Insects use plants to deliver chemical messages to future insects

June 30, 2012
InsectCage_voicemail

Study setup: insect cage (credit: NIOO-KNAW)

A new study shows that herbivorous (plant-eating) insects can leave chemical messages to other insects in the soil that plants can pass on to other insects.

Researchers from the Netherlands Institute of Ecology (NIOO-KNAW) and Wageningen University (WUR) discovered this unique messaging service, which uses the composition of fungi in the soil, in the ragwort plant.

A few years ago, NIOO scientists discovered that soil-dwelling and aboveground insects are able to communicate with each other using the plant as a medium. Insects eating plant roots change the chemical composition of the leaves, causing the plant to release volatile signals into the air. This can convince aboveground insects to select another food plant in order to avoid competition and to escape from poisonous defence compounds in the plant.

The new research now shows that insects can also leave a specific legacy message that remains in the soil after they have fed on a plant. And future plants growing on that same spot can pick up these signals from the soil and pass them on to other insects. The new plant can also tell whether the former one was suffering from leaf-eating caterpillars or from root-eating insects.

“The new plants are actually decoding a ‘voicemail’ message from the past sent to the next generation of plant-feeding insects, and their enemies,” says NIOO researcher and first author Olga Kostenko. This message from the past then strongly influences the growth and possibly also the behavior of these future bugs.

Kostenko and her colleagues grew ragwort plants in a greenhouse and exposed them to leaf-eating caterpillars or root-feeding beetle larvae. Then they grew new plants in the same soil and exposed them to insects again. “What we discovered is that the composition of fungi in the soil changed greatly and depended on whether the insect had been feeding on roots or leaves,” explains Kostenko. “These changes in fungal community, in turn, affected the growth and chemistry of the next batch of plants and therefore the insects on those plants.”

Growth and palatability of new plants in the same soil thus mirrored the condition of the previous plant. In this way, a new plant can pass down the soil legacy or message from the past to caterpillars and their enemies.