# Typification of the Economically Important Species Thyreophagus entomophagus (Acari: Astigmata: Acaridae) Used for the Industrial Production of Predatory Mites: The Designation of a Neotype with Detailed Morphological and DNA Sequence Data

## TL;DR

This paper clarifies the identity of a mite species used in agriculture, designating a new standard specimen and revealing a new species, which helps improve biological pest control methods.

## Contribution

The designation of a neotype for Thyreophagus entomophagus and the discovery of a new species, Thyreophagus holda, resolve taxonomic confusion and highlight traits beneficial for mass production in biocontrol.

## Key findings

- Thyreophagus entomophagus lacks a specialized deutonymph stage, simplifying mass production.
- A previously misidentified population is a new species, Thyreophagus holda.
- Asexual reproduction and absence of deutonymphs are derived traits beneficial for biocontrol.

## Abstract

The mite Thyreophagus entomophagus is widely used in agriculture as a food source for breeding predatory mites, which are important for biological pest control. However, the identity of this species has been uncertain due to its incorrect identifications involving both morphology and DNA sequence data. To resolve this, we carefully examined a commercial population, selecting a new type specimen from this population to standardize its name. We also discovered that a population previously thought to belong to this species is actually a new species, Thyreophagus holda. These findings clarify that Th. entomophagus lacks a specialized life stage (deutonymph) in its life cycle, making it easier and more efficient to mass-produce. Our phylogenetic analysis shows that this trait, along with asexual reproduction, evolved after the origin of the genus Thyreophagus. We suggest that these traits—being asexual and lacking the deutonymph stage—are ideal for effective mass production in biological pest control. Our study emphasizes the need to explore more mites with these beneficial traits, which could enhance sustainable agricultural practices and reduce the need for chemical pesticides.

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.