Sticky oil sprayed onto plants offers alternative to pesticides

Sticky traps consisting of tiny oil droplets can be sprayed onto plants to catch small pests while leaving larger insects such as bees unharmed. The researchers who developed the product hope it will help reduce the use of chemical pesticides.

The inspiration came from insect-trapping hairs with sticky tips, called glandular trichomes, found on some plants, says Thomas Kodger at Wageningen University in the Netherlands. Sundews, which capture insects as a source of nutrients, are probably the best-known example of plants with glandular trichomes, but many others have them for defence against herbivorous pests.

The difficult part of the oil idea was finding a formulation that would work with the sprayers already used by growers, rather than requiring specialised equipment, says Kodger. The team’s solution is to oxidise certain vegetable oils and mix them vigorously with water to create tiny droplets mostly less than a millimetre in diameter.

The resulting particles don’t clog up sprayers but do stick to plants for weeks. “It’s literally oil, air, a little bit of heat and patience,” says Kodger.

The spray-on traps work in the same way as the sticky papers and glue traps long used to catch other pests, by physically trapping tiny animals. The advantages of the spray-on traps is that they are on the plants themselves and don’t catch bigger insects, including beneficial ones such as bees and hoverflies.

“One of the reasons larger [sticky] traps are not used in greenhouses today is because they devastate pollinators and other beneficial insects,” says Kodger.

In their tests, the researchers found that after the sticky traps were sprayed on plants, they caught at least five or six out of every 10 adult thrips that were put on the plants, he says. Thrips are a group of tiny sap-sucking insects that can seriously damage many plants, from chrysanthemums to tomatoes.

The spray-on approach is even more effective when it comes to trapping thrip larvae, says Kodger. “We have recent data that shows it prevents population explosions.”

For crops such as tomatoes, the idea would be to spray plants before fruits develop, but the spray is non-toxic, he says, and certainly safer than chemical pesticides. The team plans to apply for regulatory approval in Europe within a year.

The researchers are also exploring adding insect attractants produced by plants, either to attract the pests or to attract predators of pests, to allow the traps to be tailored to target different kinds of small plant pests. Tailoring could also be done by changing the size of the particles.