The gut microbiome of the cabbage looper is modulated by tomato specialized metabolites

Plants protect their tissues from insect herbivory with specialized structures and chemicals, such as cuticles, trichomes and specialized metabolites. Bacteria inside the insect gut are also exposed to plant defences and could potentially modify the outcome of plant-insect interactions. To disentangle this complex multi-organism system, we used tomato mutants impaired in the production of specialized metabolites (odorless 2 and jasmonic acid insensitive1) and two cultivars (Ailsa Craig and Castlemart), exposed them to herbivory by the cabbage looper (Trichoplusia ni) and collected the insect frass for bacterial community analysis. From the plant perspective, epicuticular wax and terpene profiles showed significant differences. In contrast, the total leaf fatty acid composition did not differ among genotypes. From the insect side, larval weight was confirmed/supported the negative association between specialized metabolites and insect performance. Moreover, frass fatty acid profiles were found to be different from the consumed plant material. Lastly, the leaf and insect-gut bacterial communities were compared. The analysis showed that a small fraction of bacterial taxa was shared between leaf and frass samples. Moreover, insect bacterial community abundance and diversity substantially varied relative to plant host genotype. Altogether, these results indicate that plant defensive metabolites can modulate insect-associated bacterial community composition.