# Alpha, Beta and Gamma Taxonomy of Biocontrol Agent Diaeretiella rapae (Hymenoptera, Braconidae)

## TL;DR

This study reclassifies the parasitoid wasp Diaeretiella rapae as a member of the genus Aphidius based on genetic and morphological evidence.

## Contribution

The paper provides new taxonomic insights by synonymizing Diaeretiella rapae with Aphidius and resolving its long-standing classification.

## Key findings

- Molecular analysis of the COI gene revealed 23 haplotypes with a mean genetic distance of 0.8%.
- Phylogenetic analysis placed D. rapae within the Aphidius clade with genetic distances consistent with intraspecific variation.
- Morphological traits of D. rapae align with those of the genus Aphidius, confirming its reclassification.

## Abstract

Diaeretiella rapae is a widespread aphid parasitoid that targets various aphids, especially those found on cruciferous plants and cereals. Since 1855, the species changed its taxonomic position many times. In this study, specimens of Diaeretiella were analyzed using both molecular and morphological methods. The analysis of mitochondrial COI region revealed 23 different haplotypes within the genus. Phylogenetic analysis placed D. rapae within the Aphidius clade, with genetic distances that are within the range of intraspecific genetic distances of Aphidius. Morphological comparisons showed that D. rapae shares key morphological characters with species in the genus Aphidius. Based on the results, we synonymize D. rapae as A. rapae and designate genus Diaeretiella as junior synonym of Aphidius.

Diaeretiella rapae (McIntosh, 1855) is a cosmopolitan koinobiont endoparasitoid of aphids, occurring mainly on crucifers and cereals. From description, it has changed several genera and has about 20 synonyms. The specimens for this study were collected between 1989 and 2023 from sites across Europe and the Middle East. For molecular analysis, the barcode mitochondrial gene COI was used, and morphological analysis was conducted with other Aphidius species. Morphologically, D. rapae falls within the determined variability of the same characters of the genus Aphidius. Dieretiella rapae comprised 23 haplotypes with a mean genetic distance between haplotypes of 0.8%. Phylogenetically, D. rapae is nested within Aphidius species with a genetic distance of 2.1% to 11.3%, which is within the range of other Aphidius species. Our results on morphological and molecular level confirm that D. rapae belongs to the genus Aphidius.