Multiple Data Demonstrate That Bacteria Regulating Reproduction Could Be Not the Cause for the Thelytoky of Diglyphus wani (Hymenoptera: Eulophidae)

Abstract

In Hymenoptera parasitoids, the reproductive mode is arrhenotoky, while a few species reproduce by thelytoky. The thelytoky of Hymenoptera parasitoids is generally genetically determined by the parasitoids themselves or induced by bacteria, including Wolbachia, Cardinium, and Rickettsia. Diglyphus wani (Hymenoptera: Eulophidae), a recently reported thelytokous species is a main parasitoid attacking agromyzid leafminers. To assess whether endosymbionts induce thelytoky in D. wani, we performed universal PCR detection and sequenced the V3-V4 region of 16S ribosomal RNA gene. In addition, bacteria were removed through high-temperature and antibiotic treatments, and the localized bacteria were detected using FISH. Based on general PCR detection, Wolbachia, Cardinium, Rickettsia, Arsenophonus, Spiroplasma, and Microsporidia were absent in laboratory and field individuals of thelytokous D. wani. Furthermore, 16S rRNA gene sequencing revealed that the dominant endosymbionts in thelytokous D. wani were not reproductive manipulators. High-temperature and antibiotic treatment for five consecutive generations cannot reverse the thelytokous pattern of D. wani, and no male offspring were produced. Moreover, no bacterial spots were found in the ovaries of D. wani. Thus, it is considered that the thelytoky of D. wani does not result in the presence of endosymbionts. This species is thus the second reported eulophid parasitoid whose thelytoky appears not to be associated with endosymbionts.

The thelytokous strain of the parasitoid Neochrysocharis formosa outperforms the arrhenotokous strain in reproductive capacity and biological control of agromyzid leafminers

“…Equations (7)(8)(9)(10)(11)(12) were also applied to calculate parameters of parasitism (where c xj was the parasitism rate) and host stinging (where c xj was the host-stinging rate). The number of host-killing events was the sum of host-feeding, parasitism, and hoststinging events.…”

“…8 Although arrhenotoky is the most common reproductive mode in Hymenoptera, thelytoky also exists in the Hymenoptera, especially in the Eulophidae, Cynipoidea, and Chalcidoidea superfamilies. [10][11][12] Several thelytokous parasitoids are commonly used as biocontrol agents against important pests, such as the greenhouse whitefly parasitoid Encarsia formosa 13,14 and lepidopteran pests parasitoids Trichogramma spp. 15,16 In terms of biological control, thelytokous strains offer certain advantages over arrhenotokous strains as biocontrol agents under ideal conditions: (i) they can reduce production costs because they use all eggs and host resources to produce female-only offspring for mass rearing before augmentative biological control; and (ii) they can quickly establish stable populations in low-density host/parasitoid environments without needing to mate with male parasitoids in augmentative biological control.…”

“…In contrast, thelytokous females produce unfertilized eggs, resulting in only females 8 . Although arrhenotoky is the most common reproductive mode in Hymenoptera, thelytoky also exists in the Hymenoptera, especially in the Eulophidae, Cynipoidea, and Chalcidoidea superfamilies 10–12 . Several thelytokous parasitoids are commonly used as biocontrol agents against important pests, such as the greenhouse whitefly parasitoid Encarsia formosa 13,14 and lepidopteran pests parasitoids Trichogramma spp 15,16 .…”

Apomixis for no bacteria-induced thelytoky in Diglyphus wani (Hymenoptera: Eulophidae)

“…Here, we focused on the dominant natural enemy of agromyzid leafminers, Diglyphus wani, which has been identified as thelytokous and arrhenotokous (Du et al, 2021). Diglyphus wani was not infected with Wolbachia, Rickettsia, Cardinium, or any other known bacterial reproductive manipulator (Du et al, 2022). This study aimed to explore the cytological process of restoring ploidy in thelytokous D. wani using cytological observation and microsatellite genetic markers.…”

“…The most common form of reproduction in Hymenoptera with haplodiploid sex determination is arrhenotokous, in which haploid males develop from unfertilized eggs and diploid females develop from fertilized eggs ( Luck et al, 1993 ; Heimpel and de Boer, 2008 ). However, more than 500 Hymenoptera species have been documented as thelytokous (unfertilized eggs which generally develop into diploid females) ( van der Kooi et al, 2017 ; Du et al, 2022 ).…”