Biopesticides, such as spinosad, are a new generation of pesticides that are showing promise in the livestock industry by posing a triple threat. Their production has less effect on the environment, they’re made from natural products, and they have been demonstrated to be highly effective at dealing with cattle pests such as ticks in laboratory settings.
Unaided however, spinosads quickly degrade in sunlight and can be easily washed away by rainfall – this means that they become largely ineffective within in a week in the field, making them prohibitively expensive and impractical as they would have to be reapplied every few days.
Inspiration was needed and it came to Jun Zhang and a team at The University of Queensland who looked at naturally occurring particles like pollen, bacteria, and viruses that use a spikey outer shell to latch on to animal hides. The team produced their own prickly nanoparticles, and loaded them with pesticides.
Nanoparticles can be fabricated in a number of ways, depending on the properties required and the materials used. They can be created by simply spraying tiny droplets of molten material into a cooling bath, much like miniature musket bullets; or by coating a seed particle with material, similar to how pearls form.
In this instance, a resin core is used as a base to grow a layer of silica on the surface. When the resin is removed, a hollow shell remains. The resin was also instrumental in allowing the spikes to form on the outer edge of the shell, providing support as the delicate spines grew.
Once these nanoparticles are produced, they are mixed in with the spinosad solution in a vacuum which allows solvent to be evaporated away at temperatures that won’t damage either the pesticide or the particles. By reducing the mixture in this way, the nanoparticles adsorb the pesticide leaving them loaded and ready for application.
The team then had to see how their new nanospinosad particles performed. To understand the adhesive qualities, they worked with ANFF experts at UQ to perform fluorescent confocal microscopy. Their nanospinosad was labelled with a green fluorescent probe, which was then used to keep track of the distribution of the particles latched on to ticks. “In the field” testing was then simulated by coating a cattle hide with nanospinosad and exposing it to conditions such as wind, sun and rain in the lab and in open air.
The research demonstrated that their work had paid off, with the particles both protecting the biopesticide from sunlight and improving its ability to latch on to cattle hides and pests. In fact, due to its improved adhesive capabilities, the team’s nanospinosad outperformed benchmark commercial spinosads by killing more ticks, and also showed a 10-fold increase in photostability compared to the off-the-shelf products in simulated field conditions. The result is an effective, ecofriendly pesticide that doesn’t need to be reapplied on a weekly basis, saving time, energy, money and the environment in a single shot.