Biology subjects

Hoffmann, A. A.

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

At least 37 records · Page 2Linked to original sources

bioRxiv2024

Acute toxicity effects of pesticides on beneficial organisms - Dispelling myths for a more sustainable use of chemicals in agricultural environments

Agricultural practitioners, researchers and policymakers are increasingly advocating for integrated pest management (IPM) to reduce pesticide use while preserving crop productivity and profitability. Selective pesticides, putatively designed to act on pests while minimising impacts on off-target organisms, have emerged as one such option - yet evidence of whether these compounds control pests without adversely affecting natural enemies and other beneficial species (henceforth beneficials) remains scarce. At present, the selection of pesticides compatible with IPM often considers a single (or a limited number of) widely distributed beneficial species, without considering undesired effects on co-occurring beneficials. In this study, we conducted standardised laboratory bioassays to assess the acute toxicity effects of 20 chemicals on 15 beneficial species at multiple exposure timepoints, with the specific aims to: (1) identify common and diverging patterns in acute toxicity responses of tested beneficials; (2) determine if the effect of pesticides on beetles, wasps and mites is consistent across species within these groups; and (3) assess the impact of mortality assessment timepoints on International Organisation for Biological Control (IOBC) toxicity classifications. Our work demonstrates that in most cases, chemical toxicities cannot be generalised across a range of beneficial insects and mites providing biological control, a finding that was found even when comparing impacts among closely related species of beetles, wasps and mites. Additionally, we show that toxicity impacts increase with exposure length, pointing to limitations of IOBC protocols. This work challenges the notion that chemical toxicities can be adequately tested on a limited number of representative species; instead it highlights the need for careful consideration and testing on a range of regionally and seasonally relevant beneficial species.

pharmacology and toxicology↗

bioRxiv2024

Hormetic effect induced by Beauveria bassiana in Myzus persicae

Myzus persicae, a serious sap-sucking pest of a large variety of host plants in agriculture, is traditionally controlled using chemical insecticides but there is interest in using biopesticides as restrictions are increasingly placed on the use of broad-spectrum pesticides. Here we show that in petri dish experiments high concentrations of the fungal entomopathogen Beauveria bassiana (strain PRRI 5336) lead to rapid mortality of M. persicae but at a low concentration (1 x 104 conidia mL-1) there is a hormetic effect where longevity and fecundity are enhanced. Hormetic effects persisted across a generation with reduced development times and increased fecundity in the offspring of M. persicae exposed to B. bassiana. Whole plant experiments point to a hormetic effect being detected in two out of three tested lines. The impact of these effects might also depend on whether M. persicae was transinfected with the endosymbiont Rickettsiella viridis, which decreases fecundity and survival compared to aphids lacking this endosymbiont. This fecundity cost was ameliorated in the generation following exposure to the entomopathogen. While B. bassiana is effective in controlling M. persicae especially at higher spore concentrations, utilization of this entomopathogen requires careful consideration of hormetic effects at lower spore concentrations, and further research to optimize its application for sustainable agriculture is recommended. AUTHOR SUMMARYBiopesticides such as Beauveria bassiana can be effective alternatives to chemical insecticides to control insect pests. We tested the efficacy of this biopesticide against the important agricultural pest aphid Myzus persicae in laboratory experiments. We also tested whether the potential biological control agent and endosymbiont Rickettsiella viridis could provide protection against mortality caused by B. bassiana. While high doses of B. bassiana caused rapid mortality in aphids, low doses enhanced aphid fecundity and survival. This enhancement persisted into the next generation, with shortened development times and increased fecundity regardless, even when high doses were used in the previous generation. The endosymbiont R. viridis did not provide clear protection against B. bassiana, in contrast to previous studies in other aphid species, but beneficial effects at low doses also occurred in this aphid line. We also observed hormesis on experiments on whole plants, but only for some aphid genotypes. To a lesser extent, we also observed beneficial effects of low doses of B. bassiana in experiments on whole plants, but only in some aphid genotypes. Fitness enhancement by biopesticides at low doses raises concerns for field applications but further research is required to understand its underlying mechanisms.

ecology↗

bioRxiv2023

Rapid turnover of pathogen-blocking Wolbachia and their incompatibility loci

About half of all insect species carry maternally inherited Wolbachia alphaproteobacteria, making Wolbachia the most common endosymbionts known in nature. Often Wolbachia spread to high frequencies within populations due to cytoplasmic incompatibility (CI), a Wolbachia-induced sperm modification caused by prophage-associated genes (cifs) that kill embryos without Wolbachia. Several Wolbachia variants also block viruses, including wMel from Drosophila melanogaster when transinfected into the mosquito Aedes aegypti. CI enables the establishment and stable maintenance of pathogen-blocking wMel in natural Ae. aegypti populations. These transinfections are reducing dengue disease incidence on multiple continents. While it has long been known that closely related Wolbachia occupy distantly related hosts, the timing of Wolbachia host switching and molecular evolution has not been widely quantified. We provide a new, conservative calibration for Wolbachia chronograms based on examples of co-divergence of Wolbachia and their insect hosts. Synthesizing publicly available and new genomic data, we use our calibration to demonstrate that wMel-like variants separated by only about 370,000 years have naturally colonized holometabolous dipteran and hymenopteran insects that diverged approximately 350 million years ago. Data from Wolbachia variants closely related to those currently dominant in D. melanogaster and D. simulans illustrate that cifs are rapidly acquired and lost among Wolbachia genomes, on a time scale of 104-105 years. This turnover occurs with and without the Wovirus prophages that contain them, with closely related cifs found in distantly related phages and distantly related cifs found in closely related phages. We present evidence for purifying selection on CI rescue function and on particular Cif protein domains. Our results quantify the tempo and mode of rapid host switching and horizontal gene transfer that underlie the spread and diversity of Wolbachia sampled from diverse host species. The wMel variants we highlight from hosts in different climates may offer new options for broadening Wolbachia-based biocontrol of diseases and pests.

evolutionary biology↗

bioRxiv2023

'Drifting' Buchnera genomes track the microevolutionary trajectories of their aphid hosts

Evolution of Buchnera-aphid host symbioses is often studied among species at macroevolutionary scales. Investigations within species offer a different perspective about how eco-evolutionary processes shape patterns of genetic variation at microevolutionary scales. Our study leverages new and publicly available whole-genome sequencing data to study Buchnera-aphid host evolution in Myzus persicae, the peach potato aphid, a globally invasive and polyphagous pest. Across 43 different asexual, clonally reproducing isofemale strains, we examined patterns of genomic covariation between Buchnera and their aphid host and considered the distribution of mutations in protein-coding regions of the Buchnera genome. We found Buchnera polymorphisms within aphid strains, suggesting the presence of genetically different Buchnera strains within the same clonal lineage. Genetic distance between pairs of Buchnera samples was positively correlated to genetic distance between their aphid hosts, indicating shared evolutionary histories. However, there was no segregation in the genetic variation of both M. persicae and Buchnera with plant host (Brassicaceae and non-tobacco Solanaceae) and no associations between genetic and geographic distance at global or regional spatial scales. Abundance patterns of non-synonymous mutations were similar to synonymous mutations in the Buchnera genome, and both mutation classes had similar site frequency spectra. We hypothesize that a predominance of neutral processes results in the Buchnera of M. persicae to simply drift with the evolutionary trajectory of their aphid hosts. Our study presents a unique microevolutionary characterisation of Buchnera-aphid host genomic covariation across multiple aphid clones. This provides a new perspective on the eco-evolutionary processes generating and maintaining polymorphisms in a major pest aphid species and its obligate primary endosymbiont.

evolutionary biology↗

bioRxiv2023

Acute toxicity effects of pesticides on predatory snout mites (family Bdellidae)

Predatory mites biologically control a range of arthropod crop pests and are often central to agricultural IPM strategies globally. Conflict between chemical and biological pest control has prompted increasing interest in selective pesticides with fewer off-target impacts on beneficial invertebrates, including predatory mites. However, the range of predatory mite species included in standardised pesticide toxicity assessments does not match the diversity of naturally-occurring species contributing to biocontrol, with most testing carried out on species from the family Phytoseiidae. Here, we aim to bridge this knowledge gap by investigating the impacts of 22 agricultural pesticides on the predatory snout mite Odontoscirus lapidaria (Kramer) (family Bdellidae). Using internationally standardised testing methodologies, we identified several active ingredients with minimal impact on O. lapidaria mortality, including Bacillus thuringiensis, nuclear polyhedrosis virus, flonicamid, afidopyropen, chlorantraniliprole and cyantraniliprole, which may therefore be good candidates for IPM strategies utilising both chemical and biological control. Importantly, we reveal differences between Bdellidae and Phytoseiidae in responses to a number of chemicals, including the miticides diafenthiuron and abamectin, highlighting the risk of making generalisations around acute toxicity based on tests with one beneficial mite family. We also explored the impacts of several pesticides on a second Bdellidae species and found differences in the response to chlorpyrifos compared with O. lapidaria, further highlighting the taxon-specific nature of non-target toxicity effects.

pharmacology and toxicology↗

bioRxiv2023

Restoring declining species through translocations: A test case using flightless grasshoppers in an urban setting

O_LIPopulation translocations are used increasingly as a conservation strategy for vertebrates. However, relatively few attempts have been made to translocate invertebrates despite their potential benefits for food webs, and despite the practicality of undertaking such translocations in small areas including urban environments where space is limited. C_LIO_LIWe conducted 36 translocations of 1851 individuals of the generalist flightless grasshopper Vandiemenella viatica across urban Melbourne, where 93% of its original habitat has been lost. C_LIO_LIWe aimed to understand characteristics essential for grasshopper persistence and to investigate detection, occupancy, dispersal, and habitat suitability throughout its active period to improve insect translocation success in urban settings using revegetated sites and small remnant habitats. We also measured movement and detection probability after one week in short-term trials. C_LIO_LIThe one-week trial indicated that grasshopper sex and colour morph did not influence the probability of detection, and there was no evidence of directional movement by females and males. C_LIO_LIOne year after translocation, V. viatica were found in 28 out of 36 translocation sites. These surveys showed that detection probability changed across survey seasons and was influenced by soil temperature. Also, soil temperature positively affected detection in the winter surveys. Occupancy probability was influenced by graminoid cover, plant species richness and weed cover. We found no evidence of directional movement by females and males in the F1 generation. Abundance and presence/absence data were best explained by graminoid cover and plant species richness. C_LIO_LIOur findings suggest that wingless grasshopper translocations are feasible in small urban patches of suitable habitat, helping to restore invertebrate biodiversity and ecological services. C_LI

ecology↗

bioRxiv2023

A transmission chain linking Mycobacterium ulcerans with Aedes notoscriptus mosquitoes, possums and human Buruli ulcer cases in southeastern Australia

In temperate southeastern Australia over the past two decades there has been a marked progressive increase in human cases of Buruli ulcer, an infection of subcutaneous tissue caused by Mycobacterium ulcerans. Native possums are the major local environmental reservoir of M. ulcerans as they not only develop Buruli lesions but they also shed M. ulcerans in their excreta. However the way humans acquire M. ulcerans from possums has not been determined. Previous case-control studies, insect field surveys and vector competence studies have suggested a role for mosquitoes in M. ulcerans transmission between possums and humans. To explore these links we conducted an extensive, 4-month structured mosquito field survey and four ad hoc field surveys across an area of 350km2 on the Mornington Peninsula, an area endemic for Buruli ulcer to the south of the major metropolitan city of Melbourne. We then compared spatial and temporal patterns of M. ulcerans-positive mosquito occurrence with M. ulcerans-positive possums (established by previous possum excreta surveys) and human Buruli ulcer cases across the region. We used metabarcoding to assess mosquito blood-feeding host preference and to reconstruct M. ulcerans genomes from positive mosquitoes to test epidemiological inferences. We collected 66,325 mosquitoes spanning 26 different species from 180 repeatedly sampled traps over a 4-month period. Culex molestus and Aedes notoscriptus were the dominant species (42% and 35% of trapped mosquitoes, respectively). PCR screening 25% of trapped mosquitoes revealed a significant association between M. ulcerans and Ae. notoscriptus (p<0.0001) with a maximum likelihood estimate (MLE) of 5.88 M. ulcerans positive mosquitoes per 1,000 tested. Using spatial scanning statistics, we also observed significant overlap between clusters of M. ulcerans-positive Ae. notoscriptus, M. ulcerans-positive possum excreta and human Buruli ulcer cases. Metabarcoding analyses of blood-fed Ae. notoscriptus showed individual mosquitoes had fed both on humans and native possums. Enrichment genome sequencing from PCR-positive mosquitoes confirmed shared M. ulcerans genome single-nucleotide polymorphism (SNP) profiles between mosquitoes, possum excreta and clinical human isolates within the same regions. These findings indicate that Ae. notoscriptus likely transmit M. ulcerans in southeastern Australia and highlight mosquito control as a plausible means to control the Buruli ulcer epidemic in our region.

microbiology↗

bioRxiv2023

Evaluation of In2Care mosquito stations for suppression of the Australian backyard mosquito, Aedes notoscriptus

Aedes notoscriptus (Skuse) is a container-inhabiting mosquito endemic to Australia that vectors arboviruses and is suspected to transmit Mycobacterium ulcerans, the cause of Buruli ulcer. We evaluated the effectiveness of the In2Care(R) station, which suppresses mosquito populations via the entomopathogenic fungus, Beauveria bassiana, and the insect growth regulator pyriproxyfen, the latter of which is autodisseminated among larval habitats by contaminated mosquitoes. A field trial was conducted using 110 In2Care(R) stations in a 50,000 m2 area and results were compared to four control areas that did not receive the treatment. Efficacy was evaluated by comparing egg counts and measuring larvicidal impact in surrounding breeding sites. Laboratory experiments validated the effect of B. bassiana on adult survival. Results of this field trial indicate that, six weeks after the In2Care(R) stations were deployed, treatment site ovitraps contained 43% fewer eggs than control site ovitraps, and 33% fewer eggs after ten weeks, suggesting that the In2Care(R) station was able to reduce the egg density of Ae. notoscriptus. Population reduction remained evident for up to three weeks after In2Care(R) stations were removed. Treatment site ovitraps had significantly fewer Ae. notoscriptus eclosing than control site ovitraps, confirming the pyriproxyfen autodissemination feature of the stations. An average reduction of 50% in adult eclosion was achieved. Exposure to B. bassiana resulted in four-times higher mortality among adult mosquitoes. Additionally, using fresh In2Care(R) nettings led to an 88% decrease in average survival compared to four-week-old nettings. The use of In2Care(R) stations has potential for suppressing Ae. notoscriptus egg density.

ecology↗

bioRxiv2023

How often are male mosquitoes attracted to humans?

Many mosquito species live close to humans where females feed on human blood. While male mosquitoes do not feed on blood, it has long been recognized that males of some species can be attracted to human hosts. To investigate the frequency of male mosquito attraction to humans, we conducted a literature review and human-baited field trials, as well as laboratory experiments involving males and females of three common Aedes species. Our literature review indicated that male attraction to humans is limited to a small number of species, including Ae. aegypti and Ae. albopictus. In our human-baited field collections, only 4 out of 13 species captured included males. In laboratory experiments, we found that male Ae. notoscriptus and Ae. vigilax showed no attraction to humans, while male Ae. aegypti exhibited persistent attraction for up to 30 minutes. Both male and female Ae. aegypti displayed similar preferences for different human subjects, suggesting that male Ae. aegypti respond to similar cues as females. Additionally, we found that mosquito repellents applied to human skin effectively repelled male mosquitoes. These findings shed light on mosquito behaviour and have implications for mosquito control programs, particularly those involving the release or monitoring of the male mosquito population.

animal behavior and cognition↗

bioRxiv2022

Evolution of an acetylcholinesterase gene complex and its contribution to organophosphate insensitivity in an invasive mite pest

BACKGROUNDInvasive Australian populations of redlegged earth mite, Halotydeus destructor (Tucker), are evolving increasing organophosphate resistance. In addition to the canonical ace gene, the target gene of organophosphates, the H. destructor genome contains many radiated ace-like genes that vary in copy number and amino acid sequence. In this work, we characterise copy number and target-site mutation variation at the canonical ace and ace-like genes and test for potential associations with organophosphate insensitivity. This was achieved through comparisons of whole-genome pool-seq data from alive and dead mites following organophosphate exposure. RESULTSA combination of increased copy number and target-site mutations at the canonical ace was associated with organophosphate insensitivity in H. destructor. Resistant populations were segregating for G119S, A201S, F331Y at the canonical ace. A subset of populations also had copy numbers of canonical ace >2, which potentially helps over-express proteins carrying these target-site mutations. Haplotypes possessing different copy numbers and target-site mutations of the canonical ace gene may be under selection across H. destructor populations. We also detected some evidence that increases in copy number of radiated ace-like genes are associated with organophosphate insensitivity, which might suggest potential roles in sequestration or breakdown of organophosphates. CONCLUSIONDifferent combinations of target-site mutations and (or) copy number variation in the canonical ace and ace-like genes may provide non-convergent ways for H. destructor to respond to organophosphate selection. However, these changes may only play a partial role in organophosphate insensitivity, which appears to have a polygenic architecture.

evolutionary biology↗

bioRxiv2022

Hidden endosymbionts: A male-killer concealed by another endosymbiont and a nuclear suppressor

Maternally transmitted endosymbiotic bacteria that cause male killing (MK) have only been described from a few insects, but this may reflect challenges in their detection rather than a rarity of MK. Here we identify MK Wolbachia in populations of Drosophila pseudotakahashii, present at a low frequency (around 4%) in natural populations and previously undetected due to a different fixed Wolbachia strain in this species expressing a different reproductive manipulation, cytoplasmic incompatibility (CI). The MK phenotype was eliminated after tetracycline treatment that removed Wolbachia. Molecular analyses indicated the MK phenotype to be expressed when a second Wolbachia strain was present alongside the CI Wolbachia. A genomic analysis highlighted Wolbachia regions diverged between the strains involving 17 genes and also identified the Wolbachia as representing an outgroup to a clade of Wolbachia infecting melanogaster-group species, including wRi-like and wMel-like strains. Doubly infected males induced CI with uninfected females but not females singly infected with CI-causing Wolbachia. The MK phenotype manifested at the larval stage and was transmitted maternally at a high fidelity but with occasional loss of the MK Wolbachia strain. A rapidly spreading dominant nuclear suppressor genetic element affecting MK was identified through backcrossing and subsequent analysis with ddRAD SNPs of the D. pseudotakahashii genome. These findings highlight the complexity of nuclear and microbial components affecting MK endosymbiont detection and dynamics in populations, and the challenges of making connections between endosymbionts and the host phenotypes affected by them.

evolutionary biology↗

bioRxiv2022

The redlegged earth mite draft genome provides new insights into pesticide resistance evolution and demography in its invasive Australian range

Genomic data provide valuable insights into pest management issues such as resistance evolution, historical patterns of pest invasions and ongoing population dynamics. We assembled the first reference genome for the redlegged earth mite, Halotydeus destructor (Tucker, 1925), to investigate adaptation to pesticide pressures and demography in its invasive Australian range using whole-genome pool-seq data from regionally distributed populations. Our reference genome comprises 132 autosomal contigs, with a total length of 48.90 Mb. We observed a large complex of ace genes, which has presumably evolved from a long history of organophosphate selection in H. destructor and may contribute toward organophosphate resistance through copy number variation, target-site mutations, and structural variants. In the putative ancestral H. destructor ace gene, we identified three target-site mutations (G119S, A201S, and F331Y) segregating in organophosphate resistant populations. Additionally, we identified two new para sodium channel gene mutations (L925I and F1020Y) that may contribute to pyrethroid resistance. Regional structuring observed in population genomic analyses indicates that gene flow in H. destructor does not homogenise populations across large geographic distances. However, our demographic analyses were equivocal on the magnitude of gene flow; the short invasion history of H. destructor makes it difficult to distinguish scenarios of complete isolation vs. ongoing migration. Nonetheless, we identified clear signatures of reduced genetic diversity and smaller inferred effective population sizes in eastern vs. western populations, which is consistent with the stepping-stone invasion pathway of this pest in Australia. These new insights will inform development of diagnostic genetic markers of resistance, further investigation into the multifaceted organophosphate resistance mechanism, and predictive modelling of resistance evolution and spread.

genomics↗

bioRxiv2022

Developing Wolbachia-based disease interventions for an extreme environment

Aedes aegypti mosquitoes carrying self-spreading, virus-blocking Wolbachia bacteria are being deployed to suppress dengue transmission. However, there are challenges in applying this technology in extreme environments. We introduced two Wolbachia strains into Ae. aegypti from Saudi Arabia for a release program in the hot coastal city of Jeddah. Wolbachia reduced infection and dissemination of dengue virus (DENV2) in Saudi Arabian mosquitoes and showed complete maternal transmission and cytoplasmic incompatibility. Wolbachia reduced mosquito heat tolerance and egg viability, with the Wolbachia strains showing differential thermal stability. Wolbachia effects were similar across mosquito genetic backgrounds but we found evidence of local adaptation, with Saudi Arabian mosquitoes having lower egg viability but higher adult desiccation tolerance than Australian mosquitoes. Genetic background effects will influence Wolbachia invasion dynamics, reinforcing the need to use local genotypes for mosquito release programs, particularly in extreme environments like Jeddah. Our comprehensive characterization of Wolbachia strains provides a foundation for Wolbachia-based disease interventions in harsh climates.

evolutionary biology↗

bioRxiv2022

Lipidomic change in Aedes aegypti female following blood feeding reveals similar changes in functionally related lipids

We conducted a lipidomic analysis of the whole body of female Aedes aegypti mosquitoes at different time points over the course of feeding and reproduction. There were temporal biphasic increases of more than 80% of lipids identified at the time of feeding and from 16 h to 30 h post blood meal. During these two increases, the abundance of many lipids dropped while body weight remained stable, probably reflecting blood lipid digestion and the synthesis of vitellogenin in this period. A concerted temporal pattern was particularly strong at the second peak for membrane and signalling lipids such as PE, PI, CL, HexCer and LPA. Lyso-glycerophospholipids showed three distinct change patterns which are functionally related: LPE and LPC, which are membrane lipids, showed little change; LPA, a signalling lipid, showed a dramatic increase from 16 to 30 h PBM; LPI, a bioactive lipid, and both LPG and LPS which are bacterial membrane lipids, showed one significant increase from the time of feeding to 16 hours post blood meal. The result of our study on the anautogenous insect Ae. aegypti point to specific lipids likely to be important in the reproductive process with a role in the formation and growth of ovarian follicles.

biochemistry↗

bioRxiv2022

Local adaptation of Aedes aegypti mosquitoes to Wolbachia-induced fitness costs

Aedes aegypti mosquito eggs can remain quiescent for many months before hatching, allowing populations to persist through unfavorable conditions. Aedes aegypti infected with the Wolbachia strain wMel have been released in tropical and subtropical regions for dengue control. wMel reduces the viability of quiescent eggs, but this physiological cost might be expected to evolve in natural mosquito populations that frequently experience stressful conditions. We therefore compared the costs of wMel infection for quiescent egg viability in field-derived and laboratory populations. Quiescent egg viability was highly variable in wMel-infected populations, with greater costs of wMel in field-derived populations. In contrast, there was little variation between matched field-derived and long-term laboratory populations lacking wMel, suggesting that laboratory adaptation does not influence this trait and that differences are due to wMel infection. Comparisons of populations collected a year apart show a decline in costs under laboratory rearing conditions involving a rapid turnover of mosquito generations; this pattern was consistent across populations despite their origin, suggesting adaptation of mosquitoes to the wMel infection under laboratory conditions. Reciprocal crossing experiments confirm that differences in quiescent egg viability were mainly due to the genetic background and not Wolbachia alone. wMel-infected mosquitoes hatching from long-term quiescent eggs showed partial loss of cytoplasmic incompatibility and female infertility, highlighting additional costs of long-term quiescence. Our study provides the first evidence for a shift in Wolbachia phenotypic effects following deliberate field release and establishment and it highlights interactions between Wolbachia infections and local adaptation. The unexpected changes in fitness costs observed here suggest potential tradeoffs with undescribed fitness benefits of the wMel infection.

evolutionary biology↗

bioRxiv2022

Incorporating selection pressures into risk predictions of chemical resistance evolution in pest organisms

Chemical resistance in pest organisms threatens global food security and human health, yet resistance issues are mostly dealt with reactively. Predictive models of resistance risk provide an avenue for field practitioners to implement proactive pest management but require knowledge of factors that drive resistance evolution. Despite the importance of chemical selection pressure on resistance evolution, poor availability of chemical usage data has limited the use of a general multi-species measure of selection pressure in predictive models. We demonstrate the use of pesticide product registrations as a predictor of resistance status and potential proxy of chemical selection pressure. Pesticide product registrations were obtained for 427 USA and 209 Australian agricultural arthropod pests, for 42 and 39 chemical Mode of Action (MoA) groups, respectively. We constructed Bayesian logistic regressions of resistance status as a function of the number of pesticide product registrations and two ecological traits, phagy and voltinism. Our models were well-supported with demonstrated power to discriminate between resistant and susceptible observations in both USA and Australian species sets using cross-validation. Importantly, we observed strong support for a positive association between pesticide products and resistance status. Our work expands the horizon for proactive management by quantitatively linking a proxy for selection pressure on pest species to different chemical MoAs. This proxy for selection pressure can be combined with ecological information to predict the resistance risk in agricultural pests. Because pesticide product registrations can typically be derived from publicly available data, we believe there is broad applicability to other agricultural pests such as weeds and fungi, and to other geographical regions beyond the USA and Australia.

evolutionary biology↗

bioRxiv2022

Wolbachia inhibits ovarian formation and increases blood avidity in female Aedes aegypti-a novel time-specific reproductive alteration

Wolbachia, a gram-negative endosymbiotic bacterium widespread in arthropods, is well-known for changing the reproduction of its host in ways that increase its rate of spread, but there are also costs to hosts that can reduce this. Here we investigated a novel reproductive alteration of Wolbachia wAlbB on its mosquito host Aedes aegypti, based on studies of mosquito life history traits, ovarian dissections and gene expression assays. We found that an extended period of the larval stage as well as the egg stage, as previously shown, can increase the proportion of Wolbachia-infected females that become infertile; the impact of Wolbachia on infertility therefore accumulated before pupation. We found that ovarian formation was blocked in infertile females, even though infected females had relatively lower Wolbachia densities than fertile infected females. Infertile females also showed a higher frequency of blood feeding following a prior blood meal, indicating that they do not enter a complete gonotrophic cycle. Treatments leading to infertility decreased expression of genes related to reproduction. Our results demonstrate effects related to the causes and consequences of infertile wAlbB-infected Ae. aegypti females with implications for Wolbachia releases and have evolutionary implications for Wolbachia infections in novel hosts.

microbiology↗

bioRxiv2022

Genomic and phenotypic comparisons reveal distinct variants of Wolbachia strain wAlbB

The intracellular bacterium Wolbachia inhibits virus replication and is being harnessed around the world to fight mosquito-borne diseases through releases of mosquitoes carrying the symbiont. Wolbachia strains vary in their ability to invade mosquito populations and suppress viruses in part due to differences in their density within the insect and associated fitness costs. Using whole-genome sequencing, we demonstrate the existence of two variants in wAlbB, a Wolbachia strain being released in natural populations of Aedes aegypti mosquitoes. The two variants display striking differences in genome architecture and gene content. Differences in the presence/absence of 49 genes between variants include genes located in prophage regions and others potentially involved in controlling the symbionts density. Importantly, we show that these genetic differences correlate with variation in wAlbB density and its tolerance to heat stress, suggesting that different wAlbB variants may be better suited for field deployment depending on local environmental conditions. Finally, we found that the wAlbB genome remained stable following its introduction in a Malaysian mosquito population. Our results highlight the need for further genomic and phenotypic characterization of Wolbachia strains in order to inform ongoing Wolbachia-based programmes and improve the selection of optimal strains in future field interventions. ImportanceDengue is a viral disease transmitted by Aedes mosquitoes that threatens around half of the world population. Recent advances in dengue control involve the introduction of Wolbachia bacterial symbionts with antiviral properties into mosquito populations which can lead to dramatic decreases in the incidence of the disease. In light of these promising results, there is a crucial need to better understand the factors affecting the success of such strategies, in particular the choice of Wolbachia strain for field releases and the potential for evolutionary changes. Here we characterized two variants of a Wolbachia strain used for dengue control that differ at the genomic level and in their ability to replicate within the mosquito. We also found no evidence for the evolution of the symbiont within the two years following its deployment in Malaysia. Our results have implications for current and future Wolbachia-based health interventions.

genomics↗