Résumé
Many studies have revealed the ability of the endosymbiotic
bacterium Wolbachia to protect its arthropod hosts
against diverse pathogens. However, as Wolbachia may
also increase the susceptibility of its host to infection, predicting the
outcome of a particular Wolbachia-host-pathogen interaction
remains elusive. Yet, understanding such interactions and their
eco-evolutionary consequences is crucial for disease and pest control
strategies. Moreover, how natural Wolbachia infections
affectartificially introduced pathogens for biocontrol has never been
studied. Tetranychus urticae spider mites are
herbivorous crop pests, causing severe damage on numerous economically
important crops. Due to the rapid evolution of pesticide
resistance, biological control strategies using entomopathogenic
fungi are being developed. However, although spider mites are
infected with various Wolbachia strains worldwide,
whether this endosymbiont protects them from fungi is as yet unknown.
Here, we compared the survival of two populations, treated with
antibiotics or naturally harbouring
different Wolbachia strains, after exposure to the
fungal biocontrol agents Metarhizium
brunneum and Beauveria bassiana. To control for
potential effects of the bacterial community of spider mites, we also
compared the susceptibility of two populations naturally uninfected
by Wolbachia, treated with antibiotics or not. In one
population, Wolbachia-infected mites had a better survival than
uninfected ones in absence of fungi but not in their presence,
whereas in the other population Wolbachia increased the
mortality induced by B. bassiana. In one
naturally Wolbachia-uninfected populations, the antibiotic
treatment increased the susceptibility of spider mites to M.
brunneum, but it had no effect in the other treatments. These
results suggest that natural Wolbachia infections may
not hamper and may even improve the success of biological control using
entomopathogenic fungi. However, they also draw caution on the
generalization of such effects, given the complexity of
within-host pathogens interaction and the
potential eco-evolutionary consequences of the use
of biocontrol agents for Wolbachia-host associations.