By riffing off of insect biology, researchers have found an alternative to the indiscriminate spraying of insecticides across farms: they’ve developed a material that gradually releases insect pheromones, attractive chemicals that can entice specific species to traps spread across a field—throwing them off course from the crop itself.
The material, described in a study led by researchers from the University of Bath in the UK, was developed specifically with leaf-cutter ants in mind. These ants cause billions of dollars worth of damage on farms in neotropical countries like Brazil every year, by efficiently dismantling and carrying away vast amounts of new growth in their jaws. It’s difficult to control these insects with pesticides, because these chemicals are prone to degrading in the warm, wet, regional conditions. And what’s more, they have dire effects on multiple other non-target species, and they contaminate the surrounding environment—two common caveats of all pesticides.
As an alternative to this, the researchers on the new study explored how they might instead take a more targeted approach to pest control. They set their sights on metal-organic frameworks (MOFs) – a type of material that’s made up of compounds organized into a structure that creates nano-scale pores within, which can store chemicals. This sponge-like framework also makes it possible for stored chemicals to be diffused into the surroundings. MOF materials devices are already being tested for use in many applications—including in medical settings to provide controlled-release drug delivery to patients.
The researchers were curious to find out whether MOFs could do the same with insect pheromones, instead—specifically, powerful pheromones that leaf-cutter ants use to communicate alarm signals to one another, when there’s a threat to the colony. Conveniently for the researchers’ purposes, these particular pheromones work by attracting ants rapidly to the site of release, where they then rally to dispatch the threat.
Because these compounds also happen to be highly volatile, the researchers used a computational model to simulate how the structure of the MOF would affect the rate of release of these pheromones from the material. Ideally, they wanted to develop a structure that would ensure a steady, gradual release, so that the device would be effective over long periods of time in the field.
Using this model, they homed in on a structural design that would release pheromone compounds in incremental doses, for months at a time. “With all of the MOFs we looked at, we found quite a wide range of release profiles, but our best example was still releasing the pheromone after 100 days,” says Andrew Burrows, lead author on the study and professor of inorganic chemistry at the University of Bath.
With the mechanism firmly established, the researchers then took their model out into the field. In anon-farm trials in Brazil, they were able to show that the pheromone-soaked MOF was indeed able to attract the target leaf-cutter ants. This demonstrated that the pheromone concentration was powerful enough to trigger normal responses in the insects, tricking them into thinking there was a threat they had to eradicate.
If MOF structures are spread evenly across a field, the researchers surmise, they could be used to attract ants to specific locations where they could then be trapped—intercepting their path onwards to crops. This set-up would probably have the best effects on small fields with high-value crops, the researchers note.
Because groups of pheromones and other signaling chemicals are specific to different species, this slow-releasing MOF tool could be used to target many other types of insect pests—but most importantly, while protecting other organisms that are present on agricultural fields. In fact, they’re now working on developing MOFs containing slow-release chemical messengers that target moth species which attack fruit orchards in the UK.
Insect-luring traps have been used before on farms, but this refined material will be more effective, the researchers hope. “I think the major advance we can bring is twofold—increasing the lifetime of the devices and, in the longer term, moving towards more environment-triggered release,” Burrows says. “I think if we can realise these goals in practice, we should be able to better target pesticide use, which will have environmental and economic benefits.”
As Burrows and his colleagues note in their study, the need for more food, and therefore pest control, isn’t going away. This more targeted approach could be a starting point that’s at least more sustainable than the legacy of conventional pesticides that farming has left in its wake.
Source: Burrows, et. al. “Inclusion and release of ant alarm pheromones from metal–organic frameworks.” Dalton Transactions. 2020.
Image: Wikimedia Commons
