Insecticide has its uses in controlling harmful pests that could otherwise devastate crops. The trouble, of course, is that oftentimes the use of insecticides comes at grave environmental costs.

By spraying harmful insecticides liberally on their crops, farmers can decimate species, including key pollinators like bees, and devastate fragile ecosystems. Worse: wind and rainwater often carry dangerous chemicals far and wide beyond farms, making their effects felt at a long distance.

A team of chemists and chemical engineers at Universities of Bath and Sussex has devised an ingenious way to limit the use of insecticides: by insects to traps laced with the chemicals. Rather than spray entire crops with pesticides, farmers can place traps laced with insecticides in certain areas for more targeted protection.

The scientists have done this by making use of the pheromones of leafcutter ants to attract these harmful pests to insecticide-laced baits. The ants, which can devastate plants, release chemicals that send signals to other ants about which way to go. Harnessing the power of these pheromones for pest control is a nifty trick.

“Leaf-cutting ants are major pest species of agriculture and forestry in many areas of the tropics causing an estimated $8 billion damage each year to eucalyptus forestry in Brazil alone,” the scientists explain. “Traditional pesticides often degrade quickly and are not specific to particular pests, resulting in substantial wastage of pest control products, environmental contamination and harmful effects on other insects.”

The scientists have created molecular sponges called metal-organic frameworks to soak up the alarm pheromones of leafcutter ants before releasing them slowly to attract the insects to a trap. They also altered certain chemicals so that they could adjust the speed at which pheromones are released to make them last for several months and not just days.

“Insect pheromones have been used previously for attracting pests, but the trouble is they are quite volatile, so their effects don’t last very long,” explains Prof. Andrew Burrows, head of the Department of Chemistry at the University of Bath. “Our metal-organic frameworks act as a kind of sponge where the pheromones can be encapsulated in the pores and then released slowly over time.”

The researchers’ field trials at a eucalyptus plantation in Brazil worked well, indicating that the pheromone-loaded MOFs can attract the ants to a trap.

“This system could reduce the amount of pesticides sprayed on a crop and could be particularly useful for high value crops in small areas,” Burrows says. “We’re currently looking at a range of other insect messenger chemicals including those that can be used to control moth pest species in UK fruit orchards.”

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