Whitefly disrupts plants' built-in alarm systems

When plants are bitten by insects, they release a chemical scream—a cocktail of compounds that travel through the air. Some deter pests directly by confusing or repelling them; others indirectly protect plants by summoning predatory ants or parasitic wasps. Still others raise the alarm in parts of the plant that aren’t yet under attack, telling them to ramp up their defenses in preparation. These same alarms can spread over entire fields, warning other plants to prep their defenses. We can’t perceive these signals, but to plants, they’re as foreboding as wailing sirens.

In very rough terms, plants have two main defense systems: one for insects and other plant-eating animals, and another for infectious microbes. The former centers on jasmonic acid, a hormone that triggers the production of insecticidal toxins. The latter centers on salicylic acid, a different hormone that triggers the production of antimicrobials, or tough molecules that barricade a plant’s cells against besieging microbes. In 2007, Sonia Zárate and Louisa Kempema from the University of California at Riverside showed that whiteflies induce the wrong defense—the antimicrobial salicylic-acid one, instead of the anti-insect jasmonic-acid one.

Now Peng-Jun Zhang and Xiao-Ping Yu from China Jiliang University have expanded on that finding by showing that these inappropriate defenses can cascade through an entire field. The team placed pairs of tomato plants in separate glass chambers, connected by tubes that allowed air to pass between them. If the first plant was infested with caterpillars, the second ramped up its anti-insect defenses. When caterpillars attacked that second plant, they had a tougher time and grew more slowly.

But if the first tomato was infested with whiteflies, everything went topsy-turvy. The plant released a very different airborne cocktail, which compelled its neighbor to turn down its anti-insect defenses and turn up the antimicrobial pathway. If whitefly larvae ended up on that misinformed tomato, they actually grew faster than they would have on plants that had received no warnings at all.

Read more at The Atlantic (Ed Yong)

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