Photostability assessment of natural pyrethrins using halloysite nanotube carrier system

Natural pyrethrins are one of the most used pesticides and insect repellent employed for domestic or agronomic use. However, they are highly hydrophobic and suffer of insolubility in water media and ready decomposition by photochemical, and oxidative actions. These aspects hamper their long-term storage and applicability. Herein, we report the synthesis and characterization of a nanomaterial based on the loading of pyrethrum extract (PE) into natural, low-cost and eco-compatible halloysite nanotubes (Hal). The Hal/PE nanomaterial was thoroughly characterized, and the morphology was imaged by TEM and SEM investigations. Release experiments showed a slow release of pyrethrins from the carrier, and photodegradation studies, both in solution and in solid state, highlighted that the pyrethrum extract in the Hal/PE nanomaterial showed high stability to UV irradiation, as proved by UPLC-ESI-MS, UV-vis and circular dichroism measurements. Furthermore, to check if the obtained nanomaterial possesses the insecticidal activity of the pyrethrum, in vivo tests on two model insects, Galleria. mellonella and Tenebrio molitor, were performed. The pyrethrins loaded onto Hal showed the same activity as standard pyrethrins, at half dose compared to them.