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Abstract Background Wolbachia symbiosis in Aedes aegypti is an emerging biocontrol measure against dengue. However, assessing its real-world efficacy is challenging due to the non-randomised, field-based nature of most intervention studies. This research re-evaluates the spatial–temporal impact of Wolbachia interventions on dengue incidence using a large battery of quasi-experimental methods and assesses each method’s validity. Methods A systematic search for Wolbachia intervention data was conducted via PubMed. Efficacy was reassessed using commonly-used quasi-experimental approaches coupled with extensive robustness checks, including geospatial placebo tests and a simulation study. Intervention efficacies across multiple study sites were computed using high-resolution aggregations to examine heterogeneities across sites and study periods. We further designed a stochastic simulation framework to assess the methods’ ability to reproduce true intervention efficacies (IE). Results Wolbachia interventions in Singapore, Malaysia, and Brazil were associated to significant decreases in dengue incidence, with reductions ranging from 48.17% to 69.19%. IEs varied with location and duration. Malaysia showed increasing efficacy over time, while Brazil exhibited initial success with subsequent decline, hinting at operational challenges. Singapore's strategy was highly effective despite partial saturation. Simulations identified Synthetic Control Methods (SCM) and its variant, count Synthetic Control Method (cSCM), as superior in precision, with the smallest percentage errors in efficacy estimation. These methods also demonstrated robustness in placebo tests. Conclusions Wolbachia interventions exhibit consistent protective effects against dengue. SCM and cSCM provided the most precise and robust estimates of IEs, validated across simulated and real-world settings.

Abstract Aedes aegypti (yellow fever mosquito) and Ae. albopictus (Asian tiger mosquito) are globally invasive pests that confer the world’s dengue burden. Insecticide-based management has led to the evolution of insecticide resistance in both species, though the genetic architecture and geographical spread of resistance remains incompletely understood. This study investigates partial selective sweeps at resistance genes on two chromosomes and characterises their spread across populations. Sweeps at the voltage-sensitive sodium channel (VSSC) gene on chromosome 3 correspond to one resistance-associated nucleotide substitution in Ae. albopictus and three in Ae. aegypti, including two substitutions at the same nucleotide position (F1534C) that have evolved and spread independently. In Ae. aegypti, we also identify partial sweeps at a second locus on chromosome 2. This locus contains 15 glutathione S-transferase (GST) epsilon class genes with significant copy number variation among populations and where three distinct genetic backgrounds have spread across the Indo-Pacific region, the Americas, and Australia. Local geographical patterns and linkage networks indicate VSSC and GST backgrounds probably spread at different times and interact locally with different genes to produce resistance phenotypes. These findings highlight the rapid global spread of resistance and are evidence for the critical importance of GST genes in resistance evolution.

ABSTRACT Fertile hybrids can enhance the adaptive capacity and resilience of species under stress by increasing genetic diversity within populations, masking the effects of deleterious recessive alleles, and facilitating the introgression of beneficial genetic variants into parental species. However, many hybrids are infertile. We compared the fertility of aquarium‐reared F1 hybrid and purebred corals of the species Acropora loripes and Acropora kenti and examined the viability of early life stages of second‐generation (F2) hybrid and back‐crossed planula larvae and recruits. The F1 hybrids spawned viable gametes and the F2 hybrid and back‐crossed embryos developed into planula larvae and settled to become sessile coral recruits. The F1 hybrids had greater reproductive fitness than the F1 A. loripes purebred stock in an aquarium environment based on their probability of spawning and their fertilization success in crosses using their gametes. Interspecific coral hybrids can therefore be fertile and have high reproductive fitness, which could benefit the persistence of threatened coral reefs.

Abstract Wolbachia continue to be reported in species previously thought to lack them, particularly Aedes aegypti mosquitoes. The presence of Wolbachia in this arbovirus vector is considered important because releases of mosquitoes with transinfected Wolbachia are being used around the world to suppress pathogen transmission and these efforts depend on a lack of Wolbachia in natural populations of this species. We previously assessed papers reporting Wolbachia in natural populations of Ae. aegypti and found little evidence that seemed convincing. However, since our review, more and more papers are emerging on Wolbachia detections in this species. Our purpose here is to evaluate these papers within the context of criteria we previously established but also new criteria that include the absence of releases of transinfections within the local areas being sampled which has contaminated natural populations in at least one case where novel detections have been reported. We also address the broader issue of Wolbachia detection in other insects where similar issues may arise which can affect overall estimates of this endosymbiont more generally. We note continuing shortcomings in papers purporting to find natural Wolbachia in Ae. aegypti which are applicable to other insects as well.

Abstract Endosymbionts are widespread in arthropods, living in host cells with effects that extend from parasitic to mutualistic. Newly acquired endosymbionts tend to be parasitic, but vertical transmission favors coevolution toward mutualism, with hosts sometimes developing dependency. Endosymbionts negatively affecting host fitness may still spread by impacting host reproductive traits, referred to as reproductive “manipulation,” although costs for hosts are often assumed rather than demonstrated. For cytoplasmic incompatibility (CI) that involves endosymbiont‐mediated embryo death, theory predicts directional shifts away from “manipulation” toward reduced CI strength; moreover, CI‐causing endosymbionts need to increase host fitness to initially spread. In nature, endosymbiont–host interactions and dynamics are complex, often depending on environmental conditions and evolutionary history. We advocate for capturing this complexity through appropriate datasets, rather than relying on terms like “manipulation.” Such imprecision can lead to the misclassification of endosymbionts along the parasitism–mutualism continuum.

As Wolbachia pipientis is more widely being released into field populations of Aedes aegypti for disease control, the ability to select the appropriate strain for differing environments is increasingly important. A previous study revealed that longer-term quiescence in the egg phase reduced the fertility of mosquitoes, especially those harboring the wAlbB Wolbachia strain. This infertility was also associated with a greater biting rate. Here, we attempt to quantify the effect of this heightened biting behavior on the transmission potential of the dengue virus using a combination of assays for fitness, probing behavior, and vector competence, allowing repeat feeding, and incorporate these effects in a model of R0. We show that Wolbachia-infected infertile mosquitoes are more interested in feeding almost immediately after an initial blood meal relative to wild type and Wolbachia-infected fertile mosquitoes and that these differences continue for up to 8 days over the period we measured. As a result, the infertile Wolbachia mosquitoes have higher virus prevalence and loads than Wolbachia-fertile mosquitoes. We saw limited evidence of Wolbachia-mediated blocking in the disseminated tissue (legs) in terms of prevalence but did see reduced viral loads. Using a previously published estimate of the extrinsic incubation period, we demonstrate that the effect of repeat feeding/infertility is insufficient to overcome the effects of Wolbachia-mediated blocking on R0. These estimates are very conservative, however, and we posit that future studies should empirically measure EIP under a repeat feeding model. Our findings echo previous work where periods of extensive egg quiescence affected the reproductive success of Wolbachia-infected Ae. aegypti. Additionally, we show that increased biting behavior in association with this infertility in Wolbachia-infected mosquitoes may drive greater vector competence. These relationships require further exploration, given their ability to affect the success of field releases of Wolbachia for human disease reduction in drier climates where longer egg quiescence periods are expected.

Abstract Wolbachia, one of the most ubiquitous heritable symbionts in lepidopteran insects, can cause mitochondrial introgression in related host species. We recently found mito‐nuclear discordance in the Lepidopteran tribe Tagiadini Mabille 1878 from which Wolbachia has not been reported. In this study, we found that 13 of the 46 species of Tagiadini species tested were positive for Wolbachia. Overall, 14% (15/110) of Tagiadini specimens were infected with Wolbachia and nine new STs were found from 15 isolates. A co‐phylogenetic comparison, divergence time estimation and Wolbachia recombination analysis revealed that mito‐nuclear discordance in Tagiadini species is not mediated by Wolbachia, but Wolbachia acquisition in Tagiadini appears to have occurred mainly through horizontal transmission rather than codivergence.

Abstract Translocation is an increasingly used tool in conservation management, but there is a risk that source populations are overcollected. The risk depends critically on the detection probability and the source population size. We quantified this risk for a wingless grasshopper population in a patch of remnant habitat in suburban Melbourne that was condemned to be cleared for housing development. We collected ∼2000 grasshoppers in five samples spread over 1 month and used the results to estimate the initial population size (∼3400) with high confidence. Despite our perception of substantially depleting the population, we removed only an estimated 60%, and this relatively high fecundity (∼50 eggs per lifetime) annual species had recovered by the following year to near its original density. Wild‐to‐wild translocation is likely to be a low‐cost and effective strategy in the conservation of many invertebrates, and our findings highlight the feasibility of using natural source populations.

Summary: Partial replacement of resident Aedes aegypti mosquitoes with introduced mosquitoes carrying certain strains of inherited Wolbachia symbionts can result in transmission blocking of dengue and other viruses of public health importance. Wolbachia strain wAlbB is an effective transmission blocker and stable at high temperatures, making it particularly suitable for hot tropical climates. Following trial field releases in Malaysia, releases using wAlbB Ae. aegypti have become operationalized by the Malaysian health authorities. We report here on an average reduction in dengue fever of 62.4% (confidence intervals 50–71%) in 20 releases sites when compared to 76 control sites in high-rise residential areas. Importantly the level of dengue reduction increased with Wolbachia frequency, with 75.8% reduction (61–87%) estimated at 100% Wolbachia frequency. These findings indicate large impacts of wAlbB Wolbachia invasions on dengue fever incidence in an operational setting, with incidence expected to further decrease as wider areas are invaded.

The equine South African pointy vector mosquito, Aedes caballus, poses a significant threat to human health due to its capacity for transmitting arboviruses. Despite favorable climate for its existence in southeast Iran, previous records of this species in the area have indicated very low abundance. This comprehensive field and laboratory study aimed to assess its current adult population status in this region, utilizing a combination of ecological, morphological and molecular techniques. Four distinct types of traps were strategically placed in three fixed and two variable mosquito sampling sites in the southern strip of Sistan and Baluchistan Province. Subsequently, DNA was extracted from trapped mosquitoes and subjected to PCR amplification using the molecular markers COI, ITS2, and ANT. In total, 1734 adult Ae. caballus specimens were collected from rural areas, with the majority being captured by CO2-baited bednet traps. A notable increase in the abundance of this species was observed following rainfall in February. The genetic analysis revealed multiple haplotypes based on COI and ITS2 sequences, with COI gene divergence at 0.89%, and ITS2 sequence divergence at 1.6%. This suggests that previous challenges in morphological identification may have led to misidentifications, with many adults previously classified as Ae. vexans potentially being Ae. caballus. The findings of this study hold significant implications for public health authorities, providing valuable insights for integrated and targeted vector control and disease management efforts.

The mosquito Aedes aegypti is distributed worldwide and is recognized as the primary vector for dengue in numerous countries. To investigate whether the fitness cost of a single DENV-1 isolate varies among populations, we selected four Ae. aegypti populations from distinct localities: Australia (AUS), Brazil (BRA), Pakistan (PAK), and Peru (PER). Utilizing simple methodologies, we concurrently assessed survival rates and fecundity. Overall, DENV-1 infection led to a significant decrease in mosquito survival rates, with the exception of the PER population. Furthermore, infected Ae. aegypti from PAK, the population with the lowest infection rate among those tested, exhibited a noteworthy reduction in egg laying. These findings collectively suggest that local mosquito-virus adaptations may influence dengue transmission in endemic settings.

Despite the known benefits of integrated pest management, adoption in Australian broadacre crops has been slow, in part due to the lack of understanding about how pests and natural enemies interact. We use a previously developed process-based model to predict seasonal patterns in the population dynamics of a canola pest, the green peach aphid (Myzus persicae), and an associated common primary parasitic wasp (Diaeretiella rapae), found in this cropping landscape. The model predicted aphid population outbreaks in autumn and spring. Diaeretiella rapae was able to suppress these outbreaks, but only in scenarios with a sufficiently high number of female wasps in the field (a simulated aphid:wasp density ratio of at least 5:1 was required). Model simulations of aphid-specific foliar pesticide applications facilitated biological control. However, a broad-spectrum pesticide negated the control provided by D. rapae, in one case leading to a predicted 15% increase in aphid densities compared to simulations in which no pesticide was applied. Biological and chemical control could therefore be used in combination for the successful management of the aphid while conserving the wasp. This modelling framework provides a versatile tool for further exploring how chemical applications can impact pests and candidate species for biological control.

Background: Dengue remains a global health challenge with limited treatment options, highlighting the need for effective vector control strategies. The introduction of Wolbachia pipientis into Aedes aegypti populations has shown success in reducing dengue transmission across global field trials. However, the spillover effectiveness of the technology on untreated areas is not well-known. This study estimates the spillover protective effectiveness (PE) of Wolbachia-mediated introgression on dengue., Methods: We used the synthetic control method (SCM) under assumption of partial interference to evaluate the direct and spillover PEs of Wolbachia-mediated introgression in a long-running operational trial of the intervention in Malaysia. Synthetic controls (SCs), which comprise of a weighted sum of non-spillover controls, were constructed for each directly-treated and spillover site in the pre-intervention period to account for historical imbalances in dengue risk and risk trajectories. SCs were compared to directly/spillover-treated sites to estimate the impact of Wolbachia-introgression on dengue incidence across each site, calendar year and intervention time. Robustness checks, including visual inspections, root-mean-square error (RMSE) calculations, in-space and in-time placebo checks, and permutation tests, were used to inspect the model's ability in attributing dengue incidence reductions to the Wolbachia interventions., Findings: The direct and spillover PEs of Wolbachia on dengue incidence were expressed as a percentage reduction of dengue incidence, or the absolute case reductions, by comparing SCs to actual intervention/spillover sites. Findings indicate a direct reduction in dengue incidence by 64.35% (95% CI: 63.50-66.71, p < 0.05 using permutation tests) in directly treated areas, corresponding to 1802 (95% CI: 1768-1932) cases averted. Meanwhile, spillover effects contributed to a 37.69% (95% CI: 36.45-38.49, p < 0.05) reduction in adjacent non-intervention areas, accounting for 115 (95% CI: 104-132) absolute cases averted. Tracking PEs by intervention time revealed a dose-response relationship, where PEs increased concomitantly with Wolbachia frequency. Model checks confirmed the robustness of these results, and ascertained that these PEs were not an artefact of poor control selection, pre-trends in dengue incidence or poor predictive ability of the fitted SCs., Interpretation: Wolbachia-introgression effectively diminished dengue incidence in directly-treated and surrounding spillover regions. This dual effectiveness highlights the potential of Wolbachia-infected mosquitoes as a sustainable, cost-effective strategy against dengue., Funding: This research is hosted by CNRS@CREATE and supported by the National Research Foundation, Prime Minister's Office, Singapore, under its Campus for Research Excellence and Technological Enterprise (CREATE) program, and is funded by the Lee Kong Chian School of Medicine-Ministry of Education Start-Up Grant. The original Hoffmann et al. (2024) study was funded by the Wellcome Trust Awards 226166, 108508, 202888 and the Ministry of Health Malaysia NMRR-16-297-28898., Competing Interests: Declaration of interests We declare no competing interests., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Understanding the genetic basis of local adaptation in thermal performance is useful for predicting species distribution shifts under anthropogenic climate change. Many species are distributed across multiple biogeographic regions, and the uniquely adapted populations in each region may respond to future ocean warming with distinct distribution changes. In the present study, we investigated phylogeographic patterns, thermal sensitivity, and genetic differentiation in the intertidal snail Littorina brevicula along China's coast. Whole-genome sequencing results based on a newly assembled chromosome-level genome revealed two genetic lineages, with a north-south divergence that is linked to the thermal environment. Within each lineage, individuals could be further subdivided into genetic subgroups that differ at key genomic loci underpinning differences in upper heat tolerance. Heat stress drives adaptive divergence across multiple levels of organization, from the individual to the biogeographic level. Taking into account genetic diversity associated with variation in heat tolerance, a physiological species distribution model (pSDM) was applied to predict the distributions of the different genetic subgroups in response to climate change. Both northern and southern lineages were predicted to experience declines in habitat suitability under a 4°C future warming scenario, and that a genotypic subset of snails from the southern lineage may even be driven to extinction. These findings illustrate that even when a species' range is maintained, it can nonetheless experience a significant decrease in adaptive diversity as a result of climate change. The integrated approach presented here, which considered both physiological and adaptive genetic variation at the level of individuals within a biogeographical context, provided new insights into how marine species can respond to global warming., (© 2024 John Wiley & Sons Ltd.)

Mosquito-borne diseases, such as dengue and malaria, pose a significant burden to global health. Current control strategies with insecticides are only moderately effective. Scalable solutions are needed to reduce the transmission risk of these diseases. Symbionts and genome engineering-based mosquito control strategies have been proposed to address these problems. Bacterial, fungal, and viral symbionts affect mosquito reproduction, reduce mosquito lifespan, and block pathogen transmission. Field tests of endosymbiont Wolbachia -based methods have yielded promising results, but there are hurdles to overcome due to the large-scale rearing and accurate sex sorting required for Wolbachia -based suppression approaches and the ecological impediments to Wolbachia invasion in replacement approaches. Genome engineering-based methods, in which mosquitoes are genetically altered for the modification or suppression of wild populations, offer an additional approach for control of mosquito-borne diseases. In particular, the use of gene drive alleles that bias inheritance in their favor is a potentially powerful approach. Several drives are frequency dependent, potentially giving them broadly similar population dynamics to Wolbachia . However, public acceptance and the behavior of released drives in natural mosquito populations remain challenges. We summarize the latest developments and discuss the knowledge gaps in both symbiont- and gene drive-based methods.

Background: Wolbachia are widespread intracellular bacteria in insects that often have high rates of spread due to their impact on insect reproduction. These bacteria may also affect the mating behavior of their host with impacts on the fitness of host progeny. In this study, we investigated the impact of Wolbachia on a preference for mating with young or old males in the parasitoid wasp Habrobracon hebetor., Results: Our results showed that uninfected females from a tetracycline-treated line preferred to mate with young males, whereas Wolbachia-infected females had no preference. Time to mating was relatively shorter in the infected lines. Regardless of Wolbachia infection status, progeny resulting from matings with young males showed higher fitness than those from crosses with old males, and infected females crossed with infected young males showed the highest performance., Conclusion: These results suggest an impact of Wolbachia on female mate preference and offspring fitness although it is unclear how this phenomenon increases Wolbachia transmission of infected wasps. © 2024 Society of Chemical Industry., (© 2024 Society of Chemical Industry.)

Aphids (Hemiptera: Aphidoidea) are economically important crop pests worldwide. Because of growing issues with insecticide resistance and environmental contamination by insecticides, alternate methods are being explored to provide aphid control. Aphids contain endosymbiotic bacteria that affect host fitness and could be targeted as potential biocontrol agents, but such novel strategies should not impact the effectiveness of traditional chemical control. In this work, we used a novel endosymbiont transinfection to examine the impact of the endosymbiont Rickettsiella viridis on chemical tolerance in 3 important agricultural pest species of aphid: Myzus persicae (Sulzer) (Hemiptera: Aphididae), Rhopalosiphum padi (Linnaeus) (Hemiptera: Aphididae), and Diuraphis noxia (Mordvilko ex Kurdjumov) (Hemiptera: Aphididae). We tested tolerance to the commonly used insecticides alpha-cypermethrin, bifenthrin, and pirimicarb using a leaf-dip bioassay. We found no observed effect of this novel endosymbiont transinfection on chemical tolerance, suggesting that the strain of Rickettsiella tested here could be used as a biocontrol agent without affecting sensitivity to insecticides. This may allow Rickettsiella transinfections to be used in combination with chemical applications for pest control. The impacts of other endosymbionts on insecticide tolerance should be considered, along with tests on multiple aphid clones with different inherent levels of chemical tolerance., (© The Author(s) 2024. Published by Oxford University Press on behalf of Entomological Society of America.)

Two Wolbachia strains, w Mel and w AlbB, have been transinfected into Aedes aegypti mosquitoes for population replacement with the aim of reducing dengue transmission. Epidemiological data from various endemic sites suggest a pronounced decrease in dengue transmission after implementing this strategy. In this study, we investigated the impact of the Wolbachia strains w Mel and w AlbB on Ae. aegypti fitness in a common genetic background. We found that Ae. aegypti females infected with the w Mel strain exhibited several significant differences compared with those infected with the w AlbB strain. Specifically, w Mel-infected females laid significantly fewer eggs, ingested a lower amount of blood, had a reduced egg production rate, and exhibited a decreased Wolbachia density at a later age compared with mosquitoes infected with the w AlbB strain. Conversely, the w AlbB strain showed only mild negative effects when compared with Wolbachia -uninfected specimens. These differential effects on Ae. aegypti fitness following infection with either w Mel or w AlbB may have important implications for the success of population replacement strategies in invading native Ae. aegypti populations in endemic settings. Further research is needed to better understand the underlying mechanisms responsible for these differences in fitness effects and their potential impact on the long-term efficacy of Wolbachia -based dengue control programs.IMPORTANCEThe transmission of arboviruses such as dengue, Zika, and chikungunya is on the rise globally. Among the most promising strategies to reduce arbovirus burden is the release of one out of two strains of Wolbachia -infected Aedes aegypti : w Mel and w AlbB. One critical aspect of whether this approach will succeed involves the fitness cost of either Wolbachia strains on mosquito life history traits. For instance, we found that w Mel-infected Ae. aegypti females laid significantly fewer eggs, ingested a lower amount of blood, had a reduced egg production rate, and exhibited a decreased Wolbachia density at a later age compared with mosquitoes infected with the w AlbB strain. Conversely, the w AlbB strain showed only mild negative effects when compared with Wolbachia -uninfected specimens. These differential effects on mosquito fitness following infection with either w Mel or w AlbB may have important implications for the success of population replacement strategies in invading native Ae. aegypti populations., Competing Interests: The authors declare no conflict of interest.