A comprehensive taxonomic assessment of the most agriculturally important and highly diverse spider mite genus,OligonychusBerlese (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, namelyOligonychusBerlese (aedeagus downturned) andReckiellaTuttle & Baker (aedeagus upturned), are valid in the genusOligonychus. The subgeneraHomonychusWainstein,MetatetranychoidesWainstein, andWainsteiniellaTuttle & 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, andperuvianus) and 11 species subgroups (aceris,biharensis,coffeae,comptus,exsiccator,gossypii,iseilemae,peruvianus,pritchardi,smithi, andsubnudus) are suggested in the subgeneraOligonychusandReckiella. FourteenOligonychusspecies are proposed as species inquirendae, and potential cryptic species complexes in the genusOligonychusare briefly highlighted. It is agreed that the clunal setah₁is always absent, while the para-anal setaeh₂andh₃are always present in the genusOligonychus.A key to subgenera, species groups, and species subgroups of the genusOligonychusis provided.

To elucidate the taxonomic problems in species delineation within the Oligonychus punicae complex (O. punicae, O. mangiferus, and O. vitis) (Acari: Prostigmata: Tetranychidae), we performed morphological and molecular investigations on mite samples, collected from different hosts/countries. Thirty-nine samples of punicae complex, collected from Egypt, Pakistan, and Saudi Arabia (SA), did not show any considerable morphological differences in females and males. All 39 samples of the punicae complex resembled the original description of O. punicae, while the claimed Mexican O. punicae was distinctively different based on male aedeagus. Molecularly, the low nucleotide diversity ranged from 0% to 2.1% (ITS2-rDNA) and 0% to 1% (COI-mtDNA), and was observed among various DNA sequences of the punicae complex from Egypt, India, Israel, Pakistan, and SA, confirming their identity as one species. The high genetic divergence ranged from 17.2% to 18.8% (ITS2) and 9.2% to 10.2% (COI), observed between the claimed Mexican O. punicae and all other sequences of the punicae complex, indicating that the Mexican sample do not belong to O. punicae. Basing our findings on both morphological and molecular data, we can conclude that O. mangiferus and O. vitis are synonymized with O. punicae. Additionally, this study reveals that the claimed Mexican O. punicae needs to be re-identified.

DNA barcoding technology using short DNA sequences has emerged as an efficient and reliable tool for identifying, confirming, and resolving closely related taxa. This study used ITS2-rDNA and mtCOI DNA sequences to confirm the identity of eight Oligonychus species, representing 68 spider mite samples, collected mainly from Saudi Arabia (SA) and some from Mexico, Pakistan, USA, and Yemen. The intraspecific nucleotide divergences of the studied Oligonychus species ranged from 0% to 1.2% for ITS2 and 0% to 2.9% for COI. However, the interspecific nucleotide divergences were distinctly higher than the intraspecific ones and ranged from 3.7% to 51.1% for ITS2 and 3.2% to 18.1% for COI. Furthermore, molecular data correctly confirmed the species identity of 42 Oligonychus samples lacking males, including a previously claimed sample of O. pratensis from SA. High genetic variations were detected in two Oligonychus species: O. afrasiaticus (McGregor) (nine ITS2 and three COI haplotypes) and O. tylus Baker and Pritchard (four ITS2 and two COI haplotypes). In addition, ITS2- and COI-based phylogenetic trees confirmed the subdivision of the genus Oligonychus. In conclusion, integrative taxonomic approaches are vital to resolve the closely related Oligonychus species, identify the samples lacking male specimens, and assess phylogenetic relationships within and among species.

Spider mite fauna of the genus Oligonychus Berlese (Acari: Prostigmata: Tetranychidae) was comprehensively explored from natural and cultivated vegetation in Saudi Arabia (SA), during the years 2018 to 2020. One new species, Oligonychus washingtoniae sp. nov., and three new records, O. coniferarum (McGregor, 1950), O. dactyloni Smiley & Baker, 1995, and O. tylus Baker & Pritchard, 1960, are reported for the first time from SA. The new species, O. washingtoniae sp. nov. is described and illustrated from Washingtonia filifera (Lindl.) H.Wendl. (Arecaceae). The species O. dactyloni, and O. tylus are re-described, which were briefly described previously.

The predatory mite Cydnoseius negevi (Swirski and Amitai) is mostly found in association with the old world date mite (OWDM), Oligonychus afrasiaticus (McGregor) and occasionally with the two spotted spider mite (TSSM), Tetranychus urticae Koch. We evaluated the predation efficiency and preference of lab-reared (LR) and field-collected (FC) populations of C. negevi on larvae and nymphs (juveniles) of OWDM and TSSM. No significant effect of long-term pollen feeding on predation efficiency or prey-stage preference was observed when comparing LR and FC populations of C. negevi. However, significant differences were observed between LR and FC populations of C. negevi for prey species preference, the LR population of C. negevi significantly preferred OWDM over TSSM. Maximum predation efficiency was observed in prey species preference tests (average 29–31 juveniles of OWDM and TSSM together) as compared to predation efficiency/prey stage preference tests (average 20–24 and 16-22 juveniles of OWDM and TSSM, respectively) within 24 h. The results revealed that C. negevi somewhat preferred OWDM than TSSM. The availability of pollen did not affect the predation efficiency of C. negevi against both pest species.