Study on the cytoplasmic incompatibility in some natural population of Culex pipiens complex in China and Japan

The cytoplasmic incompatibility in the field population of Culex pipiens complex from China and Japan was studied. The results of the crossing experiments between 11 different strains suggest that some Japanese strains might be possible to be used for control Chinese strains by using male sterile technique, and the heavy infection of wolbachiae in mosquitoes may have some relations with the cytoplasmic incompatibility in the field population of Cx. pipiens complex.

NDUFA8 potentially rescues Wolbachia-induced cytoplasmic incompatibility in Laodelphax striatellus

The endosymbiont Wolbachia manipulates host reproduction by several strategies, one of the most important of which is cytoplasmic incompatibility (CI). CI can be rescued when Wolbachia-infected males mate with females infected with the same Wolbachia strain. However, the potential rescue mechanism of CI in the small brown planthopper Laodelphax striatellus is unclear. In this study, comparative transcriptome analysis was applied to explore the effect of Wolbachia on L. striatellus eggs. A total of 1387 differentially expressed genes were identified. RNA interference of 7 Wolbachia-upregulated key planthopper genes reduced egg reproduction, suggesting that Wolbachia might improve fecundity in L. striatellus by affecting these 7 genes. Suppressing the expression of another upregulated gene, NDUFA8 (encoding NADH dehydrogenase [ubiquinone] 1 α subcomplex subunit 8-like) by RNA interference significantly increased the mortality of early embryos without affecting the number of deposited eggs. Wolbachia infection upregulated the mRNA level of NDUFA8, and dsNDUFA8 treatment of Wolbachia-infected females recreated CI-like symptoms, suggesting that NDUFA8 is associated with the rescue phenotype. Because all L. striatellus populations worldwide are infected with Wolbachia, NDUFA8 is a potential pest control target.

Intracellular Interactions in the Reproduction Control of Introgressed Strains Involving Species from Drosophila saltans Group(Sophophora Subgenus)with Emphasis to the Effect of Wolbachia Infection

Interspecific hybrids and constructed research models have provided infor-mation on intracellular interactions. We used two introgressed, chromosomally differentiated strains (H4 and H2) derived from F1 hybrids of crosses between D. prosaltans females and D. saltans males. In H4, the D. prosaltans chromosomes were eliminated. In H2, a mixture was maintained, preserving the entire genome of D. prosaltans (except the Y chromosome) and parts of the D. saltans genome. The IIR arm and a segment of chromosome III were eliminated. A third strain, used for comparison, was a normal D. prosaltans strain (P). This study aimed primarily to analyze the effect on the reproductive char-acteristics productivity (number of progeny) and sex-ratio caused by Wolbachia infection in interaction with different chromosome constitutions. For this, infected and uninfected flies were used in intrastrain cross combinations. Firstly, we analyzed the productivity of intracrosses of uninfected parents, in each strain, in order to detect the effects of intracellular interactions, in flies carrying different chromosome constitutions and sharing a Wolbach-ia-free, D. prosaltans cytoplasm. Data indicated that the chromosome parts that were eliminated, in H2, carry the isolating genes that impair productivity in hybrids of the two species, and suggested the occurrence of a nuclear/nuclear interaction. The analysis of Wolbachia-infected flies showed that the three strains presented different responses, depending on the chromosome constitution. As to productivity, the infection was harmful in P strain, in H2 behaved as mutualistic, and, in H4, produced the effect cytoplasmic incompatibility. As to sex-ratio, intracrosses showed significant differences in P and H4 strains. These results, associated with the cytological characteristics of the strains, pointed to the fundamental importance of host chromosome constitution to define the interactive process host/Wolbachia, and showed the flexibility of the endo-symbiont manifested in different forms of self-preservation.

Wolbachia infection dynamics by reaction-diffusion equations

Dengue fever is caused by the dengue virus and transmitted by Aedes mosquitoes.A promising avenue for eradicating the disease is to infect the wild aedes population with the bacterium Wolbachia driven by cytoplasmic incompatibility(CI).When releasing Wolbachia infected mosquitoes for population replacement,it is essential to not ignore the spatial inhomogeneity of wild mosquito distribution.In this paper,we develop a model of reaction-diffusion system to investigate the infection dynamics in natural areas,under the assumptions supported by recent experiments such as perfect maternal transmission and complete CI.We prove non-existence of inhomogeneous steady-states when one of the diffusion coefficients is sufficiently large,and classify local stability for constant steady states.It is seen that diffusion does not change the criteria for the local stabilities.Our major concern is to determine the minimum infection frequency above which Wolbachia can spread into the whole population of mosquitoes.We find that diffusion drives the minimum frequency slightly higher in general.However,the minimum remains zero when Wolbachia infection brings overwhelming fitness benefit.In the special case when the infection does not alter the longevity of mosquitoes but reduces the birth rate by half,diffusion has no impact on the minimum frequency.

Qualitative analysis for a Wolbachia infection model with diffusion

We consider a reaction-diffusion model which describes the spatial Wolbachia spread dynamics for a mixed population of infected and uninfected mosquitoes. By using linearization method, comparison principle and Leray-Schauder degree theory, we investigate the influence of diffusion on the Wolbachia infection dynamics.After identifying the system parameter regions in which diffusion alters the local stability of constant steadystates, we find sufficient conditions under which the system possesses inhomogeneous steady-states. Surprisingly,our mathematical analysis, with the help of numerical simulations, indicates that diffusion is able to lower the threshold value of the infection frequency over which Wolbachia can invade the whole population.

One discrete dynamical model on the Wolbachia infection frequency in mosquito populations

How to prevent and control the outbreak of mosquito-borne diseases,such as malaria,dengue fever and Zika,is an urgent worldwide public health problem.The most conventional method for the control of these diseases is to directly kill mosquitoes by spraying insecticides or removing their breeding sites.However,the traditional method is not effective enough to keep the mosquito density below the epidemic risk threshold.With promising results international,the World Mosquito Program’s Wolbachia method is helping to reduce the occurrence of diseases transmitted by mosquitoes.In this paper,we introduce a generalized discrete model to study the dynamics of the Wolbachia infection frequency in mosquito populations where infected mosquitoes are impulsively released.This generalized model covers all the relevant existing models since 1959 as some special cases.After summarizing known results of discrete models deduced from the generalized one,we put forward some interesting open questions to be further investigated for the periodic impulsive releases.

Global Asymptotic Stability in a Delay Differential Equation Model for Mosquito Population Suppression

A bio-safe dengue control strategy is to use Wolbachia,which can induce incomplete cytoplasmic incompatibility(CI)and reduce the mating competitiveness of infected males.In this work,we formulate a delay differential equation model,including both the larval and adult stages of wild mosquitoes,to assess the impacts of CI intensityξand mating competitivenessθof infected males on the suppression efficiency.Our analysis identifies a CI intensity thresholdξ*below which a successful suppression is impossible.Whenξ≥ξ*,the wild population will be eliminated ultimately if the releasing level exceeds the release amount threshold R*uniformly.The dependence of R*onξandθ,and the impact of temperature on suppression are further exhibited through numerical examples.Our analyses indicate that a slight reduction ofξis more devastating than significantly decrease ofθin the suppression efficiency.To suppress more than 95%wild mosquitoes during the peak season of dengue in Guangzhou,the optimal starting date for releasing is sensitive toξbut almost independent ofθ.One percent reduction ofξfrom 1 requires at least one week earlier in the optimal releasing starting date from 7 weeks ahead of the peak season of dengue.

Experimental evidence of Wolbachia introgressive acquisition between terrestrial isopod subspecies

Wolbachia are the most widespread endosymbiotic bacteria in animals.In many arthropod host species,they manipulate reproduction via several mechanisms that favor their maternal transmission to offspring.Among them,cytoplasmic incompatibility(Cl)promotes the spread of the symbiont by specifically decreasing the fertility of crosses involving infected males and uninfected females,via embryo mortality.These differences in reproductive efficiency may select for the avoidance of incompatible mating,a process called reinforcement,and thus contribute to population divergence.In the terrestrial isopod Porcellio dilatatus,the Wolbachia wPet strain infecting the subspecies P.d.petiti induces unidirectional Cl with uninfected individuals of the subspecies P.d.dilatatus.To study the consequences of Cl on P.d.dilatatus and P.d.petiti hybridization,mitochondrial haplotypes and Wolbachia infection dynamics,we used population cages seeded with different proportions of the 2 subspecies in which we monitored these genetic parameters 5 and 7 years after the initial setup.Analysis of microsatellite markers allowed evaluating the degree of hybridization between individuals of the 2 subspecies.These markers revealed an increase in P.d.dilatatus nuclear genetic signature in all mixed cages,reflecting an asymmetry in hybridization.Hybridization led to the introgressive acquisition of Wolbachia and mitochondrial haplotype from P.d.petiti into nuclear genomes dominated by alleles of P.d.dilatatus.We discuss these results with regards to Wolbachia effects on their host(Cl and putative fitness cost),and to a possible reinforcement that may have led to assortative mating,as possible factors contributing to the observed results.