Endophytic colonization of Bacillus thuringiensis on tomato reduces Spodoptera littoralis survival

Beneficial microorganisms can promote positive effects on plant biology, plant growth and defence barriers, offering a valuable alternative to synthetic agrochemicals. Bacillus thuringiensis (Bt) is an entomophatogen successfully applied as bioinsecticide worldwide and its ability to naturally colonize plants has been recently demonstrated. While the role of Bt as entomophatogen is well studied, its role as plant endophyte is still relatively less explored. Here we contribute to this research topic by studying the effect of tomato plants colonization by Bt on the survival and the development of the phytophagous pest Spodoptera littoralis (Lepidoptera: Noctuidae). Endophytic Bt negatively affected the survival of the first two larval instars that fed on detached leaves of colonized plants. The larvae which were able to reach the third instar developed normally and pupated, but exhibited higher pupal mortality, and the emerging adults exhibited lower fertility and longevity. In addition, S. littoralis larvae feeding on Bt-colonized plants were more susceptible to sublethal doses of Xentari, a commercial bioinsecticide containing the entomophatogen Bt. Further studies are underway to better characterize the mechanism underlying this thritrophic interaction between microorganism, plant and insect. Our results show a clear effect of Bt-colonized plants on S. littoralis larvae, which could contribute to a reduction in pesticide use in agriculture by directly suppressing this pest or enhancing its susceptibility to biocontrol agents.