Context
The fall armyworm (Spodoptera frugiperda) is a highly polyphagous Lepidoptera native to the
Americas, now widely established in Africa where it poses a major threat to crops, especially
maize. Since its arrival in 2016, it has rapidly spread across the continent, causing major
agricultural and economic damage (Goergen et al., 2016). Control strategies rely heavily on
insecticides, in particular pyrethroids such as λ-cyhalothrin and avermectins such as
emamectin benzoate (Ndung’U et al., 2023). However, S. frugiperda populations already show
resistance to a wide range of insecticides (up to 21 molecules across 10 chemical classes;
Ngegba et al., 2025). Resistance may be mediated by genetic mutations, enhanced
detoxification pathways, behavioral changes, or interactions with microbial symbionts
(Boaventura et al., 2020; Li et al., 2007). The role of the insect gut microbiome in resistance
phenomena is gaining increasing attention. In S. frugiperda, bacteria from the genera
Enterococcus and Pseudomonas are regularly identified as core members of the gut
microbiome, regardless of host strain or geographical origin (Oliveira et al., 2023). De Almeida
et al. (2017) demonstrated in vitro the ability of Pseudomonas to degrade insecticides,
suggesting a possible role in resistance. Similarly, Enterococcus species have been identified
as active members of the microbiome, capable of modulating the microbial community and
contributing to the host’s immune defense.
Objectives of the internship
This project aims to explore the link between gut microbiome composition and λ-cyhalothrin
resistance in S. frugiperda larvae, using a laboratory-susceptible strain together with a
collection of field-isolated bacteria. The goal is to assess whether specific gut bacteria
contribute to resistance against λ-cyhalothrin. To test this hypothesis, different experimental
lines will be compared: a dysbiotic line (with a strongly depleted microbiome), a line
recolonized with a bacterial cocktail derived from the field, lines recolonized with specific
bacterial isolates, and a non-modified control line.
The project will combine:
Microbiome manipulations (axenization, bacterial recolonization).
Insecticide bioassays with λ-cyhalothrin to determine survival and lethal doses
(LD50).
Molecular analyses (RNA extraction and RT-qPCR) to measure expression of
detoxification genes such as cytochrome P450s.
This project will give the student experience with both experimental entomology,
microbiology and molecular biology.
Internship environment
The internship will be supervised by Julie Sénécal (PhD student, CBGP, DGIMI), with co-
supervision from Marion Javal (IRD, CBGP) and Enric Frago (CIRAD, CBGP), in collaboration
with Sophie Gaudriault (UMR DGIMI).
The work will take place in Montpellier (France), at both CBGP and DGIMI facilities.
Candidate profile
We are looking for a motivated Master’s student with an interest in experimental biology,
microbiology, entomology, and molecular ecology. The candidate should be comfortable
handling and manipulating insects. Skills in laboratory experimentation and data analysis (R)
will be an advantage.
Practical information
Duration: 6 months (January-June 2026)
Location: Montpellier, France, CBGP, DGIMI
How to apply
Interested candidates should send their application (CV, motivation letter) by October 15, 2025, to :
Julie.senecal@ird.fr & Marion.javal@ird.fr
Reference
Goergen, G., Kumar, P. L., Sankung, S. B., Togola, A., & Tamò, M. (2016). First report of outbreaks of
the fall armyworm Spodoptera frugiperda (J. E. Smith) (Lepidoptera, Noctuidae), a new alien invasive
pest in West and Central Africa. PLOS ONE, 11(10), e0165632.
https://doi.org/10.1371/journal.pone.0165632
Ndung’u, K. E., Khamis, F. M., Ajene, I. J., Mbogo, K. O., & Akutse, K. S. (2023). Spodoptera
frugiperda population structure and influence of farmers’ practices on gut biodiversity for sustainable
management of the pest in Kenya. Frontiers in Ecology and Evolution, 11, 1235558.
https://doi.org/10.3389/fevo.2023.1235558
Ngegba, P. M., Khalid, M. Z., Jiang, W., & Zhong, G. (2025). An overview of insecticide resistance
mechanisms, challenges, and management strategies in Spodoptera frugiperda. Crop Protection,
107322. https://doi.org/10.1016/j.cropro.2025.107322
Boaventura, D., Martin, M., Pozzebon, A., Mota-Sanchez, D., & Nauen, R. (2020). Monitoring of
target-site mutations conferring insecticide resistance in Spodoptera frugiperda. Insects, 11(8), 545.
https://doi.org/10.3390/insects11080545
Li, X., Schuler, M. A., & Berenbaum, M. R. (2007). Molecular mechanisms of metabolic resistance to
synthetic and natural xenobiotics. Annual Review of Entomology, 52, 231–253.
https://doi.org/10.1146/annurev.ento.52.110405.091407
De Oliveira, N. C., & Cônsoli, F. L. (2023). Dysbiosis of the larval gut microbiota of Spodoptera
frugiperda strains feeding on different host plants. Symbiosis, 89(2), 197–211.
https://doi.org/10.1007/s13199-023-00907-x
e Almeida, L. G., et al. (2017). The gut microbiota of insecticide-resistant insects houses insecticide-
degrading bacteria: A potential source for biotechnological exploitation. PLOS ONE, 12(3), e0174754.
https://doi.org/10.1371/journal.pone.0174754
Wu, Y., Zheng, Y., Chen, Y., Wang, S., Chen, Y., Hu, F., & Zheng, H. (2020). Honey bee (Apis
mellifera) gut microbiota promotes host endogenous detoxification capability via regulation of P450
gene expression in the digestive tract. mBio, 11(2), e00377-20. https://doi.org/10.1128/mBio.00377-20
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