Sticky trick: new glue spray kills plant pests without chemicals

<span>Chemical pesticide use has risen by 50% in the past three decades, but researchers believe they have found a green alternative.</span><span>Photograph: Loop Images/Universal Images Group/Getty Images</span>
Chemical pesticide use has risen by 50% in the past three decades, but researchers believe they have found a green alternative.Photograph: Loop Images/Universal Images Group/Getty Images

Tiny sticky droplets sprayed on crops to trap pests could be a green alternative to chemical pesticides, research has shown.

The insect glue, produced from edible oils, was inspired by plants such as sundews that use the strategy to capture their prey. A key advantage of physical pesticides over toxic pesticides is that pests are highly unlikely to evolve resistance, as this would require them to develop much larger and stronger bodies, while bigger beneficial insects, like bees, are not trapped by the drops.

Pests destroy large amounts of food and chemical pesticide use has risen by 50% in the past three decades, as the growing global population demands more food. But increasing evidence of great harm to nature and wildlife, and sometimes humans, has led to a rising number of pesticides being banned.

Some farmers already use alternatives to chemical pesticides, such as introducing other insects that kill the pests, but the new sticky drops are thought to be the first such biodegradable pesticide to be demonstrated.

The drops were tested on the western flower thrip, which are known to attack more than 500 species of vegetable, fruit and ornamental crops. More than 60% of the thrips were captured within the two days of the test, and the drops remained sticky for weeks.

Work on the sticky pesticide is continuing, but Dr Thomas Kodger at Wageningen University & Research, in the Netherlands, who is part of the self defence project doing the work, said: “We hope it will have not nearly as disastrous side-effects on the local environment or on accidental poisonings of humans. And the alternatives are much worse, which are potential starvation due to crop loss or the overuse of chemical pesticides, which are a known hazard.”

The research, published in the journal Proceedings of the National Academy of Sciences, took an edible plant oil and oxidised it to make it as sticky as duct tape, a process similar to deep frying. The oil was then blitzed in a “glorified blender” along with water and a little soap to stop the droplets sticking together.

This solution was then sprayed on to the leaves of chrysanthemum plants, the thrips’ favourite food and a huge commercial crop in the Netherlands. It was also tested on strawberries. The sprayers used are the same design as those already used by farmers and field trials this summer will test the process at scale.

Fly paper already exists but obviously cannot be sprayed and Kodger said: “Fly traps are extremely effective against pests but they’re also extremely effective against pollinators.” He said bees were too big and strong to get stuck in the millimetre-size drops.

The team is testing to see if scents can be incorporated into the droplets to make them even more attractive to the thrips or to attract natural predators of the pests such as Orius laevigatus, a pirate bug that is already sold as a control measure for thrips.

The sticky drops will biodegrade but the team is investigating how long this takes. It is also assessing how quickly dust reduces the stickiness of the drops, though this is expected to be less of an issue in greenhouses where many horticultural crops are grown.

The cost of the sticky drop pesticide is uncertain as it is not yet known how much will need to be applied and how often, though the raw material could be cheap waste oil. The team is applying for a patent founding a spin-off company to commercialise the product.

Nick Mole, from Pesticide Action Network UK, said: “This is a very interesting piece of research that could result in much-needed decreases in the use of synthetic pesticides. Using natural oils to make physical traps for disease-carrying insects could be a sustainable alternative to toxic pesticides. More research is required to assess the impact on the environment and non-target insect species, but it definitely looks promising.”

“Innovative approaches to replacing toxic pesticides are welcome,” said Craig Macadam, at the invertebrate charity Buglife. “For too long our countryside has been poisoned by toxic chemicals contributing to a significant loss of pollinators and aquatic invertebrates. However, any replacement must undergo a rigorous assessment process to ensure all non-target species are properly protected.”

Kodger said: “Growers feel like all of these [chemical pesticides] are being taken away by regulators. We want to give them a new fighting tool that is not harmful for the environment. It is rewarding to witness our idea potentially changing the world within my lifetime.”