Silicon powers more than electronics: In tomato plants, it fuels a complex defense system that could help farmers use fewer pesticides.

Tomato plants on four continents are currently under attack from the South American tomato pinworm (Tuta absoluta), which destroys billions of dollars of crops each year. The impact can be particularly devastating for small-scale farmers in Africa, where the pest has invaded over the last decade, says chemical ecologist Baldwyn Torto of the International Centre of Insect Physiology and Ecology in Nairobi, Kenya. These pinworms, also known as tomato leaf miners, have become resistant to heavily used chemical pesticides, says ICIPE molecular biologist Fathiya Khamis — so new solutions are urgently needed.

Researchers knew that adding silicon to soil can fortify some crops against pests. Some plants use the element to physically strengthen their cells; tomatoes use silicon to kick-start a complex array of biochemical and genetic defense systems. Now, Torto, Khamis and their colleagues have uncovered some specifics of how silicon transforms tomatoes into pinworm-killing machines, the team reports in the March 24 Proceedings of the National Academy of Sciences.

When the researchers supplemented tomato plants’ soil with silicon-containing nanoparticles and exposed the plants to pinworm moths, the tomato stems produced a mysterious dark goo at the base of hairlike structures called trichomes. This dark substance appeared to lure pinworm mothers into laying eggs more frequently on tomato stems, instead of mostly on leaves. When pinworm caterpillars hatched and ate this “larval toffee,” they often did not survive.

The researchers analyzed the gooey substance and found a blend of sugars and wax. This mix was enticingly sweet but contained the wrong blend of nutrients to support caterpillar growth. To make matters worse for the pinworms, this plant potion also altered caterpillar microbiomes. Droppings from pinworms that ate the substance released a blend of gases that attracted two different species of pinworm-killing insects.

More information about how and where these tomatoes accumulate silicon is needed to confirm silicon’s role in this response, says plant pathologist Lawrence Datnoff of Louisiana State University in Baton Rouge. Datnoff, who was not involved with the study, points out that different tomato plants accumulate silicon in different ways, so “you’ve got to have the right controls.” Despite this, Datnoff says he has long advocated for using silicon to manage plant health. 

The researchers say that this study is the first step toward testing various silicon formulations for optimal crop yield and pest resistance, which could ultimately apply to other similar insects as well as the tomato pinworm. “This is good for the farmer,” Torto says. “You are basically enhancing biological control of the pests.”