Phylogeny of the Trichogramma endosymbiont Wolbachia, an alpha-proteobacteria (Rickettsiae)

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

Introduction

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

Method

The present study aimed to describe the basic Wolbachia distribution patterns that occur during the development of Wolbachia-infected, thelytokous Trichogramma dendrolimi, and T. pretiosum. We used fluorescence in situ hybridization (FISH) to investigate Wolbachia signal dynamics during early embryogenesis (from 30 to 120 min). Wolbachia titers and distributions from the embryo to adult stages of Trichogramma after early embryogenesis were detected by absolute quantitative polymerase chain reaction (AQ-PCR) and FISH. The symmetry ratios (SR) of the Wolbachia signals were calculated using the SR odds ratios in the anterior and posterior parts of the host. The SR was determined to describe Wolbachia tropism during early embryogenesis and various developmental stages of Trichogramma.

Results

Wolbachia was concentrated in the posterior part of the embryo during early embryogenesis and the various developmental stages of both T. dendrolimi and T. pretiosum. Wolbachia density increased with the number of nuclei and the initial mitotic division frequency during early embryogenesis. The total Wolbachia titer increased with postembryogenesis development in both T. dendrolimi and T. pretiosum. However, the Wolbachia densities relative to body size were significantly lower at the adult and pupal stages than they were at the embryonic stage.

Discussion

The present work revealed that posterior Wolbachia concentration during early host embryogenesis determined Wolbachia localization in adult wasps. By this mechanism, Wolbachia exhibits efficient vertical transmission across generations by depositing only female Wolbachia-infected offspring. The results of this study describe the dynamics of Wolbachia during the development of their Trichogramma host. The findings of this investigation helped clarify Wolbachia tropism in Trichogramma wasps.

Bacterial Community Survey of Wolbachia-Infected Parthenogenetic Parasitoid Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) Treated with Antibiotics and High Temperature

Wolbachia has been shown to induce thelytokous parthenogenesis in Trichogramma species, which have been widely used as biological control agents around the world. Little is known about the changes of bacterial community after restoring arrhenotokous or bisexual reproduction in the T. pretiosum. Here, we investigate the emergence of males of T. pretiosum through curing experiments (antibiotics and high temperature), crossing experiments, and high-throughput 16S ribosomal RNA sequencing (rRNA-seq). The results of curing experiments showed that both antibiotics and high temperatures could cause the thelytokous T. pretiosum to produce male offspring. Wolbachia was dominant in the thelytokous T. pretiosum bacterial community with 99.01% relative abundance. With the relative abundance of Wolbachia being depleted by antibiotics, the diversity and relative content of other endosymbiotic bacteria increased, and the reproductive mode reverted from thelytoky to arrhenotoky in T. pretiosum. Although antibiotics did not eliminate Wolbachia in T. pretiosum, sulfadiazine showed an advantage in restoring entirely arrhenotokous and successive bisexual reproduction. This study was the first to demonstrate the bacterial communities in parthenogenetic Trichogramma before and after antibiotics or high-temperature treatment. Our findings supported the hypothesis that Wolbachia titer-dependence drives a reproduction switch in T. pretiosum between thelytoky and arrhenotoky.

Selection of Strains of Trichogramma foersteri and Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) for the Control of Palpita forficifera (Lepidoptera: Crambidae)

Palpita forficifera Munroe 1959 is a lepidopteran pest native to the Neotropical region and has been causing damage to olive tree crops in Brazil and Uruguay. The use of egg parasitoids of the genus Trichogramma may be a viable and sustainable alternative to pest management. The objective of the present work was to select species and/or strains of Trichogramma as possible agents of control for P. forficifera. Selections were made from five strains of Trichogramma foersteri Takahashi (R1, R2, R3, R4, and R5) collected in olive orchards of southern Brazil and four strains of Trichogramma pretiosum Riley (AC, PR, MJU, and RVI) from laboratory rearings. The strains of T. foersteri presented the longest periods from egg to adult (≈ 11.5 days) when compared to T. pretiosum (≈ 9.5 days). However, T. foersteri provided, in general, the highest daily percentage of parasitized P. forficifera eggs and, consequently, a higher rate of parasitism (between 50 and 69%) in relation to those of T. pretiosum (variation from 7 to 20%). In addition, T. foersteri provided a higher emergence rate (above 90%), with a sex ratio close to 1.0. However, all strains of T. pretiosum were longer-lived compared to adults of T. foersteri. From the biological parameters evaluated, two distinct groups were formed between T. foersteri and T. pretiosum. In general, T. foersteri has better potential for controlling P. forficifera, demonstrating its potential for use in field multiplication and release programs for the management of the olive larvae.

Effects of Sublethal Concentrations of Tetracycline Hydrochloride on the Biological Characteristics and Wolbachia Titer in Parthenogenesis Trichogramma pretiosum

Simple Summary

Trichogramma pretiosum is an important natural enemy of lepidopteran pests. Wolbachia is an intracellular endosymbiont that induces parthenogenesis in the parasitoid T. pretiosum. Tetracycline antibiotics are widely used to remove endosymbiont Wolbachia from insect hosts. However, the sublethal effects of tetracycline on the development of T. pretiosum and the population dynamic of Wolbachia in T. pretiosum are still unclear. In our present study, after treatment with sublethal concentrations of tetracycline over ten generations, the biological parameters (longevity, parasitized eggs, and fecundity) of treated females and the percentage of female offspring were significantly lower than those in the control. Moreover, the Wolbachia titer in females sharply declined after two generations of antibiotic treatments and decreased to a lower level even after ten successive generations of antibiotic treatments. In addition, the control group with a higher Wolbachia titer produced more female offspring than the tetracycline treatment groups with a lower Wolbachia titer. These results provide new insights into the complex interaction between arthropods and Wolbachia to antibiotic stress.

Abstract

Trichogramma pretiosum Riley is an important natural enemy and biological control agent of lepidopteran pests. Wolbachia is an intracellular endosymbiont that induces parthenogenesis in the parasitoid T. pretiosum. In this paper, the sublethal effects of the antibiotic tetracycline hydrochloride on the development and reproduction of T. pretiosum were studied. Emerged females were fed with sublethal concentrations (LC₅, LC₁₅, and LC₃₅) of tetracycline for ten generations. The biological parameters (longevity, parasitized eggs, and fecundity) of treated females significantly reduced compared with the control Moreover, the percentage of female offspring in the treatments significantly reduced, but the percentage of male offspring significantly increased. In addition, the Wolbachia titer sharply reduced after two generations of antibiotic treatments, but it could still be detected even after ten successive generations of antibiotic treatments, which indicated that Wolbachia was not completely removed by sublethal concentrations of tetracycline. The control lines with higher Wolbachia titers produced more female offspring than the tetracycline treatments with lower Wolbachia titers, indicating that the Wolbachia titer affected the sex determination of T. pretiosum. Our results show that sublethal concentrations of tetracycline had adverse effects on the development of T. pretiosum, and Wolbachia titers affected the sexual development of T. pretiosum eggs.

Yersinia massiliensis (Enterobacteriales: Enterobacteriaceae) in the host Anaphes nitens (Hymenoptera: Mymaridae): first report of association with insects

Endosymbiont bacteria can affect biological parameters and reduce the effectiveness of natural enemies in controlling the target insect. The objective of this work was to identify endosymbiont bacteria in Anaphes nitens (Girault, 1928) (Hymenoptera: Mymaridae), the main natural enemy used to manage Gonipterus platensis (Marelli, 1926) (Coleoptera: Curculionidae). Genomic DNA from six A. nitens populations was extracted and polymerase chain reactions (PCR) were performed with the primers to detect endosymbiont bacteria in this insect. The PCR products were amplified, sequenced, and compared with sequences deposited in the GenBank for the bacteria identification. All A. nitens populations had the bacterium Yersinia massiliensis (Enterobacteriales: Enterobacteriaceae). This bacterium was originally described as free-living, and it is associated with and composes part of the A. nitens microbiota. This is the first report of Y. massiliensis in an insect host.

Comparison of the Micromorphology and Ultrastructure of Pollen Grains of Selected Rubus idaeus L. Cultivars Grown in Commercial Plantation

The genus Rubus is one of the largest taxonomically diverse and complex genera in the family Rosaceae. Morphology of pollen grains (equatorial and polar axes length, shape and size, aperture position, exine sculpture, perforations) is regarded as one of its main diagnostic features for identification of species and varieties. An attempt was made to fill the gap concerning the pollen micromorphology and ultrastructure of R. idaeus L. using light, scanning, and electron transmission microscopy. This study is a comparative analysis of micromorphological and ultrastructural traits of pollen from six raspberry cultivars. The pollen grains were classified as small or medium of shape prolato-spheroids. The parallel striae in the equatorial view in the exine sculpture were sometimes branched dichotomously in ‘Glen Ample’, ‘Polka’, and ‘Polana’, arcuate in ‘Laszka’ and ‘Pokusa’, or irregularly overlapping in ‘Radziejowa’. The width of exine striae of biennial fruiting cultivars was much larger than in repeated fruiting cultivars. In terms of the increasing number of perforations per unit area of the exine surface, the cultivars were ranked as follows: ‘Pokusa’ < ‘Glen Ample’ < ‘Laszka’ < ‘Polka’ < ‘Polana’ < ‘Radziejowa’. The thickest tectum, the highest and thickest columellae with the largest distances between them, and the thicker foot layer were demonstrated in ‘Glen Ample’. The ectoexine constituted on average ca. 78–90% of the exine thickness. The findings may constitute auxiliary traits i.a. for identification of related taxa, interpretation of phylogenetic relationships, and pollination biology.

Gradual, temperature-induced change of secondary sexual characteristics in Trichogramma pretiosum infected with parthenogenesis-inducing Wolbachia

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, Wolbachia-infected Trichogramma pretiosum (T. preW⁺ ) that shows thelytokous parthenogenesis were used as subjects. In order to determine the causes of the T. preW⁺ intersex and the influence of parental generation temperature on gradual changes in secondary masculinization in intersex offspring, we examined the occurrence of intersex offspring (F₁ and F₂ 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 T. preW⁺ parental generation temperature is positively correlated with the probability of intersex offspring. The probability of F₁ intersex is significantly higher than that of F₂ intersex in different high temperature. The degree of secondary masculinization in T. preW⁺ intersexes increases as parental generation temperature increases. In addition, our study first identified 11 intersex types in T. preW⁺ 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: Wolbachia 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 T. preW⁺ intersexes is passed through the parental generation to offspring, and this maternal effect weakens as the number of generations increases. In T. preW⁺ intersex individuals, most exhibit female primary sexual characteristics, and secondary sexual characteristics exhibit signs of masculinization.