Abstract
The mite Thyreophagus entomophagus is a cosmopolitan species of significant economic importance in biocontrol applications, serving as a factitious prey for the mass rearing of predatory mites. This species has been reported from a variety of habitats. However, the taxonomic reliability of its name is questionable due to inconsistencies in historical species identifications, the absence of type specimens, and misidentified GenBank sequences. Here, to address these issues and to standardize the nomenclature, we redescribe Thyreophagus entomophagus based on a commercial culture with known COX1 barcoding sequence data and designate a neotype from this culture. As part of delimiting the species boundaries of Th. entomophagus, the question of whether this species forms heteromorphic deutonymphs is particularly important. While the literature suggests that most populations lack them, at least one population in Germany has been reported to produce heteromorphic deutonymphs. However, after careful examination, we identified this population as a new species, Thyreophagus holda, indicating that previous identifications of this population as Th. entomophagus were incorrect. The absence of the heteromorphic deutonymphal stage is a beneficial trait for mass production, as it simplifies the life cycle by eliminating the energetically costly heteromorphic deutonymph. Our preliminary molecular phylogenetic analyses of Th. entomophagus and other species of Thyreophagus indicate that the loss of heteromorphic deutonymphs and the emergence of asexual reproduction (another beneficial trait for mass production) are derived traits that arose after the divergence of the most recent common ancestor of Thyreophagus. These insights enhance our understanding of the evolutionary traits that increase the effectiveness of Th. entomophagus and related species in biocontrol settings. Our study points to the need for additional bioprospecting efforts to identify new candidate species for biocontrol that possess both asexual reproduction and the absence of heteromorphic deutonymphs.