Biology subjects

Hoffmann, A. A.

Publications and source records attributed to Hoffmann, A. A..

At least 19 recordsLinked to original sources

bioRxiv2026

Efficacy of 60 personal mosquito repellents and perfumes against Aedes aegypti mosquitoes

Personal insect repellents can offer an effective means of preventing mosquito bites. Despite a wide variety of products that claim to repel mosquitoes, relatively few studies have systematically compared their performance through standardized tests. In Australia, chemical-based repellents must be registered with the Australian Pesticides and Veterinary Medicines Authority (APVMA); however, many unregistered products with unverified effectiveness remain commercially available. Here, we tested 55 insect repellents and 5 non-repellent perfumes and deodorants sold in Australia for their protection against Aedes aegypti mosquito landings (as a proxy for bites) using arm-in-cage assays across eight human subjects. We tested 43 topical repellents (containing 18 different primary active ingredients), four wristbands, three clothing stickers, three ultrasonic devices, one garment, one repellent applied to fabric, two perfumes, two deodorants and one antiperspirant. Thirteen repellents, including all wristbands, stickers and ultrasonic devices did not provide complete protection against mosquito landings for any human subject, while a further sixteen provided complete protection for 1 hr or less on average. Repellents containing DEET, oil of lemon eucalyptus, picaridin and IR3535 as the primary active ingredient were the only products that provided more than 2 hours of complete protection, but with significant variation among products with the same active ingredient. Only 7/30 essential oil-based topical repellents and perfumes provided complete protection for greater than 1 hr. Nearly half (25/52) of the repellents subject to registration with the APVMA were unregistered despite being advertised or labelled as mosquito repellents, and these tended to be less effective than registered products. Only 5/28 repellents met or exceeded their claimed protection time. This study highlights the prevalence of unregistered and ineffective mosquito repellents on the Australian market while providing evidence for products and active ingredients that do protect against mosquito bites under laboratory conditions.

zoology↗

bioRxiv2026

Mosquito fertility is (mostly) resilient to sublethal heat shocks

Insects can experience a loss of fertility under acute heat stress, but impacts vary among species and depend on life stage and sex. We examined the effects of sublethal heat shocks on the fertility of three mosquito species (Aedes aegypti, Aedes notoscriptus and Culex quinquefasciatus) when males or females were exposed at the pupal and adult stages. Reproductive performance was assessed through egg-laying success, fecundity, egg hatchability and viable offspring production. Female heat shock had limited effects on fertility in all three species, though exposure of adult females to 41 {degrees}C for 1 hr reduced viable offspring production in Ae. notoscriptus. Male heat shock reduced egg hatchability in Cx. quinquefasciatus and viable offspring production in Ae. aegypti depending on the life stage exposed. We investigated several other aspects of heat shock exposure on Ae. aegypti fertility. In this species, male fertility partially recovered within 24-48 hours following heat shock exposure, while effects of heat shocks on female fertility occurred regardless of whether heat exposure occurred pre- or post-mating. In addition, maternal heat shock exposure enhanced offspring fecundity and viable offspring production under subsequent sublethal heat stress. Overall, our findings demonstrate that mosquito fertility is largely robust to short-term heat shocks, but there are also complex trait, sex, stage, temporal and species-specific effects, with implications for predicting mosquito population persistence and species persistence under future climate extremes.

zoology↗

bioRxiv2026

Revisiting the diversity of secondary endosymbionts in the major pest oat aphid, Rhopalosiphum padi

There is disagreement on whether secondary endosymbionts are found in the major cereal pest aphid, Rhopalosiphum padi. Some papers report a diversity of secondary bacterial endosymbionts while others have failed to find evidence of these bacteria in this species. Here we revisit this issue by summarizing the relevant literature and through additional sampling of the species in Australia, China and Denmark using a combination of molecular approaches. We find a general absence of secondary endosymbionts beyond the obligate endosymbiont Hamiltonella defensa in R. padi. While the inconsistency in survey results may reflect rapid changes in endosymbiont turnover in populations and/or the impact of ecological factors such as host plant type on endosymbiont diversity, we are concerned that technical issues may be at least partly responsible for inconsistencies in the literature. This leads us to emphasize the importance of multiple sources of evidence required to establish and characterize endosymbiont infections, including PCR and qPCR assays, DNA Sanger sequencing and 16SrRNA gene metabarcoding. We note that several major aphid pests show a low incidence of secondary endosymbionts which raises issues about the importance of these endosymbionts in aphids that constitute pests, even though endosymbionts can in some cases increase host fitness and therefore pest impact.

microbiology↗

bioRxiv2026

Strong reproductive isolation among sympatric lineages of an international mosquito pest

Background: Reproductive isolation describes the degree to which genetic differences among populations reduce the level of neutral gene flow between them. Genomic approaches are currently showing great utility for identifying reproductive isolation between sympatric, morphologically indistinct populations, where hybridisation and introgression may yet be common. Here we use population genomic approaches and a chromosome-level reference assembly to uncover three highly differentiated, cryptic lineages of Aedes notoscriptus, an Australian mosquito disease vector that has invaded New Zealand (c. 1920) and California (c. 2014). Results: We identified a single lineage (Noto1) that was the source of the New Zealand and Californian invasions, and this lineage was also distributed across much of Australia including the Greater Melbourne region where it was sympatric with a second lineage (Noto2). Although Victorian Noto1 and Noto2 were frequently sampled co-locally, hybrids were observed less frequently than expected under random mating, and admixture levels were low, suggestive of selection against hybrids. A bottleneck observed in Victorian Noto1 suggests that Noto1 may have recently expanded its range into the Greater Melbourne region. We also identified a massive structural variant (~25 Mbp; ~10% of chromosome size) in Noto2 that was segregating at intermediate frequencies across the Greater Melbourne region but was fixed in Noto1. Conclusion: Together, these results identify key genetic differences between cryptic lineages of this international disease vector that warrant further investigation given potential differences in vector competence.

evolutionary biology↗

bioRxiv2026

Bridgehead invasions of ambrosia beetles are structured by inbreeding and hybridisation

When invasive populations establish in regions far from their origin, they may accumulate deleterious mutations that limit population viability and later expansion. Invasions stemming from such bridgehead populations may experience further sequential bottlenecks. However, deleterious mutations can be masked or eliminated when populations outbreed with other lineages. Here, we analyse global invasions of a species complex of persistently inbreeding ambrosia beetles, using genomic data (N=247) from invasive populations in Africa, North America and Australia, and from native populations in Asia. We mostly focus on one species of this complex (Euwallacea fornicatus) which poses a severe threat to tree species worldwide and is rapidly expanding its global range. We uncover a single lineage of this species across California, South Africa, and Western Australia, involving an invasive bridgehead and containing almost no nuclear genetic variation. In South Africa we identify a second lineage that has repeatedly hybridised with the first lineage. Genetic patterns in the native range indicate that such opportunistic outbreeding may be common. Despite lacking nuclear variation, the first lineage contained two CO1 haplotypes that were also observed in every hybrid lineage, pointing to heteroplasmy and possible hybrid origins of this lineage. Native populations had fewer missense mutations than invasive populations, indicating that opportunistic outbreeding may help purge fixed deleterious mutations when local lineage diversity is high. These findings highlight the importance of outbreeding even when inbreeding is common, and they demonstrate the biosecurity threat posed by subsequent gene flow into invasive populations.

evolutionary biology↗

bioRxiv2026

Interactions between inbreeding, fitness and the bacterial microbiome in Aedes aegypti mosquitoes

Laboratory and field populations of insects can experience a decline in fitness and loss of genetic diversity due to inbreeding depression and genetic drift, respectively. Matings among related individuals and small population size may also influence insect host microbiomes with consequences for fitness. In the dengue vector mosquito, Aedes aegypti, the bacterial microbiome is largely environmentally determined but recent studies have also revealed host genetic components. We generated a panel of 55 inbred lines from either of two founding outbred populations of Ae. aegypti to test for associations between life history traits, inbreeding, allelic diversity and microbiome composition using ddRADseq and bacterial 16S rRNA gene sequencing on pools of mosquitoes. Effects of inbreeding were diverse with severe composite fitness costs in many lines but minimal costs in others despite similar low levels of genetic diversity. We found no strong relationship between major life history traits across inbred lines, suggesting that any costs due to inbreeding were trait specific. Bacterial microbiome analysis of pooled samples from a subset of populations revealed common microbes across populations, with Elizabethkingia, Aeromonas and Ralstonia being the most abundant. Despite bacterial composition varying widely, there was no clear relationship between microbiome composition and fitness or population origin. However, there were several significant positive correlations between the relative abundance of different microbial taxa across lines. Our results demonstrate diverse impacts of inbreeding on fitness of mosquito populations but with limited impacts on the microbiome.

microbiology↗

bioRxiv2026

Calibrating and documenting host-switching and evolution of incompatibility loci for two closely related Wolbachia clades

Maternally inherited Wolbachia alphaproteobacteria are the most common arthropod endosymbionts. Often Wolbachia spread to high frequencies through cytoplasmic incompatibility, in which cif loci act through sperm to kill embryos lacking Wolbachia. Closely related Wolbachia with diverse cif loci often associate with anciently diverged hosts, but the timescale of associations remains uncertain. We produce new calibrations based on filarial nematodes with vertically inherited Wolbachia that codiverge with their hosts. Applying these calibrations to Wolbachia variants closely related to pathogen-blocking wMel from Drosophila melanogaster, we demonstrate that over a timescale of 1-2 million years, a core set of single-copy Wolbachia loci evolve largely through bifurcation rather than by gene exchange with distant Wolbachia. Dating bifurcating core genomes, we show that "wMel-like" Wolbachia diverged 2.1x105-2.4x106 years inhabit dipteran and hymenopteran hosts diverged more than 108 years. Previous published analysis of variants related to wRi from D. simulans, the first Wolbachia found in a drosophilid, concluded that "wRi-like" Wolbachia spread among different Drosophila in tens of thousands of years. However, our new calibrations suggest these estimates from a mutation-based calibration underestimated wRi-like spread by about a factor of seven. In addition, cif exchanges between wMel-like and wRi-like Wolbachia genomes have occurred over [~]104-106 years. Comparing intact cif loci found in various Wolbachia, we find function-preserving selection in their evolution. We discuss these results in light of theoretical predictions concerning selection on cytoplasmic incompatibility phenotypes within and among host lineages. The wMel variants analyzed may offer new options for Wolbachia-based biocontrol efforts. Article SummaryMaternally transmitted Wolbachia endosymbionts associate with many arthropods. Closely related Wolbachia are known to occupy anciently diverged hosts, but the timescale of associations remains uncertain. Using genomic data from obligate Wolbachia codiverging with filarial nematodes, we calibrate Wolbachia molecular evolution. wMel-like variants that diverged about 104-106 years ago occur in hosts that diverged more than 108 years ago. Incompatibility loci move even more rapidly among these Wolbachia genomes. As these variants diverge, selection occurred on loci involved in both inducing and protecting against cytoplasmic incompatibility. These results elucidate Wolbachia host-range and genome dynamics and provide potential material for applications.

microbiology↗

bioRxiv2025

Heat hardening enhances mosquito heat tolerance in a species-specific and trait-specific manner

Models predict that the distribution of ectotherms including mosquitoes will shift with climate change, but few incorporate adaptive capacity. Acclimation is one mechanism by which mosquitoes could adapt, allowing mosquitoes that have experienced sub-lethal stress previously to tolerate subsequent stressful environments. In this study we evaluated the heat tolerance of three vector mosquito species, Aedes aegypti, Ae. notoscriptus and Culex quinquefasciatus, after being previously exposed to heat hardening. Adult males and females were heat-hardened by exposure to 41{degrees}C for one hour and subsequently tested for heat survival and knockdown following one-hour heat shocks across a range of temperatures up to the lethal limit, ramping CTmax assays and static temperature knockdown time assays. The three species differed markedly in their heat tolerance across all assays, with Ae. aegypti being the most heat tolerant and Cx. quinquefasciatus being the least. Females from all three species were more heat tolerant than males in the one-hour heat shock assays, but effects of sex were absent or inconsistent for CTmax and heat knockdown time assays. A beneficial impact of heat hardening on subsequent heat shock knockdown was evident in both sexes of all three species. However, hardening effects differed substantially for survival 24 hr later, ranging from no effect of hardening in Cx. quinquefasciatus to a [~]1{degrees}C increase in LT50 in Ae. notoscriptus. In contrast, no effects of heat hardening were detected for CTmax or static knockdown time assays. An additional experiment in Ae. aegypti detected no benefits of heat shock exposure in female patents on the thermal tolerance of offspring. Our findings emphasize the need to consider effects of acclimation including heat hardening in models to predict the response of mosquitoes to climate warming. They also have implications for measuring thermal tolerance in mosquitoes more generally, given that both sex and hardening effects depend on the type of assay used and trait measured.

ecology↗

bioRxiv2025

Wolbachia introgression in Rio de Janeiro remains at sub-optimal levels 30 months after its crash: challenges in the sustainability of wMel interventions for dengue control

The deployment of the Wolbachia wMel strain is currently underway in multiple dengue-endemic municipalities across Brazil. The efficacy of this strategy in Rio de Janeiro remains uncertain, primarily due to the difficulty in sustaining high wMel prevalence in regions previously subjected to large-scale releases. A key contributing factor was the routine rotation of insecticides within the framework of Integrated Vector Management (IVM), which led to the use of the larvicide Spinosad for Aedes control in urban areas. This compound was associated with a precipitous decline in Aedes aegypti mosquitoes, regardless the wMel infection status. While wMel-uninfected population recovered within weeks, wMel-infected population remained at low levels likely due to the fitness costs imposed by wMel on egg viability. To assess the long-term persistence of wMel following this demographic collapse, we conducted mosquito sampling across 12 neighborhoods in Rio de Janeiro, 30 months after mosquito populations crashed. Our findings reveal that wMel introgression remains suboptimal, with a mean frequency of 9.87% across the sampled areas. Only two neighborhoods exhibited wMel frequencies exceeding 15%, likely reflecting ongoing localized releases. The reduced prevalence underscores the challenges of achieving self-sustaining wMel establishment in complex urban environments and highlight critical considerations for the implementation of Wolbachia-based dengue control programs in endemic regions. SponsorshipThis study was supported by grants from the CNPq - Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (312282/2022-2, 307209/2023-7) and by FAPERJ - Fundacao Carlos Chagas Filho de Amparo a Pesquisa no Estado do Rio de Janeiro (E-26/211.159/2019, E-26/204.108/2024, E26/2001.844/2017, E-26/210.335/2022, E-26/210.537/2024).

ecology↗

bioRxiv2025

High-throughput chemical toxicity testing for beneficial insects: The value of coated vials

Non-target effects of insecticides used in agriculture can impact the ecosystem services provided by beneficial insects. Understanding the broader effects of chemical usage requires multi-species investigations on the impact of different insecticide active ingredients. In this work, we tested the utility of coated vials as a quick, cheap, and efficient dried residue chemical toxicity assay. This method was compared against dishes sprayed with a Potter tower, which is an industry standard instrument used to apply precise insecticide doses. Our study focused on 2 natural enemies of aphids, larval and adult Hippodamia variegata ladybird beetle, and the parasitoid wasp, Diaeretiella rapae. These natural enemies were exposed to multiple doses of 3 insecticides that are registered for aphid control in Australian agriculture: alpha-cypermethrin (pyrethroid), dimethoate (organophosphate), and sulfoxaflor (sulfoximine). Modelled dose-response relationships showed evidence of general differences in the intercepts between methods, but not in slope (rate of mortality with concentration). However, these subtle statistically significant effects did not translate into marked differences in LC50-values, which were comparable across assay methods for all natural enemies and insecticides tested. Coated vials therefore produced estimates of chemical toxicity that were consistent with those derived from Potter tower sprays. This underscores the validity of coated vials as a method for performing high-throughput chemical toxicity experiments, as required when examining different populations of multiple taxa across a range of insecticide active ingredients.

zoology↗

bioRxiv2025

Populations of the Australian saltmarsh mosquito Aedes vigilax vary between panmixia and temporally stable local genetic structure

Pest management programs can operate more effectively when movement patterns of target species are known. As individual insects are difficult to track, genomic data can instead be used to infer movement patterns based on pest population structure and connectivity. These data can also provide critical information about cryptic taxa relevant to management. Here we present the first genomic investigation of Aedes vigilax, the Australian saltmarsh mosquito, a major arbovirus vector across Australasia. We used a ddRAD pool-seq approach and a draft genome assembly to investigate genetic variation in 60 Ae. vigilax pools from across Australia but with a focus on urban Newcastle and Sydney, NSW. There was strong genetic structure between samples from the west and east coasts of Australia, and additional structure that differentiated east coast populations. Within Newcastle and Sydney, contrasting patterns of genetic structure were evident. In Newcastle, there was no differentiation among subregions up to 60 km apart. In Sydney, samples from one urban subregion were differentiated from others < 3 km apart, and this structure was stable across sampling years. Heterozygosity and Tajimas D indicated no bottlenecks in Newcastle or Sydney populations, suggesting this structure represents a gene flow barrier. Nuclear differentiation patterns contrast with previous mtDNA data indicating two COI clades in the east coast, one of which was also present in Western Australia. The panmixia over 60 km across the Newcastle region corroborates previous field observations of high dispersal capacity in this mosquito. These findings indicate specific challenges that may hinder local suppression strategies for this species.

evolutionary biology↗

bioRxiv2024

Spread of a single superclone drives insecticide resistance in Acyrthosiphon kondoi across an invasive range

Populations under similar selection pressures may adapt via parallel evolution or dispersal of advantageous alleles. Here, we investigated insecticide resistance in the invasive blue-green aphid, Acyrthosiphon kondoi, which reproduces clonally in Australia and has rapidly developed resistance across geographic locations. Using genomic, transcriptomic, and experimental approaches, we explored the evolutionary origins and molecular mechanisms of resistance. We developed the first nuclear genome assembly for A. kondoi (443.8 Mb, 28,405 annotated genes, BUSCO score 97.5%) and a partial mitochondrial assembly (11,598 bp). All resistant strains shared a common ancestor, supporting the spread of a resistant superclone lineage that is distinct from susceptible strains. Resistance was associated with over-expression of an esterase gene that was homologous to E4/FE4 esterases in other aphid pests that are linked to resistance. Functional experiments in Drosophila melanogaster confirmed a causal role of this E4- like esterase in resistance to organophosphates, carbamates, and pyrethroids. These findings highlight how clonal dispersal and insecticide overuse can transform local adaptation into a widespread pest management issue. Our results suggest a parallel macroevolutionary response to insecticide selection in A. kondoi and other aphid species at the gene family level, but with a distinct regulatory mechanism in A. kondoi. Given the rapid spread of the resistant superclone, alternative management strategies, including expanded chemical control options and enhanced biological control, are urgently needed to mitigate this growing pest problem.

evolutionary biology↗

bioRxiv2024

Elevated developmental temperatures below the lethal limit reduce Aedes aegypti fertility

Aedes aegypti mosquitoes are the principal vectors of dengue and continue to pose a threat to human health, with ongoing urbanization, climate change, and trade all impacting the distribution and abundance of this species. Hot periods are becoming increasingly common and their impacts on insect mortality have been well established, but they may have even greater impacts on insect fertility. In this study, we investigated the impacts of high temperatures on Ae. aegypti fertility both within and across generations. Mosquitoes developing under elevated temperatures exhibited higher critical thermal maxima (CTmax) reflecting developmental acclimation, but their fertility declined with increasing developmental temperature. In females, elevated developmental temperatures decreased fecundity while in males it tended to decrease egg hatch proportions and the proportion of individuals producing viable offspring. Rearing both sexes at 35{degrees}C increased fecundity in the subsequent generation but effects of elevated temperatures persisted across gonotrophic cycles within the same generation. Moreover, exposure of adults to 35{degrees}C further decreased fertility beyond the effects of developmental temperature alone. These findings highlight sub-lethal impacts of elevated temperatures on Ae. aegypti fertility and plastic responses to thermal stress within and across generations. This has significant implications for mosquito populations thriving in increasingly warmer environments.

ecology↗

bioRxiv2024

A persistent bacterial Regiella transinfection in the bird cherry-oat aphid Rhopalosiphum padi increasing host fitness and decreasing plant virus transmission

The bird cherry-oat aphid, Rhopalosiphum padi, is a major pest of agriculture due to its ability to directly damage crops and transmit plant viruses. As industries move away from chemical pest control, there is interest in exploring new options to suppress the impact of this pest. Here we describe the production of a transinfected line of R. padi carrying the bacterial endosymbiont, Regiella insecticola, originating from the green peach aphid, Myzus persicae. We show that Regiella increases the fitness of its novel host despite decreasing fitness in its native host. Regiella also shows a low level of horizontal transmission. Importantly the infection suppresses the ability of R. padi to transmit the barley yellow dwarf virus which damages wheat plants. This transinfection could be released to suppress virus transmission by aphids with its ability to persist and spread, making it potentially suitable for wide area release.

microbiology↗

bioRxiv2024

Endosymbionts impact ladybird predation rates of aphids in a temperature-dependent manner

Aphids are worldwide pests causing major economic losses to growers. Current management strategies rely heavily on pesticides, but some effective pesticides are being withdrawn and the efficiency of remaining pesticides is also decreasing as aphids build up resistance. Biological control using predators can provide a sustainable alternative to pesticides under some circumstances, while the deliberate introduction of facultative bacterial endosymbionts that induce host fitness costs and reduce plant virus transmission provides another potential future strategy to combat aphid pests. However, new control options should not be antagonistic, with the concern that the effectiveness of biocontrol might be altered by endosymbiont presence in hosts. We, therefore, tested if predation by two aphidophagous ladybirds, Adalia bipunctata and Harmonia conformis, on the green peach aphid, Myzus persicae, and the oat aphid, Rhopalosiphum padi, was affected by transinfected Rickettsiella viridis and both native and transinfected Regiella insecticola endosymbionts at different temperatures. The predation rate of aphids infected by either endosymbiont was higher at 14 {degrees} C than the rate for uninfected aphids of both species, but the opposite pattern was apparent at 20 {degrees}C and for one host-endosymbiont combination at 26 {degrees}C. Overall, the results showed that higher temperatures increased predation, while differences between intermediate and low temperatures were species-dependent. No transmission of endosymbionts from aphid to ladybird through predation was detected. These findings point to a lack of consistent effects of the investigated endosymbionts on predation rates in these major aphid pests. The temperature dependence of endosymbiont-predation interactions suggests that the impact of seasonal climate should be considered when assessing the potential of endosymbionts in a biological control setting. HIGHLIGHTS- Aphid endosymbiont effects on ladybird predation rates are temperature-dependent - Ladybird predation rate of aphids increases as temperature rises - Prey (aphid) endosymbionts are not transferred to predators (ladybirds)

ecology↗

bioRxiv2024

The endosymbiont Rickettsiella viridis increases the virulence of Diuraphis noxia but reduces alate frequency

Aphids are among the worlds most economically damaging pests and carry a diverse range of bacterial endosymbionts. There is increasing interest in exploring potential applications of natural and novel strains of endosymbionts in aphid control. One endosymbiont, Rickettsiella viridis, has a large fitness cost following transfer from its natural aphid host Acyrthosiphon pisum into a novel host aphid Myzus persicae. Here, we investigated host impacts after transferring the same Rickettsiella strain to an important cereal aphid, the Russian wheat aphid Diuraphis noxia. Rickettsiella in this host resulted in modest fitness effects, with a minor increase in heat tolerance and a decrease in development time at 25{degrees} C. The infection persisted in mixed caged populations under different temperatures. Surprisingly, Rickettsiella increased aphid virulence to wheat plants and to two non-crop hosts of D. noxia, barley grass and brome grass. This was evident from sharper decreases in leaf number and leaf area, as well as an increase in chlorotic streaking when plants were exposed to Rickettsiella-infected D. noxia. Rickettsiella also reduced the proportion of alates in aphids held in small cages and in larger mesocosms containing multiple wheat plants where short-distance dispersal of aphids was impacted. These results provide compelling evidence that Rickettsiella can affect virulence - the first case of an endosymbiont transfer directly influencing aphid virulence to host plants - and highlight the species-specific impacts of endosymbiont transfers on aphids which can involve multiple traits.

microbiology↗

bioRxiv2024

Wolbachia strain wMelM disrupts egg retention by Aedes aegypti females prevented from ovipositing

Aedes aegypti mosquitoes are well adapted to dry climates and can retain their eggs for extended periods in the absence of suitable habitat. Wolbachia strains transferred from other insects to mosquitoes can be released to combat dengue transmission by blocking virus replication and spreading through populations, but host fitness costs imposed by Wolbachia, particularly under some environments, can impede spread. We therefore assessed the impact of two Wolbachia strains being released for dengue control (wAlbB and wMelM) on fecundity and egg viability following extended egg retention (12 or 18 d) under laboratory conditions. Egg viability decreased to a greater extent in females carrying wMelM compared to uninfected or wAlbB females. Fertility fully recovered in uninfected females following a second blood meal after laying retained eggs, while wMelM females experienced only partial recovery. Effects of wMelM on egg retention were similar regardless of whether females were crossed to uninfected or wMelM males, suggesting that fitness costs were triggered by Wolbachia presence in females. The fecundity and hatch proportions of eggs of wMelM females declined with age, regardless of whether females used stored sperm or were recently inseminated. Costs of some Wolbachia strains during egg retention may affect the invasion and persistence of Wolbachia in release sites where larval habitats are scarce and/or intermittent.

ecology↗

bioRxiv2024

Global, asynchronous partial sweeps at multiple insecticide resistance genes in Aedes mosquitoes

Aedes aegypti (yellow fever mosquito) and Ae. albopictus (Asian tiger mosquito) are globally invasive pests that confer the worlds dengue burden. Insecticide-based man-agement has led to the evolution of insecticide resistance in both species, though the genetic architecture and geographical spread of resistance remains incompletely un-derstood. This study investigates partial selective sweeps at resistance genes on two chromosomes and characterises their spread across populations. Sweeps at the volt-age-sensitive sodium channel gene (VSSC) on chromosome 3 correspond to one nu-cleotide substitution in Ae. albopictus and three substitutions in Ae. aegypti, including two at the same nucleotide position (F1534C) that have evolved and spread independently. In Ae. aegypti, we also identified partial sweeps at a second locus on chromosome 2. This locus contained 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 spread of resistance genes globally and are evidence for the critical importance of GST genes in resistance evolution.

evolutionary biology↗