Cost of Mating and Insemination Capacity of a Genetically Modified Mosquito Aedes aegypti OX513A Compared to Its Wild Type Counterpart

The idea of implementing genetics-based insect control strategies modelled on the traditional SIT is becoming increasingly popular. In this paper we compare a genetically modified line of Aedes aegypti carrying a tetracycline repressible, lethal positive feedback system (OX513A) with its wild type counterpart with respect to their insemination capacities and the cost of courtship and mating. Genetically modified males inseminated just over half as many females as the wild type males during their lifetime. Providing days of rest from mating had no significant effect on the total number of females inseminated by males of either line, but it did increase their longevity. Producing sperm had a low cost in terms of energy investment; the cost of transferring this sperm to a receptive female was much higher. Continued mating attempts with refractory females suggest that males could not identify refractory females before investing substantial energy in courtship. Although over a lifetime OX513A males inseminated fewer females, the number of females inseminated over the first three days, was similar between males of the two lines, suggesting that the identified cost of RIDL may have little impact on the outcome of SIT-based control programmes with frequent releases of the genetically modified males

Transcriptomics and disease vector control

Next-generation sequencing can be used to compare transcriptomes under different conditions. A study in BMC Genomics applies this approach to investigating the effects of exposure to a range of xenobiotics on changes in gene expression in the larvae of Aedes aegypti, the mosquito vector of dengue fever

Dispersal of engineered male Aedes aegypti mosquitoes

BACKGROUND:Aedes aegypti, the principal vector of dengue fever, have been genetically engineered for use in a sterile insect control programme. To improve our understanding of the dispersal ecology of mosquitoes and to inform appropriate release strategies of 'genetically sterile' male Aedes aegypti detailed knowledge of the dispersal ability of the released insects is needed. METHODOLOGY/PRINCIPAL FINDINGS:The dispersal ability of released 'genetically sterile' male Aedes aegypti at a field site in Brazil has been estimated. Dispersal kernels embedded within a generalized linear model framework were used to analyse data collected from three large scale mark release recapture studies. The methodology has been applied to previously published dispersal data to compare the dispersal ability of 'genetically sterile' male Aedes aegypti in contrasting environments. We parameterised dispersal kernels and estimated the mean distance travelled for insects in Brazil: 52.8 m (95% CI: 49.9 m, 56.8 m) and Malaysia: 58.0 m (95% CI: 51.1 m, 71.0 m). CONCLUSIONS/SIGNIFICANCE:Our results provide specific, detailed estimates of the dispersal characteristics of released 'genetically sterile' male Aedes aegypti in the field. The comparative analysis indicates that despite differing environments and recapture rates, key features of the insects' dispersal kernels are conserved across the two studies. The results can be used to inform both risk assessments and release programmes using 'genetically sterile' male Aedes aegypti

The application of self-limiting transgenic insects in managing resistance in experimental metapopulations

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this record.Data sharing: raw data for this study are available as supplementary data files.1. The mass release of transgenic insects carrying female lethal self-limiting genes can reduce pest insect populations. Theoretically, substantial releases can be a novel resistance management tool, since wild type alleles conferring susceptibility to pesticides can dilute resistance alleles in target populations. A potential barrier to the deployment of this technology is the need for large-scale area wide releases. Here we address whether localized releases of transgenic insects could provide an alternative, means of population suppression and resistance management, without serious loss of efficacy. 2. We used experimental mesocosms constituting insect metapopulations to explore the evolution of resistance to the Bacillus thuringiensis toxin Cry1Ac in a high-dose/refugia landscape in the insect Plutella xylostella. We ran two selection experiments, the first compared the efficacy of ‘everywhere’ releases and negative controls to a spatially density-dependent or ‘whack-a-mole’ strategy that concentrated release of transgenic insects in sub-populations with high levels of resistance. The second experiment tested the relative efficacy of whack-a-mole and everywhere releases under spatially homogenous and heterogeneous selection pressure. 3. The whack-a-mole releases were less effective than everywhere releases in terms of slowing the evolution of resistance, which in the first experiment, largely prevented the evolution of resistance. In contrast to predictions, heterogeneous whack-a-mole releases were not more effective under heterogeneous selection pressure. Heterogeneous selection pressure did, however, reduce total insect population sizes 4. Whack-a-mole releases provided early population suppression that was indistinguishable from homogeneous everywhere releases. However, insect population densities tracked the evolution of resistance in this system, as phenotypic resistance provides access to the 90% of experimental diet containing the toxin Cry1Ac. Thus, as resistance levels diverged between treatments, carrying capacities diverged and population sizes increased under the whack- a-mole approach. Synthesis and Applications Spatially density-dependent releases of transgenic insects, particularly those targeting source populations at landscape level, could suppress pest populations in the absence of blanket area-wide management. The resistance management benefits of self-limiting transgenic insects are, however, reduced in spatially localized releases, suggesting that they are not best suited for spatially restricted ‘spot’ treatment of problematic resistance. Nevertheless, area-wide and spatially heterogeneous releases could be used to support other resistance management interventions.This work was supported by the Biotechnology and Biological Sciences Research Council [grant numbers BB/L00948X/1 to MBB and NA, and BB/L00819X/1&2 to BR]

Suppression of a Field Population of Aedes aegypti in Brazil by Sustained Release of Transgenic Male Mosquitoes

The increasing burden of dengue, and the relative failure of traditional vector control programs highlight the need to develop new control methods. SIT using self-limiting genetic technology is one such promising method. A self-limiting strain of Aedes aegypti, OX513A, has already reached the stage of field evaluation. Sustained releases of OX513A Ae. aegypti males led to 80% suppression of a target wild Ae. aegypti population in the Cayman Islands in 2010. Here we describe sustained series of field releases of OX513A Ae. aegypti males in a suburb of Juazeiro, Bahia, Brazil. This study spanned over a year and reduced the local Ae. aegypti population by 95% (95% CI: 92.2%-97.5%) based on adult trap data and 81% (95% CI: 74.9-85.2%) based on ovitrap indices compared to the adjacent no-release control area. The mating competitiveness of the released males (0.031; 95% CI: 0.025-0.036) was similar to that estimated in the Cayman trials (0.059; 95% CI: 0.011-0.210), indicating that environmental and target-strain differences had little impact on the mating success of the OX513A males. We conclude that sustained release of OX513A males may be an effective and widely useful method for suppression of the key dengue vector Ae. aegypti. The observed level of suppression would likely be sufficient to prevent dengue epidemics in the locality tested and other areas with similar or lower transmission

Combining the high-dose/refuge strategy and self-limiting transgenic insects in resistance management - a test in experimental mesocosms

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this record.The high-dose/refuge strategy has been the primary approach for resistance management in transgenic crops engineered with Bacillus thuringiensis toxins. However, there are continuing pressures from growers to reduce the size of Bt toxin-free refugia, which typically suffer higher damage from pests. One complementary approach is to release male transgenic insects with a female-specific self-limiting gene. This technology can reduce population sizes and slow the evolution of resistance by introgressing susceptible genes through males. Theory predicts that it could be used to facilitate smaller refugia or reverse the evolution of resistance. In this study, we used experimental evolution with caged insect populations to investigate the compatibility of the self-limiting system and the high-dose/refuge strategy in mitigating the evolution of resistance in diamondback moth, Plutella xylostella. The benefits of the self-limiting system were clearer at smaller refuge size, particularly when refugia were inadequate to prevent the evolution of resistance. We found that transgenic males in caged mesocosms could suppress population size and delay resistance development with 10% refugia and 4% - 15% initial resistance allele frequency. Fitness costs in hemizygous transgenic insects are particularly important for introgressing susceptible alleles into target populations. Fitness costs of the self-limiting gene in this study (P. xylostella OX4139 line L) were incompletely dominant, and reduced fecundity and male mating competitiveness. The experimental evolution approach used here illustrates some of the benefits and pitfalls of combining mass-release of self-limiting insects and the high dose/refuge strategy, but does indicate that they can be complementary.This work was supported by the Biotechnology and Biological Sciences Research Council [grant numbers BB/L00948X/1 to MBB and NA, and BB/L00819X/1&2 to BR]

Allosteric rescue of catalytically impaired ATP phosphoribosyltransferase variants links protein dynamics to active-site electrostatic preorganisation

Funding: This work was supported by the Biotechnology and Biological Sciences Research Council (BBSRC) [Grant BB/M010996/1] via EASTBIO Doctoral Training Partnership studentships to B. J. R. and G. F., by Stiftelsen Olle Engkvist Byggmästare [Grant 190-0335] and the Knut and Alice Wallenberg Foundation [Grants 2018.0140 and 2019.0431] to S.C.L.K., and by the European Union’s Horizon 2020 Research and Innovation Programme via a Marie Sklodowska-Curie fellowship [Grant 890562] to M.C. The simulations were enabled by resources provided by the Swedish National Infrastructure for Supercomputing (SNIC, UPPMAX), partially funded by the Swedish Research Council [Grant 2016-07213].ATP phosphoribosyltransferase catalyses the first step of histidine biosynthesis and is controlled via a complex allosteric mechanism where the regulatory protein HisZ enhances catalysis by the catalytic protein HisGS while mediating allosteric inhibition by histidine. Activation by HisZ was proposed to position HisGS Arg56 to stabilise departure of the pyrophosphate leaving group. Here we report active-site mutants of HisGS with impaired reaction chemistry which can be allosterically restored by HisZ despite the HisZ:HisGS interface lying ~20 Å away from the active site. MD simulations indicate HisZ binding constrains the dynamics of HisGS to favour a preorganised active site where both Arg56 and Arg32 are poised to stabilise leaving-group departure in WT-HisGS. In the Arg56Ala-HisGS mutant, HisZ modulates Arg32 dynamics so that it can partially compensate for the absence of Arg56. These results illustrate how remote protein-protein interactions translate into catalytic resilience by restoring damaged electrostatic preorganisation at the active site.Publisher PDFPeer reviewe

Analyses of density-dependent effects are needed to understand how and when Wolbachia can control dengue vectors

Releases of Wolbachia-infected mosquitoes have been shown to be an effective method of controlling Aedes aegypti, the main vector of dengue fever, in Australia. A study in BMC Biology from Penelope Hancock and others shows that incorporation of density-dependent effects into population models can provide major improvements in understanding how and when the infected populations can become established

Genetic Elimination of Dengue Vector Mosquitoes

An approach based on mosquitoes carrying a conditional dominant lethal gene (release of insects carrying a dominant lethal, RIDL) is being developed to control the transmission of dengue viruses by vector population suppression. A transgenic strain, designated OX3604C, of the major dengue vector, Aedes aegypti, was engineered to have a repressible female-specific flightless phenotype. This strain circumvents the need for radiation-induced sterilization, allows genetic sexing resulting in male-only releases, and permits the release of eggs instead of adult mosquitoes. OX3604C males introduced weekly into large laboratory cages containing stable target mosquito populations at initial ratios of 8.5-10:1 OX3604C:target eliminated the populations within 10-20 weeks. These data support the further testing of this strain in contained or confined field trials to evaluate mating competitiveness and environmental and other effects. Successful completion of the field trials should facilitate incorporation of this approach into areawide dengue control or elimination efforts as a component of an integrated vector management strategy