Biology subjects

Brevault, T.

Publications and source records attributed to Brevault, T..

6 recordsLinked to original sources

bioRxiv2026

Unraveling Environmental Drivers of Insect Pest Dynamics Across Multiple Landscapes

The persistence of pest populations during crop off-seasons is a major challenge for integrated pest management, yet the ecological processes underlying survival and re-infestation often remain unclear. We investigated the oriental fruit fly, Bactrocera dorsalis, a major mango pest, through a two-year demographic monitoring across 56 orchards in the two main mango production basins in Senegal: the Sahelian Niayes and the tropical Casamance. Using a framework combining mechanistic and machine learning models, we identified the main environmental drivers of two key demographic parameters: the local abundance during the mango off-season and the onset of population growth in orchards. In the Niayes, harsh dry-season conditions confined residual populations to micro-habitats providing humidity and shade, while alternative hosts such as citrus trees could act as catalysts for early outbreaks. In contrast, under tropical conditions in the Casamance basin, B.dorsalis populations were more abundant year-round, and higher off-season densities appear to delay outbreak onset, likely due to density-dependent processes such as competition and predation. These findings show that distinct ecological processes shape B. dorsalis off-season persistence across environments, thereby determining population carry-over and growth onset, and ultimately leading to contrasting population dynamics across environments. They support region-specific management strategies to effectively reduce pest pressure: targeting refuges and early host resources in the Niayes, and enhancing natural regulation in Casamance.

ecology↗

bioRxiv2025

Nested PCR to optimize rpoB metabarcoding for low-concentration and host-associated bacterial DNA

BackgroundHousekeeping genes have proved effective taxonomic markers for characterizing bacterial microbiota in short-read amplicon metabarcoding studies. A region of the rpoB gene, in particular, has been shown to minimize OTU overestimation bias with a high degree of accuracy, providing better species-level taxonomic resolution (Ogier et al. BMC Microbiol. 19:171). However, the primers for rpoB are highly degenerate, leading to potential problems in the amplification of bacterial DNA present at low concentration in the sample or embedded within eukaryotic matrices, as for the host-associated microbiota. We addressed these limitations by using a two-step PCR approach to optimize the rpoB procedure. The first PCR amplifies a 906-nucleotide region of the rpoB gene with the classical primers, referred to here as outer primers, and the second PCR then uses primers incorporating Illumina adapters, referred to here as inner primers, to amplify a 435-nucleotide subregion, the taxonomic marker for metabarcoding. ResultsWe first used in silico approaches to evaluate the universality of the outer and inner rpoB primers. We then tested the nested rpoB PCR method on commercial mock samples of known composition. The nested PCR approach increased amplification efficiency for dilute samples without biasing the bacterial composition of the mock sample revealed by metabarcoding relative to single-step PCR. We also tested the nested rpoB PCR method on field-collected samples of the lepidopteran Spodoptera frugiperda. The nested PCR outperformed single-step PCR, increasing amplification efficiency for bacterial DNA present at low concentrations (oral secretions from S. frugiperda) or embedded in eukaryotic DNA matrices (S. frugiperda larvae). ConclusionsThis method provides a promising new strategy for characterizing insect-associated microbiota that can also be applied to other host microbiomes.

microbiology↗

bioRxiv2024

Sex-specific sub-lethal effects of low virulence entomopathogenic fungi may boost the Sterile Insect Technique

BACKGROUNDThe Sterile Insect Technique (SIT) is a species-specific method for controlling insect pests. Recent studies have explored the combination of SIT with entomopathogenic microorganisms, known as boosted-SIT, to enhance its effectiveness. This study aimed to evaluate the potential of the entomopathogenic fungi, Metarhizium anisopliae, in boosting the SIT for managing the oriental fruit fly, Bactrocera dorsalis. METHODSAdult flies from a laboratory population of B. dorsalis were inoculated with one of eight strains of M. anisopliae to assess fungus virulence in each sex. Ideally, boosted-SIT should minimally impact sterile males and reduce female fecundity maximally. A brief exposure to fungal spores was efficient to infect males, and for them to transmit the fungus to females when hosted together for 24 hours. RESULTSOur results showed significant variations in the mortality induced by the strains in males, but not in females that exhibited low mortality. Strains varied in their sub-lethal effects on female fecundity, with almost a two-fold variation among strains. Furthermore, strains that had the lowest virulence on males tended to reduce female fecundity the most. CONCLUSIONOur study brings a proof of concept that it is possible to leverage boosted- SIT using carefully selected pathogen strains and their sub-lethal effects on both the male and female fruit fly.

ecology↗

bioRxiv2023

Inoculation dose, formulation and air temperature shape Metarhizium anisopliae virulence against the oriental fruit fly: lessons for improving on-target control strategies

Entomopathogenic fungi are a promising tool for the biological control of crop pests provided low or no impact on non-target organisms. Selection for host specificity as well as on-target applications open new avenues for more sustainable strategies for pest management. Isolates of Metarhizium anisopliae (Metschn.) Sorokin have been identified as promising for developing innovative entomovectoring-based strategies for the control of the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), in Africa. To be effective, this technology requires high strain virulence at a low number of spores, but sufficient incubation time to allow transmission to wild conspecifics. This depends on trophic interactions between the host and the pathogen, which are mediated by abiotic factors. In the present study, we investigated the virulence of the Met69 strain against adult flies, depending on the inoculation dose, air temperature and formulation. High pathogenicity was observed at very low inoculation doses (LT50 of 4.85 days with 6100 spores per fly) independently of fly sex. Virulence increased with spore load in a tight range (5600 and 6100 spores per fly) and with air temperature observed in the field (20-28{degrees}C). Unexpectedly, corn starch used as an adjuvant to increase the carrying capacity of insects decreased the virulence of the pathogen. The results will help improve area-wide control strategies based on the contamination of wild flies through auto-inoculation devices or interactions with released mass-reared sterile males coated with fungal spores. Furthermore, the study proposes an approach for calibrating area-wide control strategies, taking into account both the insect and pathogen bioecology and the environment in which they evolve. Author rolesAnais Chailleux: Conceptualization, Funding acquisition, Methodology, Data curation, Writing - original draft. Oumou Noumou Coulibaly: Investigation, Writing - original draft. Babacar Diouf: Investigation, Visualization. Samba Diop: Investigation. Ahmad Sohel: Resources, Writing - review & editing. Thierry Brevault: Conceptualization, Funding acquisition, Project administration, Writing - review & editing.

zoology↗

bioRxiv2023

Hierarchizing multi-scale environmental effects on agricultural pest population dynamics: a case study on the annual onset of Bactrocera dorsalis population growth in Senegalese orchards

Implementing integrated pest management programs to limit agricultural pest damage requires an understanding of the interactions between the environmental variability and population demographic processes. However, identifying key environmental drivers of spatio-temporal pest population dynamics remains challenging as numerous candidate factors can operate at a range of scales, from the field (e.g. agricultural practices) to the regional scale (e.g. weather variability). In such a context, data-driven approaches applied to pre-existing data may allow identifying patterns, correlations, and trends that may not be apparent through more restricted hypothesis-driven studies. The resulting insights can lead to the generation of novel hypotheses and inform future experimental work focusing on a limited and relevant set of environmental predictors. In this study, we developed an ecoinformatics approach to unravel the multi-scale environmental conditions that lead to the early re-infestation of mango orchards by a major pest in Senegal, the oriental fruit fly Bactrocera dorsalis (BD). We gathered abundance data from a three-year monitoring conducted in 69 mango orchards as well as environmental data (i.e. orchard management, landscape structure and weather variability) across a range of spatial scales. We then developed a flexible analysis pipeline centred on a recent machine learning algorithm, which allows the combination of gradient boosting and grouped random effects models or Gaussian processes, to hierarchize the effects of multi-scale environmental variables on the onset of annual BD population growth in orchards. We found that physical factors (humidity, temperature), and to some extent landscape variables, were the main drivers of the spatio-temporal variability of the onset of population growth in orchards. These results suggest that favourable microclimate conditions could provide refuges for small BD populations that could survive, with little or no reproduction, during the mango off-season and, then, recolonize neighbouring orchards at the beginning of the next mango season. Confirmation of such a hypothesis could help to prioritize surveillance and preventive control actions in refuge areas.

ecology↗

bioRxiv2020

Genomic balancing selection is key to the invasive success of the fall armyworm

A successful biological invasion involves survival in a newly occupied environment. If a population bottleneck occurs during an invasion, the resulting depletion of genetic variants could cause increased inbreeding depression and decreased adaptive potential, which may result in a fitness reduction. How invasive populations survive in the newly occupied environment despite reduced heterozygosity and how, in many cases, they maintain moderate levels of heterozygosity are still contentious issues1. The Fall armyworm (FAW; Lepidoptera: Spodoptera frugiperda), a polyphagous pest, is native to the Western hemisphere. Its invasion in the Old World was first reported from West Africa in early 2016, and in less than four years, it swept sub-Saharan Africa and Asia, finally reaching Australia. We used population genomics approaches to investigate the factors that may explain the invasive success of the FAW. Here we show that genomic balancing selection played a key role in invasive success by restoring heterozygosity before the global invasion. We observe a drastic loss of mitochondrial polymorphism in invasive populations, whereas nuclear heterozygosity exhibits a mild reduction. The population from Benin in West Africa has the lowest length of linkage disequilibrium amongst all invasive and native populations despite its reduced population size. This result indicates that balancing selection increased heterozygosity by facilitating the admixture of invasive populations from distinct origins and that, once heterozygosity was sufficiently high, FAW started spreading globally in the Old World. As comparable heterozygosity levels between invasive and native populations are commonly observed1, we postulate that the restoration of heterozygosity through balancing selection could be widespread among successful cases of biological invasions.

evolutionary biology↗