rna-interference-egg-parasitoid-trichogramma-dendrolimi

RNA Interference in the Egg Parasitoid, <em>Trichogramma dendrolimi</em> Matsumura

The egg parasitoids, Trichogramma spp, are recognized as efficient biological control agents against various lepidopteran pests in agriculture and ...

Shenyang Agricultural University

Chinese Academy of Agricultural Sciences

Intersex is an intermediate stage of sexual differentiation in insects. Determining intersex morphology and the cause of its production will aid in the understanding of the mechanism of sexual differentiation in insects. In this paper, -infected  ( ) that shows thelytokous parthenogenesis were used as subjects. In order to determine the causes of the  intersex and the influence of parental generation temperature on gradual changes in secondary masculinization in intersex offspring, we examined the occurrence of intersex offspring (F and F generation) after the parental generations were treated with high temperature (27, 29, 31, and 33 °C) and described the external morphology of the intersexes. The results showed that the  parental generation temperature is positively correlated with the probability of intersex offspring. The probability of F intersex is significantly higher than that of F intersex in different high temperature. The degree of secondary masculinization in  intersexes increases as parental generation temperature increases. In addition, our study first identified 11 intersex types in  and found that the primary and secondary sexual characteristics showed a regular distribution. We also found that the D type and H type of intersex have the highest frequency of appearance. The external genitalia of most intersexes were female, and only three intersex types have male external genitalia. Conclusions were ultimately obtained:  is a direct factor that causes the occurrence of intersexes, while high temperature is an indirect factor that determines the external morphology of intersexes. The effects of high temperature on  intersexes is passed through the parental generation to offspring, and this maternal effect weakens as the number of generations increases. In  intersex individuals, most exhibit female primary sexual characteristics, and secondary sexual characteristics exhibit signs of masculinization.

Gradual, temperature-induced change of secondary sexual characteristics in  infected with parthenogenesis-inducing .

Trichogramma dendrolimi is one of the most successful biocontrol agents in China. However, an inundative condition is necessary to obtain acceptable parasitism effect. A good solution to this is the application of its thelytokous counterparts which unfortunately are scarce in field. We here report the first case of a natural T. dendrolimi population in China comprising both bisexual wasps and an extremely low proportion of thelytokous wasps. These two forms of T. dendrolimi are phylogenetically related based on the reconstructions of ITS-2 and COI genes. Also, the phylogenetic results suggested a potentially Wolbachia-drived ITS-2 variation. The expression of thelytoky was hardly affected by temperature, which might help control Asian corn borer and Dendrolimus punctatus. Wolbachia are responsible for current thelytoky according to phylogenetic analyses, antibiotic treatment and introgression experiment. We also present the third case of paternal sex ratio chromosome that restrains the expansion of Wolbachia. Moreover, the low frequency of thelytoky may be common in natural populations. Consequently if for biological control it is determined that a thelytokous strain is to be preferred, then large number of field collected females should be set up as isofemale lines, to detect the rare thelytoky.

Co-occurrence of thelytokous and bisexual Trichogramma dendrolimi Matsumura (Hymenoptera: Trichogrammatidae) in a natural population.

Thelytokous Wolbachia-infected Trichogramma spp. are widely used egg parasitoids against lepidopteran pests in biological control programs. Wolbachia may manipulate host wasps for superparasitism and is sensitive to temperature. To explore effects of temperature and superparasitism, we compared fitness parameters and Wolbachia-mediated phenotype of thelytokous Wolbachia-infected Trichogramma dendrolimi between those emerging from superparasitised or single-parasitised hosts at 17, 21, 25, or 29 °C. Infected mothers of T. dendrolimi showed reduced superparasitism and parasitism increased with temperature. Wolbachia titre decreased with temperature when females emerged from singly-parasitised hosts, but there was no correlation in superparasitised hosts. Females showed higher Wolbachia titres at 21, 25, or 29 °C when developing from superparasitised hosts. The daily male ratio of offspring increased with temperature, and the day-age threshold for 5%, 50%, or 95% daily male ratio decreased with temperature in both parasitism forms. Females that emerged from superparasitised hosts had a shorter life span and reduced fecundity. These results indicate that Wolbachia may affect host behaviour by increasing superparasitism to enhance its spread, but this has negative effects on thelytokous Wolbachia-infected T. dendrolimi.

Effects of temperature and superparasitism on quality and characteristics of thelytokous Wolbachia-infected Trichogramma dendrolimi Matsumura (Hymenoptera: Trichogrammatidae) during mass rearing.

Attributes of pest species like host range are frequently reported as being evolutionarily constrained and showing phylogenetic signal. Because these attributes in turn could influence the abundance and impact of species, phylogenetic information could be useful in predicting the likely status of pests. In this study, we used regional (China) and global datasets to investigate phylogenetic patterns in occurrence patterns and host ranges of spider mites, which constitute a pest group of many cropping systems worldwide.

Phylogenetic signals in pest abundance and distribution range of spider mites.

Trichogramma dendrolimi has been widely used in augmentative biocontrol of lepidopteran pests in China. In mass production of T. dendrolimi using Antheraea pernyi eggs as substitutive hosts, which are large in size, as clutch size is a parameter of importance to produce high quality parasitoids. Here, we aimed to determine the optimal clutch size for the bisexual Wolbachia-uninfected line (TdB) and Wolbachia-infected thelytokous line (TdT) of T. dendrolimi reared on A. pernyi eggs.

Optimal clutch size for quality control of bisexual and Wolbachia-infected thelytokous lines of Trichogramma dendrolimi Matsumura (Hymenoptera: Trichogrammatidae) mass reared on eggs of a substitutive host, Antheraea pernyi Guérin-Méneville (Lepidoptera: Saturniidae).

Insecticides can have consequences for beneficial arthropods. Insect parasitoids can contact insecticides through direct exposure spray droplets or residues on crop foliage. Here, we focus on better understand the response of Meteorus pulchricornis (Wesmael), a parasitoid wasp of lepidopteran pests, and its detoxification mechanisms on stress caused by phoxim and cypermethrin. Hence, we determined the dose-mortality curves and estimating the sublethal concentrations (LC30 and LC50). Then, we applied the sublethal concentrations against adult parasitoids to assess its survival, parasitism efficacy, and also developmental and morphometric parameters of their offspring. Simultaneously, we check the activities of glutathione S-transferase (GST), acetylcholinesterase (AChE), and peroxidase (POD) after sublethal exposure of both insecticides, which has measured until 48 h after treatment. Overall, phoxim and cypermethrin exhibited acute lethal activity toward the parasitoid with LC50 values 4.608 and 8.570 mg/liter, respectively. Also, we detect that LC30 was able to trigger the enzymatic activity of GST, AChE, and POD, suggesting a potential detoxification mechanism. However, even when subjected to sublethal exposure, our results indicate strong negatives effects, in particular for phoxim, which has affected the parasitism efficacy and also the developmental and morphometric parameters of M. pulchricornis offspring. Therefore, it can be concluded that both phoxim and cypermethrin have negative impacts on M. pulchricornis and we suggest cautioning their use and the need for semifield and field assessments to confirm such an impact.

Evaluation of Sensitivity to Phoxim and Cypermethrin in an Endoparasitoid, Meteorus pulchricornis (Wesmael) (Hymenoptera: Braconidae), and Its Parasitization Efficiency Under Insecticide Stress.

Thelytokous Wolbachia-infected Trichogramma wasps are superior to bisexual uninfected wasps regarding biological control programs. However, continuous oviposition weakens the parthenogenesis-inducing (PI) strength of Wolbachia. Whether this reduced PI strength relates to decreases in the titer of Wolbachia in the ovary and offspring eggs of Trichogramma remains unclear. Here, using fluorescence in situ hybridization (FISH) and reverse transcription quantitative polymerase chain reaction (RT-qPCR) methods, we investigated how the penetrance of Wolbachia-mediated parthenogenesis, Wolbachia density, and distributions of two Wolbachia-infected Trichogramma species, T. pretiosum (TP) and T. dendrolimi (TD), were influenced by different host access treatments [newly-emerged virgin females (NE), 7-day-old females without access to host eggs (NAH), and 7-day-old virgin females with access to host eggs (AH)].

Penetrance during Wolbachia-mediated parthenogenesis of Trichogramma wasps is reduced by continuous oviposition, associated with exhaustion of Wolbachia titers in ovary and offspring eggs.

Horizontal transmission of the endosymbiont, , may occur during superparasitism when parasitoid females deposit a second clutch of eggs on a host.  may increase the superparasitism tendency of Trichogramma wasps by depriving their memory. To test this hypothesis, we investigated the effects of conditioning experience and memory inhibitors (actinomycin D [ACD] and anisomycin [ANI]) on memory capacity, and expressions of memory-related genes ( and ), and superparasitism frequency of -infected (TDW) and uninfected (TD) lines of Trichogramma dendrolimi after conditioning with lemon or peppermint odor. We detected the presence of  in eggs, larvae, pre-pupae, pupae, and adults of Trichogramma by using fluorescence  hybridization. The results showed that TDW females had a more reduced memory capacity than TD females after conditioning. Compared with TD females, TDW females showed a higher proportion of superparasitism and a downregulation of  and  genes after conditioning. TD females fed ACD or ANI showed a higher tendency for superparasitism and a downregulation of  and , along with memory loss after conditioning than TD females fed honey solution only. The presence of  was detected in the anterior region of the larva, pre-pupa, and pupa, but was not found in the head of the adult. The results provide evidence of host behavioral manipulation of  by depriving memory of host Trichogramma wasps based on Poulin' s criteria. These host behavioral changes led by  may be caused by the virulence of  on the nervous system of the host.  The endosymbiotic bacteria, , live widely within cells of arthropods.  are not only transmitted vertically from host mother to offspring, but are also transmitted horizontally among host individuals. Horizontal transmission is expected to occur during superparasitism when host parasitoid females deposit a clutch of eggs on a host previously parasitized by the same parasitoid species. Thus, a question is proposed regarding whether superparasitism behavior is a behavior modification induced by the symbiont to favor symbiont transmission. This study highlights behavioral mechanisms of -induced superparasitism in Trichogramma wasps and the manipulation of symbionts on host parasitoids.

-Driven Memory Loss in a Parasitic Wasp Increases Superparasitism to Enhance Horizontal Transmission.

Wolbachia infection increases the superparasitism frequency of Trichogramma females and provides an opportunity for horizontal intraspecific transmission. However, superparasitism may lead to interstrain competition between Wolbachia-infected Trichogramma offspring and their uninfected counterparts. This study investigated the outcome of interstrain intrinsic competition between Wolbachia-infected thelytokous strain (W) and uninfected bisexual strain (B) of Trichogramma dendrolimi. To determine the developmental rate of both strains, the sizes of immature stages of T. dendrolimi offspring at different times after parasitisation were measured in single parasitism and superparasitism conditions.

Wolbachia-infected Trichogramma dendrolimi is outcompeted by its uninfected counterpart in superparasitism but does not have developmental delay.

The bacterial endosymbiont,  spp. induce thelytokous parthenogenesis in certain parasitoid wasps, such as the egg parasitoid wasps  spp. To complete the cycle of vertical transmission,  displays efficient transovarial transmission by targeting the reproductive tissues and often exhibits strong tissue-specific tropism in their host.

Posterior concentration of  during the early embryogenesis of the host dynamically shapes the tissue tropism of  in host  wasps.

  wasps are egg parasitoids of agricultural lepidopteran pests. The sex of  is determined by its ploidy as well as certain sex ratio distorters, such as the endosymbiotic bacteria  spp. and the paternal sex ratio (PSR) chromosome. The sex determination systems of hymenopterans, such as  spp., involve cascades of the genes  (), - (), and  () and are associated with sex-specific  and  splicing. First, these genes and their sex-specific variants must be identified to elucidate the interactions between the sex ratio disorders and the sex determination mechanism of .  Here, we characterized the sex determination genes , , and  in . Sex-specific  and  variants were detected in cDNA samples obtained from both male and female  wasps. They were observed in the early embryos (1-10 h), late embryos (12-20 h), larvae (32 h and 48 h), pre-pupae (96 h), and pupae (144 h, 168 h, 192 h, and 216 h) of both male and female  offspring.  We detected female-specific  variants throughout the entire early female offspring stage. The male-specific variant began to express at 9-10 h as the egg was not fertilized. However, we did not find any maternally derived, female-specific  variant in the early male embryo. This observation suggests that the female-specific  variant expressed in the female embryo at 1-9 h may not have originated from the maternal female wasp.  The present study might be the first to identify the sex determination genes and sex-specific gene splicing in  wasps. The findings of this study lay the foundation for investigating the sex determination mechanisms of  and other wasps. They also facilitate sex identification in immature  and the application of this important egg parasitoid in biological insect pest control programs.

The identification and expression pattern of the sex determination genes and their sex-specific variants in the egg parasitoid  Matsumura (Hymenoptera: Trichogrammatidae).

In biological control programs, knowledge about diapause regulation in natural enemy insects provides important insight for improving long-term storage, transportation, and field adoption of these biological control agents. As a natural predator of agricultural pests, the lady beetle Coccinella septempunctata has been commercially mass-cultured and widely employed in pest management. In some insects, insulin signaling, in conjunction with the downstream transcription factor Forkhead box O (FoxO), are master regulators of multiple physiological processes involved in diapause, but it is unclear whether insulin signaling and FoxO affect the diapause of C. septempunctata. In this study, we use a combination of approaches to demonstrate that insulin signaling and FoxO mediate the diapause response in C. septempunctata. In diapausing beetles, application of exogenous insulin and knocking down expression of CsFoxo with RNA interference (RNAi) both rescued beetles from developmental arrest. In non-diapausing beetles, knocking down expression of the insulin receptor (CsInR) with RNA interference (RNAi) arrested ovarian development and decreased juvenile hormone (JH) content to levels comparable to the diapause state. Taken together, these results suggest that a shutdown of insulin signaling prompts the activation of the downstream FoxO gene, leading to the diapause phenotype.

Regulation of forkhead box O transcription factor by insulin signaling pathway controls the reproductive diapause of the lady beetle, Coccinella septempunctata.

Article	Year
Gradual, temperature-induced change of secondary sexual characteristics in infected with parthenogenesis-inducing . PeerJ\| PubMed ID: 31497407	2019
Co-occurrence of thelytokous and bisexual Trichogramma dendrolimi Matsumura (Hymenoptera: Trichogrammatidae) in a natural population. Scientific reports\| PubMed ID: 31767914	2019
Effects of temperature and superparasitism on quality and characteristics of thelytokous Wolbachia-infected Trichogramma dendrolimi Matsumura (Hymenoptera: Trichogrammatidae) during mass rea... Scientific reports\| PubMed ID: 31792331	2019
Phylogenetic signals in pest abundance and distribution range of spider mites. BMC evolutionary biology\| PubMed ID: 31805865	2019
Optimal clutch size for quality control of bisexual and Wolbachia-infected thelytokous lines of Trichogramma dendrolimi Matsumura (Hymenoptera: Trichogrammatidae) mass reared on eggs of a su... Pest management science\| PubMed ID: 32112519	2020
Evaluation of Sensitivity to Phoxim and Cypermethrin in an Endoparasitoid, Meteorus pulchricornis (Wesmael) (Hymenoptera: Braconidae), and Its Parasitization Efficiency Under Insecticide Str... Journal of insect science (Online)\| PubMed ID: 33580255	2021
Penetrance during Wolbachia-mediated parthenogenesis of Trichogramma wasps is reduced by continuous oviposition, associated with exhaustion of Wolbachia titers in ovary and offspring eggs. Pest management science\| PubMed ID: 35437949	2022
-Driven Memory Loss in a Parasitic Wasp Increases Superparasitism to Enhance Horizontal Transmission. mBio\| PubMed ID: 36214563	2022
Wolbachia-infected Trichogramma dendrolimi is outcompeted by its uninfected counterpart in superparasitism but does not have developmental delay. Pest management science\| PubMed ID: 36317957	2023
Posterior concentration of during the early embryogenesis of the host dynamically shapes the tissue tropism of in host wasps. Frontiers in cellular and infection microbiology\| PubMed ID: 37424778	2023
The identification and expression pattern of the sex determination genes and their sex-specific variants in the egg parasitoid Matsumura (Hymenoptera: Trichogrammatidae). Frontiers in physiology\| PubMed ID: 37693004	2023
Regulation of forkhead box O transcription factor by insulin signaling pathway controls the reproductive diapause of the lady beetle, Coccinella septempunctata. International journal of biological macromolecules\| PubMed ID: 37977460	2023

Jin-cheng Zhou

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