Characterization of β-cyclodextrin - fennel and basil essential oil inclusion complexes and effect on Colorado potato beetle growth

Abstract

Essential oils (EOs) obtained from plants can frequently exhibit toxicity and repellency/deterrence against insect pests. Fennel (Foeniculum vulgare Mill.) and basil (Ocimum basilicum L.) EOs are used in pest management applications, but the most-discussed constraint regards restraining the usage of these natural insecticides in common agricultural practices is related to the volatility and limited persistence of EOs under field conditions. Due to high volatility, the efficacy of these substances falls short after EO application and requires frequent reapplication. There is a great interest in developing formulations that improve the handling of EOs, prevent the photodegradation of their active ingredients, and control the release of volatiles through micro/nanospheres or capsules in solid or liquid form. The polymer-based EO nanoformulations provide the stability and optimal effectiveness of EOs with an anti-insecticidal effect. One of the main advantages of solid formulations is that they can have a longer shelf life and be applied in solid form or even mixed with water and sprayed. We investigated the formation and characterization of inclusion complexes (ICs) of beta-cyclodextrin (β-CD) with two selected EOs, using the co-precipitation method. The main constituents of EOs determined by GC-MS analyses were trans-anethole (37.77%) and α-pinene (23.51%) in fennel EO, and linalool (32.6%) and methyl chavicol (23.2%) in basil EO. The interaction between β-CD and EO molecules was assessed through Fourier-transform infrared spectroscopy (FT-IR) and it was used to characterize the ICs by evaluating the changes recorded in the ICs compared to the free β-CD and individual EO. FT-IR spectra of inclusion complexes displayed peak shifts and variations of intensity when it compared to FT-IR spectra of EOs and free β-CD. β-cyclodextrin resulted as an effective host in encapsulating selected EOs. The potato plants sprayed with ICs were examined by scanning electron microscopy (SEM) and showed ICs with lamellate or rhomboid morphology. Bioassay with Colorado potato beetle fed with potato plants covered with ICs showed that complexation with β-CD reduced insects’ growth (body mass of IV instar larvae where 119.84±1.48 mg and 120.79±7.42 mg for IC with fennel and basil EO respectively in comparison to body mass of control larvae 138.97±2.01mg) and affected digestive proteolytic activity.