Mediation of induced plant defenses by the gut symbionts of insects herbivores

We contend that the study of plant-herbivore interactions needs to be considered in the context of the microbiomes of both the plant and the herbivore. Using an experimental system comprised of caterpillar and beetle herbivores, we have shown that gut bacteria play an important role in mounting induced plant defences. Gut bacteria and their microbe associated molecular patterns (MAMPs) may be directly applied to the plant during herbivore feeding and regurgitation. Plants may then perceive the MAMPs and upregulate the salicylic acid pathway, with a concomitant suppression of jasmonate signalling. This negative cross-talk may be relatively common among chewing herbivores such as beetles that freely regurgitate during feeding. Alternatively, we have shown that the gut bacteria in some herbivores may indirectly regulate the expression or synthesis of herbivore effectors and elicitors thus affecting plant signalling. This latter finding has likely been overlooked because many studies with herbivores such as caterpillars have been conducted with lab colonies of insects, which have lost a significant segment of their bacterial community during rearing in the lab. The ability to disrupt the insectÕs natural microbiota (=dysbiosis) offers a viable novel strategy for pest protection.