gowda CC (2017) Are Tetranychus macfarlanei Baker & Pritchard and Tetranychus malaysiensis Ehara (Acari: Tetranychidae) one species? Morphological and molecular evidences for synonymy between these two spider mite species and a note on invasiveness of T. macfarlanei. Systematic and Applied Acarology 22: 467–476. https://doi.org/10.11158/saa.22.4.3

1 We observed a conflict between descriptions and illustrations of O. verduzcoi regarding comparative length of setae c ₁ . It is described as shorter in original description by Estebanes and Baker (1968) or reaching to the bases of setae d ₁ by Tuttle et al. (1976). We followed the original description (Estebanes and Baker 1968) and assigned this species to the subnudus species subgroup.

2 Meyer (1974) synonymized O. monsarratiGutierrez (1967) with O. grypus. However, other authors considered it to be a valid species (Bolland et al. 1998; Migeon 2015), and still included in species list on spider mites web (Migeon and Dorkeld 2021). In the present study, we agree with Meyer (1974) by considering it a junior synonym of O. grypus.

3 Oigonychus pratensis is placed in the exsiccator subgroup based on the reports by various authors (McGregor 1950; Pritchard and Baker 1955; Baker and Pritchard 1962; Estebanes and Baker 1968; Tuttle and Baker 1968; Chaudhri et al. 1974; Tuttle et al. 1976; Baker and Tuttle 1994; Jeppson et al. 1975; Meyer 1987) that the female of this species has longitudinal, irregular longitudinal or oblique striae between setae f ₁ -f ₁ . Recently, however, Li et al. (2018) reported on a population of O. pratensis with longitudinal striae consistently between both setal pairs e ₁ -e ₁ and f ₁ -f ₁ , which is a diagnostic character of the gossypii species subgroup. Because this morphological variation of O. pratensis is consistent and only expressed in China, we believe that this population could actually represent a species in the gossypii subgroup, and that it is not O. pratensis at all. We suggest the use of an integrative taxonomical approach based on both morphological and molecular data to determine its true identity.

4 The available molecular data for O. amiensis (Matsuda et al. 2012) is proved association with the subgenus Oligonychus. Furthermore, based on female morphology, it belongs to the species group/subgroup coffeae.

﻿Abstract

Keywords

﻿Introduction

﻿Materials and methods

﻿Results and discussion

Family Tetranychidae Donnadieu

Tribe Tetranychini Reck

﻿Genus Oligonychus Berlese, 1886.

Type species

Diagnosis

﻿Taxonomic review of the genus Oligonychus

Subdivision of the genus Oligonychus

Species complexes in the genus Oligonychus

Para-anal setae in the genus Oligonychus

﻿Subgeneric division of the genus Oligonychus

Subgenus Oligonychus Berlese

Subgenus Reckiella Tuttle & Baker

﻿Subdivision of Oligonychus species into groups and subgroups

﻿Species groups and subgroups in the subgenus Oligonychus

peruvianus species group (sensu Pritchard & Baker, 1955)

smithi new species subgroup

peruvianus new species subgroup

coffeae new species group

subnudus species subgroup (sensu Pritchard and Baker 1955)

aceris species subgroup (sensu Pritchard and Baker 1955)

coffeae new species subgroup

﻿Species groups and subgroups in the subgenus Reckiella

iseilemae new species group

comptus new species subgroup

iseilemae new species subgroup

exsiccator new species group

pritchardi new species subgroup

biharensis new species subgroup

gossypii new species subgroup

exsiccator new species subgroup

Ungrouped Oligonychus species

﻿Species inquirendae in the genus Oligonychus

﻿1. Oligonychus picei (Canestrini, 1889)

Host and distribution

Remarks

﻿2. Oligonychus primulae (Oudemans, 1931)

Host and distribution

Remarks

﻿3. Oligonychus kobachidzei (Reck, 1947)

Host and distribution

Remarks

﻿4. Oligonychus caucasicus (Reck, 1956)

Host and distribution

Remarks

﻿5. Oligonychus proteae Meyer & Ryke, 1959

Host and distribution

Remarks

﻿6. Oligonychus nielseni Reeves, 1963

Host and distribution

Remarks

﻿7. Oligonychus longus Chaudhri, Akbar & Rasool, 1974

Host and distribution

Remarks

﻿8. Oligonychus conostegiae Tuttle, Baker & Abbatiello, 1974

Host and distribution

Remarks

﻿9. Oligonychus daleae Tuttle, Baker & Abbatiello, 1976

Host and distribution

Remarks

﻿10. Oligonychus changi Tseng 1980

Host and distribution

Remarks

﻿11. Oligonychus jiangxiensis Ma & Yuan, 1980

Host and distribution

Remarks

﻿12. Oligonychus subtropicus Tseng, 1980

Host and distribution

Remarks

﻿13. Oligonychus mactus Tseng, 1990

Host and distribution

Remarks

﻿14. Oligonychus pongami Sivakumar & Kunchithapatham, 2014

Host and distribution

Remarks

﻿Species complexes in the genus Oligonychus

Abstract

Introduction

Materials and methods

Results and discussion

Genus Oligonychus Berlese, 1886.

Taxonomic review of the genus Oligonychus

Subgeneric division of the genus Oligonychus

Subdivision of Oligonychus species into groups and subgroups

Species groups and subgroups in the subgenus Oligonychus

Species groups and subgroups in the subgenus Reckiella

Species inquirendae in the genus Oligonychus

1. Oligonychus picei (Canestrini, 1889)

2. Oligonychus primulae (Oudemans, 1931)

3. Oligonychus kobachidzei (Reck, 1947)

4. Oligonychus caucasicus (Reck, 1956)

5. Oligonychus proteae Meyer & Ryke, 1959

6. Oligonychus nielseni Reeves, 1963

7. Oligonychus longus Chaudhri, Akbar & Rasool, 1974

8. Oligonychus conostegiae Tuttle, Baker & Abbatiello, 1974

9. Oligonychus daleae Tuttle, Baker & Abbatiello, 1976

10. Oligonychus changi Tseng 1980

11. Oligonychus jiangxiensis Ma & Yuan, 1980

12. Oligonychus subtropicus Tseng, 1980

13. Oligonychus mactus Tseng, 1990

14. Oligonychus pongami Sivakumar & Kunchithapatham, 2014

Species complexes in the genus Oligonychus

Presence and absence of para-anal setae in the genus Oligonychus

Key to subgenera, species groups, and subgroups of the genus Oligonychus Berlese

Acknowledgements

References