Some caterpillars use bacteria to alter leaves

The larvae of some leaf-eating insects live not on the surface of the leaf, but inside it; these are the leaf-miners, whose munching paths can be quite prominent.  Since the leaf is home as well as food, it is useful to the critter to help the leaf stay alive.  It's now been discovered that some larvae use commensal bacteria to enhance the health of at least part of the leaf, creating green islands within a dying leaf.

The bacteria were the true agents behind the green islands. When Kaiser cured the leaf-miners of their infections using antibiotics, they seemed perfectly healthy. But they completely lost the ability to stem the yellowing of leaves. As a result, 85% perished before adulthood; for comparion, the typical mortality rate of Wolbachia-carrying larvae is just 10%. Worst of all, since Wolbachia is passed down from mother to offspring, later generations also suffered the same lack of beneficial bacteria, the same inability to produce green islands and the same high odds of an early death.

The bacteria manipulate the leaves using their own signalling chemicals – a group of plant hormones called cytokinins. These substances perform many tasks in a leaf: they maintain the supply of chlorophyll; they prevent the leaf from dying; and they control the flow and storage of nutrients. They’re the barrier that stands between a living leaf and a rotting one. Stick cut plants in cytokinin solution and they’ll stay green for longer. What better tool for a bacterium or an insect looking to prolong the life of its leafy home?

More details at the Not Exactly Rocket Science link.  Amazing.  You learn something every day.   I'm going to look for these kinds of leaves this autumn.