Transinfection of buffalo flies (Haematobia irritans exigua) with Wolbachia and effect on host biology

Development of the Incompatible Insect Technique targeting Aedes albopictus: introgression of a wild nuclear background restores the performance of males artificially infected with Wolbachia

The bacterium Wolbachia pipientis is increasingly studied for its potential use in controlling insect vectors or pests due to its ability to induce Cytoplasmic Incompatibility (CI). CI can be exploited by establishing an opportunistic Wolbachia infection in a targeted insect species through trans-infection and then releasing the infected males into the environment as sterilizing agents. Several host life history traits (LHT) have been reported to be negatively affected by artificial Wolbachia infection. Wolbachia is often considered the causative agent of these detrimental effects, and the importance of the host's genetic origins in the outcome of trans-infection is generally overlooked. In this study, we investigated the impact of host genetic background using an Aedes albopictus line recently trans-infected with wPip from the Culex pipiens mosquito, which exhibited some fitness costs. We measured several LHTs including fecundity, egg hatch rate, and male mating competitiveness in the incompatible line after four rounds of introgression aiming at restoring genetic diversity in the nuclear genome. Our results show that introgression with a wild genetic background restored most fitness traits and conferred mating competitiveness comparable to that of wild males. Finally, we show that introgression leads to faster and stronger population suppression under laboratory conditions. Overall, our data support that the host genome plays a decisive role in determining the fitness of Wolbachia-infected incompatible males.IMPORTANCEThe bacterium Wolbachia pipientis is increasingly used to control insect vectors and pests through the Incompatible Insect Technique (IIT) inducing a form of conditional sterility when a Wolbachia-infected male mates with an uninfected or differently infected female. Wolbachia artificial trans-infection has been repeatedly reported to affect mosquitoes LHTs, which may in turn compromise the efficiency of IIT. Using a tiger mosquito (Aedes albopictus) line recently trans-infected with a Wolbachia strain from Culex pipiens and displaying reduced fitness, we show that restoring genetic diversity through introgression significantly mitigated the fitness costs associated with Wolbachia trans-infection. This was further demonstrated through experimental population suppression, showing that introgression is required to achieve mosquito population suppression under laboratory conditions. These findings are significant for the implementation of IIT programs, as an increase in female fecundity and male performance improves mass rearing productivity as well as the sterilizing capacity of released males.

Unique microbial communities of parasitic fleas on wild animals from the Qinghai-Tibet Plateau

Fleas, one of the most significant ectoparasites, play a crucial role as vectors in spreading zoonotic diseases globally. The Qinghai Province, as part of the Qinghai-Tibet Plateau, is one of the provinces in China with the largest number of flea species. In this study, we characterized the microbial communities of eighty-five adult fleas, belonging to nineteen species within four families (Ceratophyllidae, Ctenophthalmidae, Leptopsyllidae, and Pulicidae). We identified a total of 1162 unique operational taxonomic units at the genus level, with flea-borne pathogens such as Wolbachia, Bartonella, Rickettsia being the members of top abundant taxa. Except for comparison between Ctenophthalmidae and Leptopsyllidae families, the analyses of both alpha- and beta- diversity indicators suggested that bacterial diversity varied among flea families. This could be attributed to flea phylogeny, which also influenced by their geographical sites and animal hosts. Results of Linear discriminant analysis effect size (LEfSe) indicated that 29 genera in Ceratophylloidea, 11 genera in Ctenophthalmidae, 15 genera in Leptopsyllidae, and 22 genera in Pulicidae were significantly responsible for explaining the differences among the four flea families (linear discriminant analysis score > 2, P < 0.05). Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt2) analyses showed that the functional pathways varied significantly across flea families, which was supported by the significant correlation between the functional pathways and the microbial communities.

A survey of Wolbachia infection in brachyceran flies from Iran

Wolbachia is a maternally inherited intracellular bacterium that is considered to be the most plentiful endosymbiont found in arthropods. It reproductively manipulates its host to increase the chances of being transmitted to the insect progeny; and it is currently used as a means of suppressing disease vector populations or controlling vector-borne diseases. Studies of the dissemination and prevalence of Wolbachia among its arthropod hosts are important for its possible use as a biological control agent. The molecular identification of Wolbachia relies on different primers sets due to Wolbachia strain variation. Here, we screened for the presence of Wolbachia in a broad range of Brachycera fly species (Diptera), collected from different regions of Iran, using nine genetic markers (wsp, ftsZ, fbpA, gatB, CoxA, gltA, GroEL dnaA, and 16s rRNA), for detecting, assessing the sensitivity of primers for detection, and phylogeny of this bacterium. The overall incidence of Wolbachia among 22 species from six families was 27.3%. The most commonly positive fly species were Pollenia sp. and Hydrotaea armipes. However, the bacterium was not found in the most medically important flies or in potential human disease vectors, including Musca domestica, Sarcophaga spp., Calliphora vicinia, Lucilia sericata, and Chrysomya albiceps. The primer sets of 16s rRNA with 53.0% and gatB with 52.0% were the most sensitive primers for detecting Wolbachia. Blast search, phylogenetic, and MLST analysis of the different locus sequences of Wolbachia show that all the six distantly related fly species likely belonging to supergroup A. Our study showed some primer sets generated false negatives in many of the samples, emphasizing the importance of using different loci in detecting Wolbachia. The study provides the groundwork for future studies of a Wolbachia-based program for control of flies.

wMel Wolbachia alters female post-mating behaviors and physiology in the dengue vector mosquito Aedes aegypti

Globally invasive Aedes aegypti disseminate numerous arboviruses that impact human health. One promising method to control Ae. aegypti populations is transinfection with Wolbachia pipientis, which naturally infects ~40-52% of insects but not Ae. aegypti. Transinfection of Ae. aegypti with the wMel Wolbachia strain induces cytoplasmic incompatibility (CI), allows infected individuals to invade native populations, and inhibits transmission of medically relevant arboviruses by females. Female insects undergo post-mating physiological and behavioral changes-referred to as the female post-mating response (PMR)-required for optimal fertility. PMRs are typically elicited by male seminal fluid proteins (SFPs) transferred with sperm during mating but can be modified by other factors, including microbiome composition. Wolbachia has modest effects on Ae. aegypti fertility, but its influence on other PMRs is unknown. Here, we show that Wolbachia influences female fecundity, fertility, and re-mating incidence and significantly extends the longevity of virgin females. Using proteomic methods to examine the seminal proteome of infected males, we found that Wolbachia moderately affects SFP composition. However, we identified 125 paternally transferred Wolbachia proteins, but the CI factor proteins (Cifs) were not among them. Our findings indicate that Wolbachia infection of Ae. aegypti alters female PMRs, potentially influencing control programs that utilize Wolbachia-infected individuals.

Attempts to use breeding approaches in Aedes aegypti to create lines with distinct and stable relative Wolbachia densities

Wolbachia is an insect endosymbiont being used for biological control in the mosquito Aedes aegypti because it causes cytoplasmic incompatibility (CI) and limits viral replication of dengue, chikungunya, and Zika viruses. While the genetic mechanism of pathogen blocking (PB) is not fully understood, the strength of both CI and PB are positively correlated with Wolbachia densities in the host. Wolbachia densities are determined by a combination of Wolbachia strain and insect genotype, as well as interactions with the environment. We employed both artificial selection and inbreeding with the goal of creating lines of Ae. aegypti with heritable and distinct Wolbachia densities so that we might better dissect the mechanism underlying PB. We were unable to shift the mean relative Wolbachia density in Ae. aegypti lines by either strategy, with relative densities instead tending to cycle over a narrow range. In lieu of this, we used Wolbachia densities in mosquito legs as predictors of relative densities in the remaining individual's carcass. Because we worked with outbred mosquitoes, our findings indicate either a lack of genetic variation in the mosquito for controlling relative density, natural selection against extreme densities, or a predominance of environmental factors affecting densities. Our study reveals that there are moderating forces acting on relative Wolbachia densities that may help to stabilize density phenotypes post field release. We also show a means to accurately bin vector carcasses into high and low categories for non-DNA omics-based studies of Wolbachia-mediated traits.

Cross-tissue and generation predictability of relative Wolbachia densities in the mosquito Aedes aegypti

BACKGROUND

The insect endosymbiotic bacterium Wolbachia is being deployed in field populations of the mosquito Aedes aegypti for biological control. This microbe prevents the replication of human disease-causing viruses inside the vector, including dengue, Zika and chikungunya. Relative Wolbachia densities may in part predict the strength of this 'viral blocking' effect. Additionally, Wolbachia densities may affect the strength of the reproductive manipulations it induces, including cytoplasmic incompatibility (CI), maternal inheritance rates or induced fitness effects in the insect host. High rates of CI and maternal inheritance and low rates of fitness effects are also key to the successful spreading of Wolbachia through vector populations and its successful use in biocontrol. The factors that control Wolbachia densities are not completely understood.

METHODS

We used quantitative PCR-based methods to estimate relative density of the Wolbachia wAlbB strain in both the somatic and reproductive tissues of adult male and female mosquitoes, as well as in eggs. Using correlation analyses, we assessed whether densities in one tissue predict those in others within the same individual, but also across generations.

RESULTS

We found little relationship among the relative Wolbachia densities of different tissues in the same host. The results also show that there was very little relationship between Wolbachia densities in parents and those in offspring, both in the same and different tissues. The one exception was with ovary-egg relationships, where there was a strong positive association. Relative Wolbachia densities in reproductive tissues were always greater than those in the somatic tissues. Additionally, the densities were consistent in females over their lifetime regardless of tissue, whereas they were generally higher and more variable in males, particularly in the testes.

CONCLUSIONS

Our results indicate that either stochastic processes or local tissue-based physiologies are more likely factors dictating Wolbachia densities in Ae. aegypti individuals, rather than shared embryonic environments or heritable genetic effects of the mosquito genome. These findings have implications for understanding how relative Wolbachia densities may evolve and/or be maintained over the long term in Ae. aegypti.

Molecular detection and characterization of the endosymbiont Wolbachia in the European hedgehog flea, Archaeopsylla erinacei

Wolbachia, the endosymbiont of arthropods and onchocercid nematodes is present in many medically important insect species, being also considered for the indirect control of parasitic ones. Archaeopsylla erinacei is a flea species infesting hedgehogs acting as vector of Rickettsia felis, Bartonella henselae, and Rickettsia helvetica, thus having public health relevance. The Wolbachia surface protein (wsp) and 16S rRNA genes were used to determine the presence, prevalence and molecular typing of Wolbachia in this flea species collected in two regions of southern Italy. Of the 45 fleas tested (n = 16 males, 35.6%; n = 29 females, 64.4%), 43 (95.6%; 95% CI: 84.8-99.2) scored positive for Wolbachia, of which 15 (33.3%) and 28 (62.2%) were males and females, respectively. The sex-wise prevalence of this endosymbiont was almost equal in both sexes (males 93.8%; 95% CI: 69.5-99.7; females 96.7%; 95% CI: 83.1-99.8). Single locus sequence analysis (SLST) of Wolbachia revealed two sequence types for 16S rRNA gene, named as wAr_15227 and wAr_15234, which came from two different areas, equally distributed in male and female fleas, whilst only one sequence type was identified for wsp gene. The phylogenetic analysis placed the two 16S rRNA sequence types in paraphyletic clades belonging to the supergroup A and B, respectively. Whilst, the tree of wsp gene clustered the corresponding sequence in the same clade including those of Wolbachia supergroup A. In MLST analyses, both Wolbachia sequence types clustered in a monophyletic clade with Drosophila nikananu (wNik) and Drosophila sturtevanti (wStv) from supergroup A. ClonalFrame analysis revealed a recombination event in the wAr_15234 strain which came from Apulia region. Scientific knowledge of the presence/prevalence of Wolbachia among medically important fleas, may contribute to develop an alternative biological method for the vector control.

Wolbachia: A tool for livestock ectoparasite control

Ectoparasites and livestock-associated insects are a major concern throughout the world because of their economic and welfare impacts. Effective control is challenging and relies mainly on the use of chemical insecticides and acaricides. Wolbachia, an arthropod and nematode-infecting, maternally-transmitted endosymbiont is currently of widespread interest for use in novel strategies for the control of a range of arthropod-vectored human diseases and plant pests but to date has received only limited consideration for use in the control of diseases of veterinary concern. Here, we review the currently available information on Wolbachia in veterinary ectoparasites and disease vectors, consider the feasibility for use of Wolbachia in the control of livestock pests and diseases and highlight critical issues which need further investigation.